Why Fast? Part Five – Exercise

In previous installments, I’ve discussed the powerful effect of fasting on weight loss, particularly with respect to adipose tissue. I’ve explained how intermittent bouts of going without food have been shown to increase cancer survival and resistance and improve patient and tumor response to chemotherapy, and I went over the considerable evidence suggesting that fasting can provide the life extending benefits of caloric restriction without the pain of restricting your calories day in, day out. And last week, I highlighted how fasting may have protective and therapeutic benefits to the brain.

As such you might be thinking that I only recommend fasting to the sedentary, the aged, and the infirm. Surely I wouldn’t go so far as to recommend to the active, the athletic, and the jacked that they engage in vigorous physical activity without having eaten a solid square meal beforehand – right? I mean, no good can come of a fasted training session, as the gym bros with the sweet ‘ceps are so quick to intone.

So, Sisson, what’s the deal? Can we exercise in the fasted state and live to tell the tale?

Yes. And there may even be benefits to doing it. There’s actually not a huge amount of literature on the subject out there, with the bulk of it studying Muslim subjects during Ramadan and getting mixed, sometimes negative results. I’m wary of using the negative results of the Ramadan training studies to color our opinion of fasted training for the population at large for three major reasons: first, Ramadan restricts daytime food and water intake during the fast. If you’re sedentary, you can probably get by without guzzling water, but if you’re an athlete, or even just someone who dabbles in a bit of lifting, some walking, and maybe a few sprints, your performance and results will suffer without adequate hydration. And I’d say a complete and utter absence of water during daylight qualifies as “inadequate hydration,” wouldn’t you?

Second, since eating and drinking are limited to pre-dawn and post-sunset hours, Ramadan often means sleep deprivation. Studies show that sleep onset occurs later than normal, sleep duration is lessened during the month (PDF), daytime sleepiness increases, and general performance of daytime tasks decreases. We’re already aware of the importance of sleep for general health, but inadequate sleep can also translate to poor athletic performance.

Third, the subjects in these studies most likely aren’t on a healthy Primal eating plan. Heck, they’re probably not on a conventionally healthy whole foods diet. While it would be nice to believe that these Ramadan fasters were feasting on fresh lamb, high quality extra virgin olive oil, extra-thick pastured labneh, grass-fed breadless shawarma, and pomegranate salads, they were likely eating the same junk that everyone in the industrialized world eats. And as such, they were probably poorly equipped to shift smoothly and easily to the fat based metabolism required by fasting. Sure, they switched over to burning their own body fat out of necessity and a sheer lack of calories, but it wasn’t the easy, seamless transition that Primal eaters typically enjoy at the drop of a hat. For the carb-addicted, fasting is mentally, physically, and spiritually taxing. For the fat-adapted, fasting often just happens. As we often say around here, we eat WHEN – When Hunger Ensues Naturally. For folks with easy access to the fat-burning switch, skipping a meal (or three) doesn’t ruin the day and preclude exercise.

Right off the bat, then, I’ll say this: don’t even consider fasting and training if you’re not going to hydrate, sleep, and become fat-adapted.

Now that we have those caveats out of the way, let’s look at some of the purported benefits of exercising in a fasted state, as shown in the literature:

Improved Insulin Sensitivity

Intermittent fasting improves insulin sensitivity, as I mentioned before in the fasting and weight loss post. A recent study found that this effect is heightened when combined with exercise (in this case four days of endurance training each week). By the end of the study, subjects who fasted had lower body weights (the only group not to gain weight), better body-wide glucose tolerance, and enhanced insulin sensitivity. Furthermore, only fasted training significantly improved muscular adaptations to training.

Improved Recovery from Endurance Exercise

Three weeks of overnight-fasted endurance cycling (with caloric restriction to boot) improved post-workout recovery, maintained lean mass, lowered fat mass, and maintained performance. There was unfortunately no control group, but this study does show that fasting doesn’t hurt (and it may help).

Another study suggested that fasted endurance training may quickly re-activate the muscle protein translation that was negated in athletes who had eaten carbohydrates before training.

Improved Recovery from Weight Training

A 2009 study found that subjects who lifted weights in a fasted state enjoyed a greater “intramyocellular anabolic response” to the post-workout meal. Levels of p70s6 kinase – a muscle protein synthesis signaling mechanism that acts like an “indicator” of muscle growth – one hour after a fasted workout doubled levels compared to one hour after a fed workout (in the same group). In other words, fasting boosted (physiological indicators of) post-workout muscle growth.

For a further look, check out Martin Berkhan’s take on the study. Also note his recommendation that 10 grams of BCAA (branch chain amino acids) taken before the workout should boost the enhancement without taking you “out of the fast.”

Improved Glycogen Repletion and Retention

What happens when you train in a low-glycogen state? If you’re used to running on full glycogen stores, your performance might take a hit when you have to shift toward a more oxidative, fat-based energy pathway. That’s understandable. Another thing that could happen is you learn to make do with less glycogen by, well, making do with less glycogen. This is elementary stuff, folks. Just like your muscles adapt to imposed stressors by getting stronger, your body adapts to low glycogen training by learning how to train under low-glycogen conditions, thus sparing glycogen for when it’s really needed and boosting performance when glycogen is actually available. It’s the classic “train low, race high” idea that I’ve discussed before. It’s the specific adaptation to imposed demand (SAID) principle, only in this case the “imposed demand” is a low-glycogen, low-food environment.

A recent study exemplifies this phenomenon, pitting a group of untrained, carb-fed cyclists against a group of untrained, overnight-fasted cyclists and comparing both groups’ muscle glycogen content and V02 max. Who won? The fasted group improved their V02 max by nearly 10% and their glycogen content by over 54%, while the fed group improved V02 max by just 2.5% and glycogen by a paltry 2.9%. Lesson? Don’t eat 1.5 grams/kg body weight in cereal-based carbs pre-workout, and definitely do not eat a delicious shake of waxy maize during your workout (unless you really really like cereal and corn starch slurries).

What do you notice? Fasting does not instantly imbue its adherents with super powers. It’s not supposed to. Improved performance during a given training session isn’t really the point of fasted training. The point of fasted training, as I see it, is to maintain performance while enjoying the metabolic benefits, like improved recovery, higher glycogen stores, better insulin sensitivity, and improved muscle response to exercise. The point is that fasted training won’t kill you, won’t eat your muscles, and it might even improve adaptation to exercise by forcing you to train in a “less optimal” state, which can boost performance down the line. The Olympian isn’t going to be well-served by doing the main event on an empty stomach, but he just might benefit from occasionally training on one.

Mind and Matter Matter

The success of your training, whether it be lifting heavy things, running, sprinting, rowing, cycling, or climbing, isn’t wholly dependent on your physical state. The amount of glycogen in your muscles and liver, the mobility of your tissues, the structural size of your muscle cells, the distribution of the fiber types within those muscle cells, the V02 max – these all matter and help decide the amount of weight you’re going to put up, the time you’re going to hit, the miles you’ll be able to check off, and the number of pullups you’ll complete, and fasting will obviously have an effect on these and other markers. But just as important is your mindset, your personal approach to fasted training.

Me, I like a good long hike in the morning with maybe just a cup of coffee in me. It gives me exactly the kind of steady energy I want without negatively impacting my performance (which doesn’t really matter on a pleasant hike) or my enjoyment (which does). However, I don’t like playing Ultimate Frisbee on an empty stomach. I can do it, but I feel like it impairs my performance – and when I play Ultimate I play to have fun and win (as PrimalCon attendees are soon to find out). As far as lifting goes, I’ll sometimes do it fasted, but I’m a big fan of fasting after a strength workout. I do so to milk the post-workout growth hormone surge and because I’m just not that hungry immediately afterward. If immediately stuffing one’s face was required for optimal gains after a workout, you’d think we’d all be ravenous after lifting heavy things, but we’re not. I can do sprinting on an empty stomach, but I hit the wall quicker (probably due to the depleted glycogen).

Don’t let the results of a study (or my words) dissuade you from doing something that seems to help you. If fasted resistance training has you hitting PRs (or at least feeling like you could if you wanted), keep doing it and disregard studies that suggest “THIS IS IMPOSSIBLE. YOUR GLYCOGEN-DEPLETED MUSCLES WILL SURELY DISSOLVE INTO THE ETHER.” If fasted resistance training has you lagging, eat something the next time and disregard studies that suggest “YOUR POST-WORKOUT MUSCLE PROTEIN SYNTHESIS AND INSULIN SENSITIVITY WILL SKYROCKET TO THE HEAVENS ABOVE.” In the long run, it may not matter. People have gotten in great shape eating six meals a day or just one.

Whatever you do, don’t fall prey to paralysis by over-analysis, as did one of the Worker Bees. This guy got way too deep in the fasting literature. He was reading PubMed articles, scouring online weightlifting forums for anecdotes about fasted training and running multiple self experiments with his eating and training. He become so enamored by the idea that working out in a fasted state would elicit superior metabolic and performance effects that he found himself unable to workout if he’d eaten anything at all. And it wasn’t a physical inability; it was a mental hang up. He became frozen, stuck and often unable to reap all these wonderful benefits he spent so much time reading about, all because he felt guilty working out if he’d had so much as a few pieces of beef jerky, a couple eggs, and a banana. Don’t be that guy. He has since seen the light and now realizes that something is better than nothing, that even “non-optimal” training can still be effective. But he wasted a lot of time getting there because he obsessed over studies performed on people who were not him which suggested some (often obscure) benefit to working out in a fasted state.

Do what works for you and if you find that fasted training qualifies, so be it. But don’t think it’s a requisite of Primal living. While I absolutely recommend that people play around with it, and most people find that Primal eating makes it easier, fasted training is not required.

What are your experiences with fasted training? Have you tried it? What benefits, if any, have you noticed? What about particular activities, like sprinting, lifting, or jogging – how do they respond to fasting?

Here’s the entire series for easy reference:

Why Fast? Part One – Weight Loss

Why Fast? Part Two – Cancer

Why Fast? Part Three – Longevity

Why Fast? Part Four – Brain Health

Why Fast? Part Five – Exercise

Why Fast? Part Six – Choosing a Method

Why Fast? Part Seven – Q&A

Dear Mark: Women and Intermittent Fasting

About the Author

Mark Sisson is the founder of Mark’s Daily Apple, godfather to the Primal food and lifestyle movement, and the New York Times bestselling author of The Keto Reset Diet. His latest book is Keto for Life, where he discusses how he combines the keto diet with a Primal lifestyle for optimal health and longevity. Mark is the author of numerous other books as well, including The Primal Blueprint, which was credited with turbocharging the growth of the primal/paleo movement back in 2009. After spending three decades researching and educating folks on why food is the key component to achieving and maintaining optimal wellness, Mark launched Primal Kitchen, a real-food company that creates Primal/paleo, keto, and Whole30-friendly kitchen staples.

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152 thoughts on “Why Fast? Part Five – Exercise”

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  1. I find when I fast and do intensive physical work that I start off slow and then my energy builds. I feel light and good afterwards. I do drink water though.

    1. Brilliant liberty1776! My exact thoughts. I had this experience during my “lunch” break today. I do try to eat within the first hour post-workout. By that point I have typically been fasting for 15-16 hours (since supper the night before.) Great stuff Mark!

    2. I completely agree, Liberty 1776. I often will skip breakfast and go for a quick 20 mile ride on the bike. After about mile 5 my energy is so high that I am peddling like a maniac. Then, after I am done I am completely full of energy, and this often lasts till lunch. This is not to say that I get sluggish near lunchtime, only that the super-duper energy has subsided to only super energy. 😉

      Also, I’ve found that when I do a 24 hour fast every now and then, that my energy levels are good and steady all day long, regardless of activity levels. However, I will admit that if I get too active on those days that my hunger mechanism kicks in (which makes sense).

      It is so awesome being fat-adapted, because you never really deal with ravenous hunger or loss of energy levels like many of those who rely on carbs for all of their energy needs. I seem to go from using dietary fat for energy to using body fat for energy as easily as flipping a switch. I just cannot stress enough how truly awesome that is.

    3. During a fast your body is already up-regulating catecholemines such as epinephrine, norepinephrine, and cortisol. When you train in a completely fasted state, your body pumps out even more more adrenaline, noradrenaline, and cortisol to release fatty acids and glycogen from fat cells and the liver, respectively.

      The effects of fasted training is almost always a light focused feeling.

      You really can’t beat the benefits of fasted training.

      Not only will you see the metabolic benefits, and increases in performance, but you can actually REVERSE AGING.

      I talk about this extensively on my website, The Fountain of Youth and Strength.

      Remember, if you do decide to train with BCAA before a fasted workout you will lose a large part of the benefit of low insulin. The mTOR pathway will be activated, and autophagy will be down-regulated. You will also most likely lose the increase in protein synthesis that completely fasted training provides.

      1. That’s interesting as I’ve finally got into the habit for an all-day fast to work out at 5pm or so. I just bought a container of BCAA’s to try and get some extra boosts to muscle growth and haven’t tried it yet. What is the evidence for/against BCAA’s breaking the fast?

        1. Well there are hardly enough studies to even really decisively conclude that fasted training is superior to fed training. I know there are no studies done, or coming in the near future, that analyze the differences between completely fasted training and training with BCAA, so we just have to use common sense.

          BCAA’s are extremely insulinogenic, and fasting is really defined as having low levels of insulin. So you jack insulin up with BCAA, you activate the mTOR pathway and you lose part of the benefits of autophagy.

          Not only this but the increased protein synthesis that occurs post-fasted workout, occurs exactly because your body is attempting to adapt to be able to handle another strength training session without protein in the bloodstream. When you workout with BCAA you are giving your body much of the protein it needs for protein synthesis while you are working out, so why would your body adapt to synthesize more if you didn’t create the demand for it?

          It is also a fact that GH declines in a high insulin environment, so by jacking up insulin with BCAA you are not going to see as high of a GH response for strength training.

          Martin, over at leangains is a bit obsessed with preventing protein catabolism, but the protein catabolism that occurs during fasted training is catabolism of damaged proteins by autophagy to be recycled, and this is actually beneficial to health.

        2. Ok that’s quite interesting and I didn’t realize that. Are the large GH spikes during fasting utilized when you finally break the fast for better growth response from muscles or does that all evaporate with the insulin reponse?

      2. So Matthew,

        If you were trying to achieve hypertrophy, would you train in a fasted state and not take BCAA’s and not eat for a few hours afterwards to increase GH? Or would you not be in a fasted state and take BCAA’s and then eat after? Or alternate between fasting and not fasting on workouts maybe?

        p.s. I like the way you look at the primal thinking/way of living and combine it with physiological reasoning.

      3. so are you saying that if i have been fasting I shouldn’t drink BCAA’s during my workout?

    4. I agree. As an endurance cyclist, I was conditioned early on to train on an empty stomach; only consuming water during training rides. I’ve found my body adapted over the years. It has become efficient at utilising food – whether training or during recovery. I’ve also found maintaining my ideal body weight a breeze as a result of such conditioning Thanks Mark!

  2. Thanks for the great post, and the link to the PDF, Mark.
    I’m only going on my second week of eating this way and incorporating your fitness advice, and I am already feeling terrific results. In fact, I am Muslim, and one of the first things I thought about, once I started experiencing the lack of hunger when eating this way, was how much simpler Ramadan will be this summer. Yes, it will still be a challenge, due to fatigue and lack of sleep, but that carbohydrate-driven hunger doesn’t have to be a part of the equation. Brilliant.

  3. I’ve had some experience with fasting and exercising and I’m still experimenting and trying to figure it out, but I’ll share my experiences so far and questions.

    First off, let me say that I had done 1 day fasts (from everything but water) prior to going primal (well, trying to be mostly primal…probably usually around 80%…sometimes much closer to 100, sometimes worse), and the difference is astounding. In the past going without anything but water for an entire day seemed like torture, so hungry, no energy, light-headed, etc. Now it’s no problem at all. Sure, I’ll get hungry, but I otherwise feel fine and have a normal energy level.

    Also let me preface this by saying I typically work out first thing in the morning, without having anything to eat since the night before. I don’t consider this exercising in a fasted state, but maybe it technically is? (It’s usually 10-12 hours since dinner the night before.)

    When I’ve done those one day fasts, I feel good working out, both on the day I’m fasting and the next morning (so now two nights and one day of fasting later). I haven’t experimented with it enough to be able to say that it is noticeably beneficial or detrimental to the workout(s) or certain types of workouts, but it’s pretty much like it normally is for me. The biggest thing I’ve noticed is that it is important to stay hydrated….I think I tend to get dehydrated more easily when I’m fasting if I’m not careful.

    Where I’ve experimented only a couple times with more mixed results is with longer fasts (2-5 days). I’ve done that a couple times, and have found that while fasting I’ll still work out but purposefully not go at 100%, but keeping up my normal routine at about a 75-85% intensity level works well and I feel great. Recently I just fasted over the Easter weekend in conjunction with Holy Week observances, so it was part of Thursday through after church Sunday. Felt good during, and then ate normally Sunday (well, maybe a little more sugar than normal). Worked out a couple times during those days and felt great and had energy (although didn’t push myself to 100% intensity in either lifts or metcon type workouts) but Monday morning workout out I felt absolutely terrible — felt weak, no energy, mentally foggy, etc. Not completely sure why, although I could tell I was quite dehydrated, so maybe it was more related to that than anything else.

    I do like working in some fasting to my routine for both health and spiritual reasons, so I’m going to keep experimenting with it, right now with placing emphasis on staying well-hydrated.

    1. After around 12 hours of a light meal (600 calories) insulin will be at fasted levels and you will technically be in a fasted state.

      If you were dehydrated that could have been the reason, but if you were fasting more than a few days, then didn’t do a large enough refeed, or if you didn’t eat enough protein during the refeed, then you probably had very low levels of leptin, and that could also explain your symptoms.

  4. I recently ran an experiment based on this article series of fasting as 20 / 4 sequence, and i found that my mind was useless during the day (bad for maintaining gainful employment) and that in the evenings when i would eat, i’d end up with stomach aches and headaches (atypical for me… very rarely get either). Went at it for 3 weeks before i decided id push back to a 16/8 type fast, i’m testing it now, but i’ve only been at it a few days, so we’ll see what comes of it.

    (eaten paleo since mar 11, 12% bf)

    Anyone have any thoughts?

    I really want to be able to enjoy the benefits of fasting! 😡

    1. Hi Sdiguana,

      I only eat two meals a day on most days, so I’m constantly on a 16/8 schedule, but I’m not anal about it. It’s been the best set up I’ve found so far. I supplement my mornings with coffee and never really go hungry. I recently started incorporating 2 – 24 hour fasts into the week too (Monday and Thursday) because… well.. because of all these Fasting articles.

      So I eat Sunday night, and then I fast on Monday, work out in the evening, and then feast.

      I added the Mon & Thurs fast just a couple of weeks ago and I’m really enjoying it. I’m realizing now that I was eating way too much good food – more than I was really using.

      I don’t know if this works for everyone, but it’s helped me out.

      1. Hi Bruno,

        I am doing the same exact schedule as you and appears to be working perfectly. Dropping fat like crazy and my strength is going off the charts. I need to buy more weights and new clothes! Thank goodness my food costs are down!

    2. Hunger and thirst are highly evolved feedback mechanisms, listen to them. Hungry? Then eat. Thirsty? Then drink. I do not pick my days or time period to fast, my body does. I just listen.

      1. That’s great that you understand your body’s signals. Most of us though, until we’ve become fully fat-adapted and restore the default settings of insulin sensitivity and all that, and have fasted enough to remember what real hunger feels like, will confuse our body’s messages with cultural factors like time of day, boredom, and certain activities and days.

        1. I echo the cultural factors, especially boredom. I use to do many detrimental things to my health when bored, like getting bombed on and then eating a whole pizza; which I ain’t gonna lie, it was pretty awesome! But now that I know the word for this behaviour I just say it to myself, “akrasia”. It has not failed me yet.

      2. I agree with this. I don’t live by specific times to eat. I’m a pre-dawn runner and weightlifter, and I rarely eat before my runs or workouts. I’m just not hungry at 5:00 am. Unless I’m doing weekend long runs, I am fine running and working out on an empty stomach. I prefer it actually.

      3. You can train your body’s appetite, to an extent. I took a leap of faith after reading leangains.com and did just that. Now, I “fast” 15-16 hrs./day, and my body gets hungry only at lunch and dinner times.

        1. Same experience here. I used to think I was seriously hungry every four hours–but it was only my head, and the fact that I obsessed over what the “best diet was” and based on the literature I had read, small frequent meals was the way to go. Then I started reading about fasting and gave it a shot–it was hard to eat so much in one sitting at first, but I quickly got used to it. I have more clarity at work; have better workouts (I used to sometimes end up with an upset stomach during training if I ate too soon before); and it’s simply convenient. It doesn’t work for everyone, though. If fasting causes you the same problems frequent meals caused me, listen to your body and base your diet on its feedback. I think the “best” diet is very individual to each person.

      4. Liberty, that is actually how my very first fast started. I was at work and our first break came up. Usually I will have a small snack or a salad during break, but I simply didn’t feel hungry. So, I decided to wait until lunch, but when it came around I still wasn’t hungry. I didn’t eat until around noon the next day when my hunger mechanism said, “ok, time to eat”. That entire time I felt awesome.

        I try to get in a 24 hour fast at least twice a month, but I don’t schedule it, I just wait for it to arrive. Also, I often skip breakfasts because I just don’t feel hungry. A little cup of tea and I am good to go.

        The strange thing about all of this is that I have a highly labor-intensive job (demolition), so you’d expect me to get hungry all of the time. 2-3 good meals a day and I’m good.

    3. You don’t need to fast that long to get the benefits of fasting. And there is evidence that the hormonal state that produces the benefits of fasting comes from abstaining from CARBS (and excess protein), not abstaining from food entirely.

      So effectively that means you can eat little bits of energy-sustaining fat (like coconut oil — try adding 1 Tbsp to coffee — produces ketones very rapidly) and still be in a fasted state.


        1. Tried it!

          I’m not sure if it had much of an effect on my ketones… and it was kind of hard to choke down the feeling of straight oil, since the oil sits on top of the coffee.

          I might try this again in the future, but I think I might just stick with plain black coffee on my fast days.

    4. If you are training too much or too hard, as I find most people are, then you will not find fasting enjoyable, and you will not be coherent or productive during a fast.

      You shouldn’t have more than 2-3 hard training days every week. Hard training shouldn’t extend past an hour. Keep exercise light, such as walking, on other days.

      Some people have an issue getting in enough whole food in a 4 hour eating window, especially with the satiating effects of protein. You may have not been eating enough, which would have led to low levels of leptin. 16/8 or 18/6 will probably work better for you.

      Stomach aches and headaches after eating sound like an allergic reaction or a food intolerance. Check out Mark’s articles on lectins and see if you are consistently eating foods on that list. Eating the same foods day after day will lead to food intolerances.

      1. I agree, I workout (LHT),fasted 3 days/wk, and in between do some LISS, usually walking, I love it. I typically workout between hours 16-18and of my fast, my fasts are usually 16-20 hours with no problem. However,if I throw in a HIIT workout too often or my LISS becomes more intense than usual I can always feel it in my next fast right away.

    5. I think that the series of articles was about IF, intermitent fasting. What you are doing is consistent feast /famin scenario. There are some great books on this type of ‘eating window’ lifestyle. eg. Ori Hofmekler has one, which might help “The warrior diet”. He dosent advocate a total fast in that non eating window either !

      Fasting for me isnt so much about not going without food all the time, I fast 24 to 36 hours once a week ! Ocasionaly missing a meal and I dont eat past 6pm, but thats just me. Start off with one day a week, chose one that dosent clash with your work, eat in the evening and then fast till the next evening and eat then, thats 24 hours, once you can handle that OK , do 36h or so , just by going to bed and thereby extending the fast till next morning. You can excercise on that day to gain some of the benefits outlined in this article without compromising your work.
      Every now and then, especialy when I feel not quite well I fast longer 2 -3 days which is easy after the first day anyway.

      Intermitently fasting is to supprise your body with no food, just like a failed hunt. The physiological adaptations outlined here make sence, next hunt your body wants you to be stronger to ensure the hunts success.

  5. I fast twice a week for 24 hours. I like to have a big workout right before my long awaited meal. I find that I work harder when I have a hot dish waiting for me, and it feels super rewarding to finally eat.

    I do feel like “that guy” sometimes, though, because I don’t like doing anything active on a full stomach – but a few pieces of jerky or a couple eggs wouldn’t be enough to dissuade me.

    I played Ultimate Frisbee just last night for the first time this season. I think this is the first time I’ve played while fasted. I had a tremendous amount of energy and stamina. I’m pretty terrible at UF… but I.did.not.stop.moving.

    1. I’m with you on that. It’s not so much that I find I can’t perform when I’m fed, as much I find that the fed state is a time for relaxing.

      I find the energy to train hard and be active when I’m fasting, and I know I enjoy it more.

  6. And by the way, I’m very glad you’re writing about this! You’re right — there is not much out there in the way of resources about this! I’ve tried to find something helpful regarding keeping a consistent routine with my training (i.e. able to go as hard as I want when I want to (although for me that certainly doesn’t mean 100% every day anyway)) while able to incorporate fasting and there’s not much. Thanks!

    1. Another valuable fasting resource, which I learned through MDA, is leangains. com

      1. Ditto. Leangains is a great resource of information and ideas on the topic.

        He offers a variety of ways to approach it… because we lead a variety of different lifestyles.

        One of Mark’s last lines really resonated with me: “Do what works for you and if you find that fasted training qualifies, so be it.”

      2. Christina, if you enjoy the Lean Gains plan, here is an easy calculator to get you started with calorie/nutrient intake guidelines. This saved me a lot of time, trouble, and stress. I don’t count calories on a daily basis, but think it’s good to begin with a basic plan. https://www.1percentedge.com/ifcalc/

    2. I offer all my online clients a fasted workout protocol and meal guidelines. My entire protocol is centered around fasting and helping my clients work their way into fasting and fasted training.

      Right now I am offering two weeks of my online services for less than 25 dollars.

      If this doesn’t interest you, I also write extensively on the benefits of fasting and weight training on my website.

        1. Personally, I appreciate all of the FREE knowledge Matt has shared with us. He obviously has a very good understanding of the subject and is nice enough to share it with the rest of us. I don’t mind the occasional plug for his business, he doesn’t do it in every post.

  7. Really enjoy this series. I have been “primal” for quite some time (over a year) and have been doing 1-2 24 hour fasts a week ala Brad Pilon’s Eat Stop Eat for over a year now, and find that both blend perfectly well together and are easy for me. Some of my most intense workouts (measured against previous times/weights/reps, etc) have occured 23 hours into a fast. It’s all a matter of what works for the individual.

  8. I have been exercising since I was 18 in a fasted state (swimming, hiking, weight lifting, stadium climbing etc). I usually exercise first thing in the morning. I am 44 now. I always perform better on an empty stomach. I do drink at least a gallon of water a day and more when I’m exercising. Since I cut out all grains (2 years now), I have noticed my performance and recovery have improved.

  9. I do water “aerobics” mid-morning once a week. (I put aerobics in “” because it involves full sprints and lots of resistance.) Often I will supplement with some overhead weights in the gym. I nearly always do the workout with only water or (decaf) coffee and have plenty of energy.

  10. “A 2009 study found that subjects who lifted weights in a fasted state enjoyed a greater “intramyocellular anabolic response” to the post-workout meal. Levels of p70s6 kinase – a muscle protein synthesis signaling mechanism that acts like an “indicator” of muscle growth – one hour after a fasted workout doubled levels compared to one hour after a fed workout (in the same group). In other words, fasting boosted (physiological indicators of) post-workout muscle growth.”

    This makes total sense. You don’t eat the animal then hunt it… you hunt it then eat it!

    1. As much as our ancestors were HUNTER-gatherers, they were also hunter-GATHERERS. It’s not like animal food was all that was available, such that once they finished off the last animal, they had no food at all until they bagged the next one.

      It is at least as plausible that they were eating the gathered plant food – i.e., carbohydrate – pre- and maybe also during-the hunt; then, high-pro, high-fat post workout.

      “Fasting as much as possible” or “never fasting” are not the only two options.

    2. Unless, of course, you have some jerky left from yesterday’s hunt. Or last week’s, even. Or you fished, or you caught something in a trap, or your family caught something earlier, or you went foraging for nuts, berries, roots, shoots, and insects, and then went hunting after breakfast, while you had a full stomach and high energy.

      Helps to remember that not only were ancient humans resourceful, they were also social–or else they weren’t apt to be long-lived.

    3. I agree with you on this. Hunting probably would have taken place when food wasn’t just lying around to be eaten, otherwise people would not have been hunting in the first place. Makes sense, right?

      However, these adaptions also make intuitive sense from and adaptive perspective. Your body will synthesize more protein and store more glycogen in response to fasted training, because it is adapting to the environment, or the state your body is when training usually takes place. Your body is trying to adapt to the metabolic demands you are placing on it by storing more glycogen and protein in muscles, so that it can cope the next time you train fasted.

  11. Thanks for the great post, Mark.

    As of late, I lift heavy and trail hike fasted–simply because it makes no short-term difference in my training or enjoyment of the activity and it’s more work to prepare and consume food before hand. I also wait until I’m hungry to eat after an exercise session, which is sometimes immediately and sometimes 1-2 hours post workout. I will have a peice of fruit 1/2 hour before sprints though, as I gas-out quickly if I do it fasted.

    I have noticed, over the course of the past few months that my strength has improved dramatically (i.e. from maxing out at 20 pull ups, where I have been stuck for years, to 25 last week), which surprises me, as I wasn’t really training any differently. I do think it might have something to do with the fasting, although I can’t eliminate all the other possible confounding variables.

    At any rate, IF and fasted training is working for me and I don’t plan on changing that anytime soon.

    1. My wife noticed how much more focused and stronger I have become since working out in a fasted state. I hear ya!

  12. I am training for a half marathon (and not enjoying it) and I have found that I have the most success with distance in the morning. I do have some coffee and maybe a smoothie an hour before going out to take the edge off and give me a little fuel, but much more than that and I feel sluggish and heavy. When I run later in the afternoon after work I feel like I am always struggling the whole time. I feel slow, heavy, and I tend to get side aches. So this all makes sense to me.

    1. Sorry for pointing out the obvious, but if you are not enjoying your training for your half marathon, then maybe you should stop and do something else. I don’t mean this to be snarky or mean. I can’t imagine enjoying running that much.

    2. I have to second Philmont Scotts sentiment–life is too short to put so much time and energy into an optional activity you don’t enjoy.

  13. I can run and walk fasted, but if I do heavier exercise, such as my hour long TRX class or go to a BodyPump session, I need to have eaten earlier in the day or I run out of steam.

    1. Those kind of training sessions deplete a severe amount of glycogen. Brief HIT strength training sessions lasting 30 minutes to and hour will not have this effect. Glycogen depletion will be moderate.

  14. While reading this I realized that just yesterday morning I’d worked out in a fasted state. I was so motivated to work up a sweat and felt so energized that I hadn’t even considered eating something before. After my 30 minute session I didn’t eat for another few hours, just because I was busy with house work and I wasn’t hungry yet. I don’t always work out fasted but when I do, it’s not usually planned. I just do what I feel like and give my body what it needs. Definitely would NEVER have been able to go that long without food, let alone WORKOUT fasted, without being secure in my Primal habits. I’m sure most people who follow CW must think fasting in general is just insane and that it has to take a ton of agony and willpower. I love the freedom that comes with being a fat burner! It’s made life so much easier.

  15. I have been mostly primal for 2 years now. I try and hold off eating each day until I get truly hungry. Sometime that is 9am, other times it’s after one of my 12 noon lifting workout and can be as late as 2:30. I have a loss of appetite after lifting for an hour or more. I have sometimes tried to hold off eating until after my noon lifting and I have found that on days when I had to really work at not eating due to hunger, the workouts suffered. On days when the fast came easily, the workouts were great and better than normal. I think my hunger signals need to be listened to, for me at least. I have never gone more than a 19 hour fast.

  16. I walk 3 miles every morning fasted (usually about 10-11 hrs at that time) and find I am more energized afterwards. It also seems to make any “hunger pangs” disappear.

  17. I have been participating in 16-20 hour fasts since the beginning of January 2012. I have also been following the Body By Science Big 5 workout since Christmas 2011. I have been Primal for more than two years. Yet my weight, lean body mass, body fat and measurements have not changed!

    Granted, I do have leaky gut and hashimoto’s; these have been leveled out through diet and lifestyle. I absolutely love IF and Primal as a lifestyle and will continue it indefinitely. Thanks Mark, for showing us the way! I just cannot figure out which piece of the puzzle I am missing.

    I started at 275 pounds and have been lingering around 190 lbs and 21% BF. My caloric intake is between 1600 – 2200 daily – while fasting 16 – 20 hours 7 days a week. Carbs are under 100 grams everyday. I work out in a fasted state and I also implement an occasional bout of sprints, as well as daily walks with my wife.

    Mark stresses quality of exercise, not quantity; as he does regarding our diet. What am I missing??

    1. How about trying to get into and stay in ketosis? If your 100 grams of carbs come all at once, you will be leaving ketosis. Give yourself 3 weeks of carbs as low as possible (leafy greens only), no tubers, no nuts, no seeds. See what happens.

  18. I exercise in a fasted state 5 days a week. I exercise first thing in the morning before I go to work, so I don’t really have time to eat something, let it digest some, and then exercise. I go into work early in the morning so I can leave earlier in the afternoon… so I have time to play at night 🙂

    If I am going to exercise with a meal in me, I need to have at least 30-60 minutes post-meal before I feel like I can exert myself without feeling gross.

    I have been exercising in a fasted state for a few years now and I have made steady gains in strength and endurance. I will even fast after the workout until lunch on some days without any negative effects.

    To Mark’s point – if it works, run with it. If it doesn’t, run with that.

  19. I have been eating primal for over two years and last year did most of my long distance cycle training in a fasted state. Three and four hour rides at low intensity felt wonderful! I participated in 5 “events” and usually ate a banana or homemade trail mix during the ride. Bananas are perfect high octane! I had my Best season ever.

  20. I have exercised twice now at the end of a 24 hour fast. First was a week or so ago, I was just curious how I would do cycling on hour 23. Did a 12 mile ride, had a great experience and felt no loss of energy or Bonk. Still had the tingle of hunger, but nothing that wasn’t easily manageable. This week I went for a 3 mile trail run after fasting. It was a little more difficult, but still overall a good experience. So much for the need to carbo load prior to working out. I also went fishing out of my kayak for a few hours Saturday morning without eating in a local river. Awesome experience. Being hungry and in the woods looking for food early in the morning was an amazing experience. Felt more in tune with my surroundings.

  21. Here’s the absolute best reason to exercise and work out in a fasted state, and specifically a carbohydrate and glucose restricted or fasted state: CARDIAC FUNCTION. 

    “Methodist DeBakey Heart & Vascular Center scientists learned that starved heart cells maintain normal calcium cycling and basic mitochondrial function far longer than non-starved cells during periods of extreme stress.

    The findings… add to a growing body of scientific evidence that suggests the consumption of less energy — while maintaining balanced nutrition — can benefit tissues by enhancing cell performance and reducing DNA damage associated with the aging process.

    “We are connecting several loose facts about calorie restriction and heart function, in particular, arrhythmias,” said cardiac electrophysiologist Miguel Valderrábano, M.D., the study’s principal investigator. “We have shown why nutrient restriction protects the cells from ischemia and reperfusion. Normal function means less risk of arrhythmias, during which heart cells stop communicating properly with each other, and which can cause further damage, even sudden cardiac death.” ”  https://goo.gl/odq7F

    As I have previously mentioned here & elsewhere I have been investigating the link between high carb diets, carb loading and sudden unexplained cardiac death (SUDS) commonly seen in marathoners such as the recent death of 56 year old vegetarian mountain runner and “superbly conditioned” Micah True who was found dead on a trail after having gone missing for 4 days. 

    Although the researchers of this study repeatedly describe and attribute the beneficial effects to “nutrient” restriction, it’s interesting to note that the nutrient they restricted was a “blood-serum medium containing glucose” but NOT proteins or fats.  It’s also interesting that they seem oblivious to the existence of the other macronutrients, at least for the purposes of this study, and that the study actually points the accusatory finger carbohydrates but without specifically mentioning, highlighting or drawing attention to that fact. 

    This study correlates with the other studies I’ve mentioned & linked to in the past showing a loss of activity in up to 50 percent of heart cells during extreme output athletic marathon events, and the use -in this study- of glucose as the specific nutrient provides further proof that carbs & carb loading causes a cascade of effects that negatively impair cardiac electrical signaling & function, such as glycation of critical signaling & cellular membrane ion channel proteins, electrolyte imbalances, etc. 

    Instead of training for & signing up in the next marathon I think I’ll just keep drinking my butter coffee & keep my body in a ketogenic fat burning mode by restricting carbs. As it turns out and is becoming clearer, carbs & wheat are not really murder, it’s more like suicide. 

  22. Thanks for the great post!
    It might be interesting to note as well that during Ramadan, people tend to gorge themselves on “sweets”. I mean seriously ridiculous amounts of sweets with all that sugar syrup. They seem to think they won’t last the day without loading up on carbs! I think the wisdom of spending a month eating less gets lost, and a lot of people end up stuffing themselves and eating more in those few hours of dark than in a normal day.

    Last year’s Ramadan was so much easier when I had given up all sugar, and tried to go 70-30 primal. Thirst was soo much less of a problem even though I was in Arizona, and did a good deal of exercise right before dinner, so I could eat and drink right after.
    Around 4 months ago I got really commited to primal and I’ve been going more like 90-10, I hope this summer it will be even better.

    1. Hi Mark, Thanks for this post. I am a Muslim who went Paleo in July last year, 2 weeks before the start of Ramadan. I had read about it, and then experimented on myself. Where I live in London, the fast was from about 4am to 8/830pm in the evening. I went completely cold turkey on refined carbs: no grains, no wheat, no potatoes, or corn, and very little fruit. If I had fruit, it was only a little and late at night so I wouldn’t experience the hunger cravings that came followed the sugar rush. I didn’t have any sugar either.
      As part of my daily commute, I was cycling 20-30 miles a day too.

      I have never known Ramadan to be so easy. Not only did I get leaner, I lost fat, built muscle, and because I was eating lots more fats, I did not need to eat so much, and found I could drink more water before sunrise. Towards the end of the month, I started loading up on even more fats, usually in the form of double cream, and/or fatty meats and found that I did not need to get up for the pre-dawn meal, so was able to sleep through and get a full night’s sleep. My son’s birthday fell during Ramadan. This involved a picnic by a river. That day I fasted and swam a kilometre in the river, and experienced none of the crashes and crabbiness that have characterised previous Ramadans. I had no cravings, had loads of energy and was more alert than I have ever been during Ramadan.
      Paleo-fasting meant that I was able to get more sleep, drink more water, and had more energy than when I have fasted incorporating refined carbohydrates.

      I find myself looking forward to Ramadan this year as an opportunity to get even fitter than I am now.


  23. I have been doing a 16/8 daily IF for 1 1 /2 years and training in a fasted state. I have played with all different pre/post workout fuel options and prefer to train fasted and then eat a large meal afterwards.

  24. I’m confused.
    One should eat protein and carbs 30-60m post workout to build the muscles
    Am I wrong?

    1. As I have heard it, no. That’s commonly heard, but leaving eating 30 mins plus means you get the most out of a post-exercise growth hormone surge (GH and Insulin compete for receptors, so carbs are a no for GH)..and increased post-exercise insulin sensitivity (which will drive more protein/nutrients into muscles for muscle synthesis) lasts a few hours after the exercise. So, it’s best left a bit.

  25. Due to these articles, I have been trying just fasting 8-9 hours a day. Picking a time when it is inconvenient to eat, or easy to skip eating. I felt really great. I drank mint tea – peppermint helps with hunger – and I noticed a big difference. I still had three meals, I am just giving my body a break from digesting.

    I ended one of them in a cross fit workout, which as someone else mentioned, started slow, but felt better as I progressed. My mind is much clearer and I felt some weight loss. I am really thankful to Mark for writing these articles.

  26. I am a HUGE proponent of fasted training. After a glutenous honeymoon in September, I decided to give fasted training a try. Now I typically begin a fast after dinner, continue it through the morning, workout around noon, and then break the fast with a nice refeed for lunch. I do follow Martin Berkhan’s advice and have 10g of BCAA before a workout, but other than coffee (black) and water, that’s it. I got over the mental hurdle (CW telling me that I needed to eat for energy) pretty quickly and I can honestly say that I haven’t noticed even the slightest drop off in performance. In fact, I’ve gone up in all my lifts, but I think I can attribute that to starting to do a 5×5 routine, which is a lot of intense lifts (deadlifts, squats, bench press, pull ups) done for 5 sets of 5 reps each.

    I basically never workout within a few hours of eating anymore. It’s not that I feel like I can’t; it’s just that I don’t want to. Before fasted training, it was such a hassle to plan workouts. If I was running errands on the weekend, I would rush to get home so I could eat something, then wait an hour and a half or so, THEN go workout. SO much easier now.

    This is just one of many primal concepts that make my daily life so much better. And now that I am totally fat adapted, it’s actually pretty easy to train in a fasted state.

      1. Thanks! I’d love to say that I’m a beast for being able to do that, but really I saw no change in energy when I went to fasted workouts (I technically started 5×5 a few months before starting to train in a fasted state).

        BTW, although my honeymoon was no doubt filled with gluten, I really meant “gluttonous.” hehe.

    1. I find everyone’s comments interesting. Although there may not be a lot of tests regarding fasting and training I highly recommend everyone to check out Brad Pilon’s Eat Stop Eat. In my opinion it is the best technical and informational guide there is and definitely has good information regarding training.

    2. To me, that’s the best part of fasting–simply not worrying so darn much about food and eating! I used to plan out my six “balanced” meals a day (protien, fat, carbs, fiber, etc.) I had lists and lists with the counts for everything! I carried food with me everywhere! I still carry nuts with me, but now I just eat when I’m hungry and eat simple things like nuts, meat, occassionally some veggies and fruit, and cheese. Easy Peasy Lemon Squeezy!

  27. Wow…fasting every other day sounds a bit intimidating, but maybe introducing some fasting periods a few times a month would be a good place to start. I’m definitely curious since I’ve heard all of the studies about calorie restriction and increased lifespan.

  28. I have been committed to the primal diet since January of this year and recently (last month or so) began experimenting with IF. Mon, Tues, Thurs & Fri I’m on a 16/8 schedule and I fast all day Wednesday which usually amounts to about a 30-36 hour fast. On the weekends, I eat when I’m hungry…
    I dance hula on Wednesday nights for about 2 hours duration (about 20 hours into the fast) and have found that my endurance, mental clarity and ability to focus on the dance have all increased since I started fasting. It’s not a consistent, intensive workout but there are certain times I would equate it to sprints and it is certainly a strength workout.
    I really enjoy IF and definitely plan to integrate it into my long-term routine.
    Thanks for the article!

  29. I am a Bikram yoga fan, and over the past 18mos I’ve found that the 90 minute classes are easier for me to enjoy in the morning, when I haven’t eaten for 12-16 hours. I do sometimes eat 1/2 a banana an hour or two before class so I don’t bonk before class is over, and after class I’ll often drink a coconut water to help with recovery. Usually I end up going 20 hours without a meal because I’m not hungry after class. Since going Primal last month I’ve reduced my classes from 4-5x/wk to 2-3x/wk so I can incorporate more hiking (spring time helps too) and working my way to full pull-ups.

    1. @yoolieboolie: Thanks for sharing the insight with Bikram yoga in the mix! I’m also curious if others have successful strategies for incorporating fasting with primal and Bikram Yoga. I’m going to try it this weekend, fasting from dinner Friday until after a noon Saturday class.

  30. Interesting stuff, thanks Mark.

    I always fl much better doing my early walk or swim on an empty stomach, or just a cup of beef extract at least an hour before. Anything more in the tum makes me fel nauseous. I’m so glad to see it is helping my muscles too!

  31. Remember, there is nothing natural but only damaging if one chooses to use “chemotherapy” as a cancer “therapy”- building of the immune system is number one priority- something chemotherapy does the exact opposite of. Natural foods and methods are much more productive. :~}

  32. I’am on a paleo diet for just over 6 months now, but I can’t do a fast of any kind and always hungry. I see all this talk about listen to your body and how you should feel sated eating primal, but I eat 4-5 times a day total around 3.500kcal (60% fat, 30prot, 10carbs). Does anyone have similar issues?
    (sorry about poor english, I’m from Brasil)

    1. Hi:
      I have a friend at work with the same issue. Check again your carbohidrate grams per day, maybe they are more than you think. Some people have more difficulties than others. It will not hurt if you check your thyroid with your doctor. Regards and good luck!

  33. I’m a hardcore skier, and on powder days I’ll head out the door with nothing but coffee in my belly then charge hard for hours before I lose energy. Then I usually eat post-ski. But I can ski many thousands of vertical feet in a fasted state just fine.

  34. I have written extensively on the benefits on fasting and strength straining on my website. I explain how growth hormone, autophagy, and telomerase all benefit from fasted training and how these things can actually reverse aging.

    I always try to train completely fasted. No BCAA or whey protein, beforehand. I just deadlifted 315 lbs for five reps three days ago completely fasted.

    1. Matthew,
      What`s you opinion if I break my fast after 14 hour with 15g wheyhydro at 10am and again 15g wheyhydro at 1pm, weight training at 3pm.
      Do you think it`s better to go totally fasted till training ( 19hour fasting )?
      Hope you answer or somebody else.

  35. I’m relatively new to the primal life — went low carb about 2 months ago and finally primal about a month ago — and recently discovered intermittent fasting too. Before ditching grains, sugar and starch, I never would have thought any kind of fasting was for me, but now that I am fat-adapted I have found that I thrive on a noon to 6pm eating schedule, ESPECIALLY when I have done some kind of moderate cardio exercise (a long walk or a 40-minute workout on the elliptical) with nothing but a coffee beforehand. For me, working out in this condition means I am literally buzzing with energy for the rest of the day. I haven’t tried any kind of heavy lifting or strength training while fasted, so I can’t say for sure on that matter, but fasting + moderate cardio for me = WIN.

  36. I fast once a week (almost 24 hours), usually on Tuesdays. The fast day does not interfere with my workouts. In the beginning of my fasts like one year ago at the end of the day I felt hungry like hell and as soon as I got home I had to eat something. Not anymore: after the (usually) 22 hours I am ok, I could go on easily for 20 hours more.

  37. I’ve been eating Paleo for about 6 weeks and have lost an amazing 23lbs. Started at 213lbs. and now weigh 190. I just started adding IF using the 16/8 ratio 3 or 4 days a week. I recently checked out leangains.com and it seems he is quite fat conscious which surprises me and seems to embrace carbohydrates as well. Not sure what to think as his clients get amazing results. I’ll probably stay Paleo focused while including IF as I’m feeling great and see no need to change. Anyone else wondering about this feel free to comment, I’d be interested in hearing your views.

    1. John, Martin is catering to a crowd of people who want to get buff. Mark seems more focused on general health and fat loss. I think if someone has a lot of weight and isn’t too concerned about building muscle, primal is the way to go. If someone is skinny and trying to gain muscle, Lean Gains would be a better fit. I used to be 220 lbs and mostly followed a primal diet. I cut down to 170 and decided to switch focus to building muscle, so now I’m following Martin’s suggestions on spiking carb intake. Both approaches work, but are made with different goals in mind.

  38. I recently (2 months) started following the Martin Berkham Leangains method to IF, and lift at the end of the fast and eat immediately afterwards. I actually prefer this as I like working out on an empty stomach. I look back to all my training over the years when i thought you HAD to eat beforehand, and there were some times I’d go to the gym on an empty stomach because my schedule didn’t allow a meal beforehand. I went in expecting to have a crappy lifting session, and would be surprised to have a really good one. Thought it was just random, but now I realize there is legitimate science to back it up.

    In terms of Grok, this makes sense. I seriously doubt he ate a square meal before he went hunting. The whole reason he went hunting was because he didn’t have any food!

    1. I used to be the same way. I’m happy you actually had productive training sessions–if it happened to me, I was so obsessed with frequent intake that I created a self-fulfilling prophecy: I expected a shitty workout, so I had a shitty workout. Now that I understand why fasting works, I don’t have the same problem–they’re actually more productive than before. It makes more sense, too, from Grok’s standpoint.

  39. I have always trained fasted by training at 5 a.m. But I would rush home and have that post workout balanced meal.

    The past 8 weeks I actually started leangains protocol and finish dinner by 7:30 p.m. CrossFit at 5:30 a.m. and eat first meal @ 11:30 a.m. I am so happy with the change. My workouts are not suffering and I have leaned out. I actually feel like I have more energy.

    1. Coming from the Leangains approach are you doing the 10g of BCAA a couple of times between your crossfit session and your fast breaking? It sounds pretty similar to my situation but I’d prefer not to supplement but worry that I’m doing more harm then good by working out mid fast.

  40. Thanks for the insight Mark..glad I came across your blog. Running is what I have done for the past 20 years. I certainly feel your post makes a great deal of sense. I have done some of my best long runs without even eating breakfast…did a 20 miler in 1.50.02 (5.30 aver. per mile) on water alone…more running coaches are gearing more to depletion type efforts to teach the body to run with less in the tank.

  41. The thing I don’t get is the absolute fastest any protein food can be digested is about 1.5 hours, with many types of proteins being significantly longer. I would imagine most fats except coconut oil would be similar. So setting aside BCAA that might be absorbed fast, if you drink a pre-workout (low carb) protein shake, would that break a fasted workout? It seems the nutrients wouldn’t really hit until after the workout. And if you want to make sure the nutrients hit right after, you should drink it about an hour before exercising? thoughts?

    1. In my case I’m talking about a 20 minute HIT weight lifting session.

      1. Btw, does anyone else get muscle cramps at times? I’ve noticed since I started eating Paleo lowish-carb and started doing high intensity exercise like sprint intervals and HIT lifting that I get calf cramps sprinting, toe and calf cramps from the leg press, and minor forearm cramps from doing pulldowns and deadlifts.

        1. I am also curious about the increase in tendency for cramps. Is it due to the primal diet or perhaps have I become deficient in some mineral/nutrient due to cutting so many carbs( limited veggies/fruits as well for Ketosis).

        2. I’m kind of the opposite. I used to get cramps every time I would play a soccer or ultimate frisbee game. Every time! And I used to stretch beforehand every time.

          I stopped stretching. I’ll just do one of the low super-squat stretches for a good 30 seconds or so before I do anything active. My legs seem good to go. I haven’t had a single cramp since going Primal and dropping ‘standard’ stretching.

          Some suggestions are to be sure you are hydrated. Squeeze a lemon or lime out into some water and put 1/8 or 1/4 tsp on salt in there and shake it up. This is basically a home made gatorade. I drink this usually 2 or 3 times a week. It may have something to do with the lack of cramps. I also eat plenty of fruit and some starchy foods (wild rice, sweet potatoes) most days out of the week.

  42. Those of you experiencing dizziness, light-headedness and headaches during fasting period might consider increasing your salt/mineral intake by drinking a few cups of boullion during the day.

    Your body will use water more efficiently during carbohydrate restriction and will tend to shed it along with the minerals which will cause the above symptoms.

    Alternatively you could make your own bone broth on the weekend (a gallon or so) to be consumed throughout the week. In this case, you can of course make use of sea salt.

    This subject is treated extensively elsewhere on this website as well as in “The Art and Science of Low Carbohydrate Living” by Stephen D. Phinney und Rd Jeff S. Volek

  43. Should fasting be considered when you try to GAIN weight? Right now I am actually eating 3 meals a day and exercise 2-3 time (LHT), sprints once a week and of course of lot of walking – in order to gain some weight.
    What do you think of that?

  44. Hey Mark – I’ve not fasted for a while but I have worked out fasted in the past and it’s worked fine for me. I didn’t really see any massive improvements in my performance compared with working out after a meal but I didn’t suffer either.

  45. As mentioned at the tail end of you article – I have definitely benefitted from strength training on an empty stomach in the past. Both my squat and deadlifting PR’s have been on a fasted saturday session.

    I get the feeling this is due to the body not having to ‘split focus’ on digesting and strenuous physical activity but have no hard evidence – thoughts?

  46. Mark, here’s my story.

    I’m in IT but at night/weekends I’m a recreational rock climber. I climb at a 5.10+ / 5.11- level and I’m 290 pounds.
    Let that soak in for a sec 🙂

    Prior to going on the Paleo Diet + IF in January 2012 I weighed 340 pounds and I was climbing at a 5.10 level (not 5.10+). I always ate before I went climbing and I felt sluggish.

    Now I often go to the gym in a fasted state and I find that climbing in a fasted state vs. full/happy tummy is interesting, I can push harder for longer fasted than not.

    I’m also finding that some of the more challenging climbs (5.11/5.11+) are starting to seem easy and I’m actually getting off the ground!

    Imagine doing a pullup on a rock the thickness of a credit card AND you weigh 290…

    Anyways I think there’s a lot more to Paleo + IF + Bulletproof + 4hrbody than we even know.

  47. I love fasted training. My only concern is the timing of everything – I typical use an eating window from 12:00-8:00 pm, however my only chance to consitently lift heavy is first thing in the morning (6:00 am). I don’t mind working hard fasted and I feel great doing it but I feel almost ‘obligated’ to eat afterwards which would require shifting my window which wouldn’t really work for me.

    Anyone have experience training mid fast instead of ending one with a workout? I’d be interested to hear others experiences.

  48. Thanks to these articles I’ve started fasting one evening a week (am taking it slow!).

    Am amazed at how easy it is (been primal for a year) and how I actually now really look forward to doing it. I love the feeling of calm contentment it gives me and the wonderfully refreshing sleep it produces. I feel like it gives me a weekly ‘reboot’. The more I adhere to the primal principles the easier it is. Who knew fasting could be so enjoyable?!

  49. I’ve technically been fasting for about half my life (running late for school and not eating until I got home most days) and I can definitely confirm that my performance suffered back then.
    It does not now so food choices do affect the efficacy of fasting.
    Also, I find that my training is definitely better fasted.

  50. “Right off the bat, then, I’ll say this: don’t even consider fasting and training if you’re not going to become fat-adapted.”

    Good Lord, this is ridiculous. I stopped reading after this statement.

  51. i was wondering about thisstatement…10 grams of BCAA (branch chain amino acids) taken before the workout should boost the enhancement without taking you “out of the fast.”
    and weather or not this applies to just bcaa’s or if it would also be applicable to whey, i know ori hofmekler thinks that whey is good to have on a fast as it promotes the prduction of glutathione and therefor helps to promote cleansing but i was wondering why an ammount of protein wouldn’t take you out of a fated state via gluconeogenesis?

  52. Well I just experienced a fasting of a sort – My 2year old was hospitalized for acute bronchitis at 3am a few days ago. Breakfast that was brought to us was toast and oatmeal, of which neither of us ate. Lunch was turkey,potatoes, stuffing, bread and cake – bleh, we ate the turkey. Needless to say my daughter was hungry so she ate all her meager portion and most of mine. Then supper was ewww more potatoes, some kind of egg thing and more nasty bread. I never ate anything – not being sure of the egg thingy. Now suffice to say i the last 24 hours I had water and a slice of turkey but I had so much energy and was alert even though I was also really stressed out and sleep deprived. So I think once things get back to normal around here and we are getting more sleep, I am going to try this fasting business………….unless the feeling of energy was coming from the whiffs of epinephrine escaping my daughters oxygen mask while I held her LOL.

  53. I appreciate and thank all the gurus (Mark & Martin et. al) for taking the time and effort to expouse all of their well researched info on many topics regarding Primal, LC, IF, FT and others. It was because of them, I have turned my health around 180 degrees… So thank you again!

    Let me give you my story in a nutshell (I tried). I have been doing IF for many years without me knowing. For 15 years of working at a company I never ate breakfast and only ate lunch and dinner (12pm & 7pm). My carb/prot/fat ratio was 70/20/10 for 15 yrs. I ate lots of sugar, candy, cake, pasta, starches, white bread and 2 full bowls of rice per day. I did light weights at the company gym 3x/wk 5 hrs. after lunch. So no FT. I’m 52 y/o and my health was all borderline high BP, Cholest, & Glucose (diabetes) after all those years of abuse. I was starting to get diabetes symptoms. It was only because of my accidental IF practice that I wasn’t full blown diabetes at 52. My dad has it now.

    After 15 years of work, I got laid off. I got UI benefits for 3 yrs. and went back to school. On a low budget I then only ate 1 meal a day on good months, 2 meals a day every now and then. My IF continued. I would light weight work out first thing in the morning at 9:30am every other day with no food. I then accidentally started FT also. My diet was even more terrible with carb/protein/fat at 80/15/5 because it was cheaper. Finally my glucose spike skyrocketed one week and then I finally paid some real attention to my health and tried to figure out what was going on. I was constantly fatigued, blurred vision, dizzy, couldn’t stand up straight and was weak. Had night sweats, wouunds would take 4 weeks to heal and so on. I was skinny fat pre-diabetic and thought my life was over as I once knew it.

    I’m an Engineer by trade, so I know how to research and am very logical, analytic and calculated to a Tee. I spent 2 full weeks 18 hrs/day inbetween fatigue naps researching the internet on various topics starting with diabetes, glucose, insulin which led to low-carb, GI/GL, Bernstein, Atkins, Primal, Paleo, SouthBeach, Ketogenics, LeanGains, BodyBuilding, and many many more health topics. Remember I was desperate to get my life back and I did not believe in the existing medical system of drug induced victims it constantly generated especially with a world epidemic of diabetes that had already decided your fate from the very begining (ala Dr. Bernstein).

    After reading all of this research info I could really relate to many topics regarding high/low carbs, IF, FT, keto, metabolism, metabolic syndrom, fat gain, fat reduction and other related topics cuz I had experienced it first hand myself. But now I had become armed with the knowledge of what was all behind it. The TRUTHS behind it thanks to the contributions of all those who were willing to take the time and share with others for FREE! Thank GOD to all of you… all GOD SENDS! GOD BLESS!

    Today, I have optimized many practices from Bernstein, Atkins, Paleo, Primal, LeanGains, SouthBeach and many others. I have used a glucose meter, BP monitor, BF monitor, Chol meters, urinalysis, scales and other health analysis tools to monitor almost everything within my own documented records. All my health screen measurements have now become optimal with ZERO MEDS! My HBA1C is at 90 mg/dl, morning fast at a perfect 85 mg/dl glucose, BP at 115/83, lipid panels all optimal, resting heart rate at 51, Max heart rate at 175 during HIIT 5x per session. I do high intensity, low volume 3-5 sets staple reverse pyramid weight movements. My BF is now 10%. My benches have exeeded my highest ever during my IF training and plan to go to my genetic potential soon. My diet is now prot/fat/carb at 70/20/10 with all low GI carbs mainly fruits & veg.

    My glucose levels throughout the day range between 82-97 regardless of eating or morning fast. This is the KEY people!!! I re-carb on a daily basis up and down trying to fine tune the range tighter and tighter. This is the key for full blown 24/7 ketosis and high efficiency instantaneous hormonal releases that provide immediate fuel switching from carb to fat on a dime when initiating IF. I find my fat switch to kick in at about the 7th or 8th hr of IF which gives me 8 to 9 hrs of fat burning in one day (maybe .8 to .75 ketosis range for 4 hrs.). I got from 13% to 10% BF and gained 3 lbs. lean muscle in about 4 weeks due to tight insulin stability control while maintaining optimal glygogen levels with no dips. My goal now is to reach 7% BF and gain 16 lbs of muscle in 2 months and reach a MHR of 185 HIIT. I’m actually reversing my aging process in only 1.5 months time! At age 52 my body age tested at age 30! But remember, that I did IF by accident for many years also.

    I’ve also tested my glucose levels using a pre-workout intake of Atkins Advantage bar vs. 25g WIP (whey isolate protein) vs. nothing, 20 mins before. Glucose levels were test after IF, and 30 mins into doing a FT workout. The results are below:

    Atkins advantage bar: before 80 mg/dl, 30 mins into FT workout 109 mg/dl. Note: A moderate glucose change just bordering the high glucose levels. Felt very high energy sugar buzz almost immediately while increased reps and weight intensity. Lasted 45 mins and slowly ramped down to low levels in over an hour.

    WIP: before 88 mg/dl, 30 mins into FT workout 92 mg/dl. Note: Maintaining a perfect glucose range and almost non-effected. Felt a cellular energy response in my muscles in about 10 mins that gave me an even keel energy burn that picked up dramatically on demand when I started high intesity weights. Increased power and reps. Lasted over 2 hrs.

    Nothing: before 88 mg/dl, 30 mins into FT workout 93 mg/dl. Note: Exact same glucose results as with a WIP intake pre-workout. Did not notice any immediate energy levels. My adrenaline took about 3rd set to kick in and provide the needed energy to do high intensity weights. Endurance was not as long as with WIP or Atkins advantage bar.

    PS I also thank all of you Primal health enthusiast for all your blog inputs as they are just as helpful as the guru articles. I give it something like 70/30 guru/blog helpful ratio. THANKS ALL and GOD BLESS!

    1. Hi, Art,

      thanks for sharing your wonderful story.

      but are you sure you’re eating P:F:C of 70/20/10, or
      more likely P:F:C of 20:70:10?

      cause i think much protein can poisoning (rabbit starvation).


      1. If you re-read my story again carefully, you’ll realize I was accidentally IF (intermittently fasting) for 15 years. However my diet was carb/prot/fat ratio of 70/20/10 as I was following the USDA recommended guidelines. I even did light weight work outs 3 or 4x/wk. After 15 yrs. of this eating high GI carbs like white bread, rice, pasta, cakes, ice cream which made up the 70% daily carbs as recommended by the USDA, despite accidentally using IF, I ended up a pre-diabetic with all the full blown symptoms of a long exposed diabetic (bad limb circulation, melanin spots and patches under armpit, fatigue, dizziness, sick to stomach, neuropathy, etc…). Only because of IF, was I not a full blown diabetic with blood sugar levels at 200 mg/dl or even more! I was only running at 170 mg/dl to 200 mg/dl, which is still very high!

        With those levels, the Doctors always recommend prescribing Metformin as a basic diabetic induction until further analysis. I said “HOG WASH!!!” and never came back!

        Today after plenty of research, as that is what I am trained to do, and methodical implementation based on the scientific method of hypothesis and testing, I have come up with my own methodology to have healed my condition almost 100%! With NO MEDS! With a morning fasting glucose ave. of 85 mg/dl, a recent hba1c test of 4.8% or 93 mg/dl. A Glucose Tolerance Test of a 50g pure sugar intake took only 1.75 hrs for my receptors to take the glucose down to 120 mg/dl which is way below the standard norm in time and concentration. All signs of ZERO diabetes afterwards!

        I owe my quick (2 months) recovery capabilities from the diabetic condition I use to have, due to the accidental IF practice I did for 15 yrs., despite my carb abuse to my body. I’m 52 y/o now and my dad got it about the same age as I and his just got worse over time until he is now full blown diabetic. He however did not do any type of IF by intention or by accident. I believe that my dad and I would be a perfect real life scientific case study that would possibly show significant indicating factors in IF under similar controlled conditions.

        Anyway, today my diet consists of a prot/fat/carb ratio of 70/20/10. All my health screen indicators are optimal (BP, Glucose, Lipids, Urinalysis, Blood work etc…), I’m the strongest I’ve ever been, and yes even stronger than I was when in my 20’s when I was very very athletic. My body fat is now in the high 9% and I have gain almost 4 lbs. of lean muscle. My recovery power is even faster than when I was in my 20’s!!! I do IF every day using the most OPTIMAL techniques, where as before it was just random and by convenience and by accident. My body age tested at 30 y/o (that was about 3 wks ago). Today I have SO MUCH ENERGY that I don’t really know what to do with it. Before all this, I use to take 1 or 2 naps daily just to conserve my energy due to fatigue. Today, I get up early in the morning (sometimes I’m so rested I get up too early and have to force myself to go back to sleep) and stay up until late until 2 or 3am in the morning studying and researching cuz I have so much energy!

        During the past few months, all I do is read, read, read and study over and over again. I have obtained so much knowledge in the scientific and medical fields and have come to understand alot of the counter conflicts and controversial issues regarding many health and medical study topics. The one about too much protein being bad for you, believe me I have heard and use to believe. Too much is a relative word! Too much in respect to WHAT?!? I take just enough protein for my skeletal muscle ratio in body weight which is exactly 43% at less than 1g per muscle pound NOT BODY WEIGHT like others attest to. For me its seems to produce a perfect anabolic hormonal release that optimally grows my muscles close to 1 pound per week so far (without overdoing the caloric intake for a lean fat loss of close to .7 lbs. per wk).

        So with the given info above, the prot/fat/carb ratio of 70/20/10 can be calculated down to each respective category with carbs being the lowest. This allows me to control the caloric deficit using only carbs as the variable while keeping everything else somewhat constant. However, as I grow in muscle size and strength (which is every week), I will then adjust the protein intake accordingly while still playing with the carb variable based on any negative energy deficits or fat loss rate changes I may experience.

        Anything in over abundance yes, may be a dangerous thing! But used in a methodical manner with moderation for optimal results is the only way is should be done! Please don’t use SPECIFICALLY CONTROLLED medical studies and then paste them up as a GENERALIZATION without delving into the OVERALL facts. It’s just as bad as the spin factory with their sound bites and out of context hyperbole!

  54. Wow, thanks for the great post. Fasting and exercise doesn’t seem like they should go together. But I’m going to try this to see if it has the health benefits you describe. Thanks, Mark!

  55. Hey Mark,

    right on, brother! 🙂
    I made my serious below-10%-bodyfat improvements only once I started on the short term fasting.

    After a while you just feel great and are not hungry at all!

    And the hormonal response to the fasting is only beneficial, so it’s not only good for burning fat but for overall health as well.

    Another benefit is that you start appreciating foods once more…it’s unbelievable how tasty food can be, coming out of a 24+ hours fast! 🙂

    And imo it’s also really the natural way to eat, the body is made to run on fat for fuel much of the time, and I’m sure some medieval knight did not have a protein shake every 2.5 hours. Yet these guys were incredibly strong and big, too!

    Good to go,


  56. I was wondering what qualifies as breaking a fast? David Asprey (bulletproofexec.com) says that putting butter (grass-fed of course)in coffee doesn’t break a fast. Is this true? What about putting chia seeds in water?

  57. Mark,

    I read this article several days ago. Then today my son showed me a school report he had done on frogs based on information at https://www.sciencedaily.com/releases/2012/04/120412182332.htm and something clicked in my head. The article my son showed me posits that genetic modification happen more often in athletic frogs because after exercise free radicals are more likely to modify DNA in these frogs. The author says that this may not apply to humans, but I realized if it did it would tie your article on fasting and exercise to your article on fasting and cancer. Fasting before exercise could be beneficial (at least to frogs) because it might protect cells from the increase in free radicals following a workout similar to how it protects cells from chemo. I did a google search and found that indeed some claim that there is an increase in free radicals after exercise. Bingo.

    I never would have consider exercising while fasting before going primal. Now it is no big deal. I have been skipping lunch before workouts and following up with muscle milk and feel great.

    Thanks again for great, live changing info.

  58. I have been sugar free (some fruit) and totally grain free since April 1st, and I am having a great deal of digestive trouble. I can’t see that anyone talks about this. I also do a fast three times a week where I eat lunch, then fast until the next day lunch. My weight has not gone down and I feel like every time after I fast, I binge eat. I really feel terrible, except for the fact that I have great energy and no food cravings. Anyone have advice?

    1. AJ wrote: “I have been sugar free (some fruit) and totally grain free since April 1st, and I am having a great deal of digestive trouble.”

      By digestive trouble I’m guessing you’re referring to bowel movements… right? If so, I am experiencing the same. I’ve noticed that by eating mostly fruits and vegetable type carbs, which do contain fibers, however such fibers are sparsely thin compared to the whole grain fibers which are very dense. Stool samples are noticeably thin and pasty in comparison to the hardy and full girth stool samples when consuming whole grain fibrous carbs. It seems to create a more constipative type of bowel movement then before.

      I can’t imagine the primal Paleolithic man asking for a bathroom break in the middle of a tribal battle. He must have had to hold his movements for quite some time until it was safe and more convenient. With this type of low density fibrous diets, I find that it is very possible to do such for many hours in fact until I get home at my convenience. Where as with higher density fibrous carbs with lots of breads and cereals result in an almost instantaneous urge to follow your bowl movement regardless of what your wishes and situation may be. So you end up RUNNING to the nearest restroom or dark corner if you are nowhere near one. These type of stool are very large, hard and very dense. They cannot be stopped, halted or paused.

      Now I know we don’t have to battle for our lives on a daily basis, but I do find this a convenience. The constipation is not so fun though. So you do have options like taking a high fiber supplement like psyillium husk or inulin and you’ll be good to go.

      As far as your diet and weight loss, you’d have to be more specific about your program to really troubleshoot it. But let me take a shot in the dark since I’m already on the subject matter.

      First off, you got to make sure your DAILY average carb count is low enough even though you’re on the right track with natural primal complex carbs. Around 50g +/- 25g if you don’t work out. 50g +/- 100g if you do work out. Go to the Southbeach diet website or the Atkins diet website for a bunch of food-carb count lists to peruse through.

      You’re fasting 3x per week is ok if its all you can do. I prefer 2-3 meals in a 7-8 hr window per day, for 7 days a week. You’ll burn probably twice as much fat that way.

      If you fast 3 days in a row or close to it, it sounds like you’re trying to diet within this 3 or 4 day window with low carbs and proper nutritious food. And then coming out of it, the next 3 or 4 days you go back to a normal eating routine in which you state that you binge eat. I take it that you eat ANYTHING by the statement ‘binge’ (cookies, cakes, ice cream, etc.). It sounds like that you are being glycogen deprivated during your 1 lean meal a day program for 3 days. Then during your time off from the fast, your body then is starving for any type of glucose intake such as starch, sugars, simple carbs and such (which are very very addictive once you start with just one bite by the way). This is why you need to maintain a DAILY carb intake of 50g +/- 25g at the very least to prevent from starving your organs from the needed glycogen to function properly. If you did just that, you would NOT NEED to binge yourself after the 3 days of fasting. Your energy and appetite would have been even keel and you can then go on fasting for another 3 or 4 days. Wa-la!… the true and original IF method!

      Sorry to say, your modified method of the IF is not working for you. My suggestion is to try and use the sure fire, tried and true method that has already worked for hundreds if not thousand of people that hold personal testimony (including myself) to its effectiveness. You can’t go half ass into it and expected it to have the same results.

  59. If I’m on a long distance bike ride, I will eat just a little every hour and drink a bottle of water every hour. It allows me to finish with as much energy after my ride, as much as when I started. Nutrition is very important in long distance workouts.

  60. Art,
    Thanks for the reply! I read a bunch yesterday and am taking your advice and going with a tried-and-true method (leangains for now). I was actually doing no carbs except fruit and veggies (no grains) and no sugar except fruit and veggies, and my “binging” was fruit or other acceptable foods- just too many calories, I think. My fasts were every other day skipping dinner and breakfast. I have been having too much gas and diarrhea, for about a week- serious stomach distension! I should have been more specific, but kinda embarrassing… I am thin (125#, 5’8″, 36 year-old woman) and I crossfit according to their WOD and do 3 days on, 1 day off. I think the leangains approach might work better, but I still am really confused about all the stomach trouble.

    1. AJ wrote: “I read a bunch yesterday and am taking your advice and going with a tried-and-true method (leangains for now).”

      Good for you AJ! Just remember during your IF fasts to intake 50g +/- 25g carbs non training days, and 50g +/- 100g carbs on training days depending on your intensity and muscle size. This will keep your energy and appetite in tight even control. If you’re looking to lose weight then you can throttle the carbs down slightly until you see fat cut results. But be careful not to over do it cuz you’ll end up feeling the binge come over you. If you want to gain muscle weight, up your protein according to 1g x body weight daily. And up your carbs on intense training days to keep up with energy expending so you don’t tank out during your fasts. You will have to find your perfect balance over time and just listen to your body.

      As far as your stomach problems. I believe I understand what is happening. First off if you very rarely use to eat veggies (especially LEAFY GREEN veggies), this change over on new type of carb fuel will be new to the stomach and will take some time to adjust. Leafy greens like romaine lettuce that have lots and large leaves produce enormous amounts of carbon/methane gas when stomach acid breaks it down. You should try to mix more fibrous veggies such as broccoli, cauliflower, cucumbers and carrots into the mix. Also note that fruits and veggies contain lots of fiber in them that reduce the total net carbs that the body uses. This means you will have to consume more fruits and veggies on a daily basis just to maintain a 50g +/- 25g of NET CARBS per day to maintain proper glycogen levels for your body. Sometimes a 7-8 hr window doesn’t give me enough time to digest all those fruit and veggie fibers in large volume (especially for ectomorph type bodies like you and I. So what I end up doing is eating a couple of whole grain high carb slices of bread, or a starchy potato into the mix for the first meal. You can be creative with other options but just don’t add sugar to it cuz of the high GI spike you will get (produces hunger and energy dump in 2 hrs).

      The IF fasting method is pretty much straightforward, however, you will still have to learn alot about the fine tuning details in order to make it work optimally for use 7 days per week for the rest of your life. Just be patient cuz when you have it down pat, it will be as close as the fountain of youth and energy like you have never known before!

  61. I have been playing around with IF but I have always been way too worried about hitting a wall to exercise in a fasted state. Yesterday, because of this article, I biked to work and the gym (about 22 miles total) and lifted heavy in a fasted state.
    It was not bad at all and in fact I did not eat immediately after the heavy lifting session but waited about 90 minutes and then ate a big ass salad and then ate normally the rest of the day.
    Overall it was a great experience and I felt really good all day and feel great today.
    Six months ago I would have thought it insane to workout without eating. Thank you Mark for constantly writing such great articles that help us to push our boundaries and self experiment.

  62. I do my Crossfit workout after a 13 hr fast…I then continue on the fast for another 3 hrs or so.

    Why? Because thats when I get hungry. I refuse to shove food down my throat because I’m ‘supposed to eat XYZ’ pre and post workout.

    I feel light and focused. Afterwards I have a surge of energy lasting 2-2.5 hrs and then gradual hunger sets in…and I eat 🙂

  63. I have been fasting for nearly a month now using the 24 hour fast it’s been great though weight loss has slowed.however readin this artical has given me the spurt to carry on doing it vey interesting re weight loss and muscle retention

  64. I run and lift pre-food and never thought of it as being “in a fasted state”. But I 100% prefer working out this way. It is more convenient than trying to manage food pre-workout. I also don’t gorge after a morning run, but do succumb to protein cravings after lifting. Eggs satisfy. Now I wonder if my preference is completely psychological. In which case, may be a good idea to mix it up a bit, no? Gotta say, I have no blood sugar lows anymore and my performance has improved…speeds and recovery since I’ve been doing this.

  65. How often do you guys normally fast? Once a week? Once every 2 weeks? I’m curious. Thanks.

  66. Another issue with the Ramadan studies: Ramadan has some culture built around it, both religious and secular.
    1. Many people who are fasting are also staying up late to pray for a good portion of the night.
    2. The way people eat, unfortunately, at night during Ramadan, is usually kind of gluttonous. If you aren’t focusing on the spiritual aspect of the fast, you end up obsessing over food, which means unnecessarily full plates and desserts every night. In my experience, the food usually involves some kind of hearty stew of some kind over a heap of rice, with something fried as an appetizer, often accompanied by a soup (barley or lentil based) and then some heavy dessert drenched in simple syrup. So yeah, it’s not like the fast is being broken on fast-friendly food most of the time. Breakfasts are sleepy and rushed since they (we?) are on a deadline, so there are a lot more convenience foods involved. And yeah, a lot of people don’t take the time to properly hydrate before and after the fast.

  67. I got a question..I workout @ 2:30am. I don’t eat my postworkout meal until 10:30am. Next meal @ 1:30pm and last meal @ 5:30pm. Is waiting nearly 7hrs to eat post workout meal to long? If so how long should I wait to eat post workout meal.

  68. Hi! Does anyone know which is the best fast for a woman to lose 20-30lbs, without losing too much muscle? I need to fit back in my size 0 clothes again;-(. I believe a fast is best for me right now, because eating anything just makes me hungrier, lol. I’m 5’4, 135 lbs and want to get back to 105lbs.Lauren Los Angeles

  69. I am puzzled why so many people (mainly women) working out on cardio machines have a platic bottle of water they can and do suck during their 20 min session.

    I generally have a drink 1/2 way through a 2 hour workout spread over various aerobic exercise machines and some light weight work. This drink is at the gym bubbler. I suffer no ill effects. I enjoy a beer or two before dinner that evening.

    I thought you might have touched on the benefit of allowing dehydration for say an hour or do? Remember where we all came from 50,000 or more years ago, the flatland of Africa where lots of running was required to survive! No plastic bottles on the flatlands!


  70. I’ve done all my long marathon training runs in a fasted state. This includes a 20 miler. Had a pretty good marathon of only 8 minutes off a PR. And I wasn’t really trying for a PR. Had I not stopped for the bathroom, I would have been only 3 minutes off the PR, and, again, I wasn’t even trying.

    I like what you say about not fasting for performance but what if that’s true as well?

    The running community is or should be shocked by this guy winning the grueling Western States 100 mile race in a low-carb state. Not fasted but low-carb.I wonder if all this carb stuff for runners is a myth as well. My running coach says eating sugar during the marathon tells your muscles to dump its glycogen, obviously the opposite of what we want.


  71. I realize that this is an old post, but after looking at the research which supported the conclusions in sections “Improved Recovery from Endurance Exercise” and “Improved Glycogen Repletion and Retention,” I am really disappointed in the author. Briefly, the study “Effects of caloric restriction and overnight fasting on cycling endurance performance,” as Mark indicated, had no control group, an essential feature of respectable scientific research of this type. What’s more, cyclists lost weight with caloric restiction (no suprise), saw no difference in cycling performance, and had lower RPE (perceived exertion). One thing not mentioned which can account for most of these changes is the TRAINING RESPONSE TO ENDURANCE EXERCISE. RPE decreases with training, and other measures such as power output, submaximal exercise performance, and VO2max hopefully increase with training, though none of these were observed over the 3 weeks they spent training between the measurements. The same study could be cited to show that training under caloric restriction failed to induce beneficial training adaptations in cyclists. I don’t see how any claims for calorie restriction improving recovery or performance can be made from this study.

  72. I did not know about a fasting diet nor started for health reasons. Due to economic restrictions I cut down a lot on foods that I would normally over eat out of boredom or time of day. I noticed after cutting out sodas and junk food I lost Mabay ten or so ibs. Then fasting around a 20-36 hour period had a huge weight loss benefit. After around 7 months of fasting I lost nearly 90 ibs. I also incorporate 30 min of sprints and 30 minutes of moderate weights. During a workout I usually have an excess amount of energy but will quickly dehydrate. I found drinking one or two bottles before helped significantly and 2 after helped even more for me. As I read more about the Paleo diet the more sense it makes and the more I noticed I started to naturally shift to this diet even before I found it. I find eating most of the things I use to are now too sweet or make me physically sick.

    1. There are numerous links in the post, many of which point to research articles:

      URLs in this post:

      [1] fasting on weight loss: https://www.marksdailyapple.com/fasting-weight-loss/#axzz1rmYIj72B

      [2] adipose tissue: https://en.wikipedia.org/wiki/Adipose_tissue

      [3] increase cancer survival and resistance: https://www.marksdailyapple.com/fasting-cancer/#axzz1rnxULZRG

      [4] life extending benefits of caloric restriction: https://www.marksdailyapple.com/fasting-longevity-lifespan/

      [5] fasting may have protective and therapeutic benefits to the brain: https://www.marksdailyapple.com/fasting-brain-function/

      [6] sometimes negative results: https://www.ncbi.nlm.nih.gov/pubmed/22375237

      [7] lifting, some walking, and maybe a few sprints: https://www.marksdailyapple.com/primal-blueprint-fitness/

      [8] sleep: https://www.marksdailyapple.com/the-definitive-guide-to-sleep/

      [9] PDF: https://www.google.com/url?sa=t&rct=j&q=ramadan%20sleep%20deprivation&source=web&cd=9&ved=0CGEQFjAI&url=http%3A%2F%2Fwww.phitools.com%2Fpdf%2Froky_jsr_2001.pdf&ei=f3GGT8mSF5HJiQLck9XNDw&usg=AFQjCNEHgj5zV–yWDbzvsQDYNTgI1Xitg&sig2=D6lP6yEBza1Rco11Hx7ajg

      [10] performance of daytime tasks decreases: https://onlinelibrary.wiley.com/doi/10.1111/j.1742-1241.2005.00811.x/abstract

      [11] sleep for general health: https://www.marksdailyapple.com/poor-sleep-may-make-you-and-your-liver-fat/

      [12] inadequate sleep can also translate to poor athletic performance: https://sportsmedicine.about.com/cs/conditioning/a/aa062800a.htm

      [13] extra virgin olive oil: https://www.marksdailyapple.com/is-all-olive-oil-created-equal/#axzz1roPUzEX9

      [14] shawarma: https://www.marksdailyapple.com/shawarma-salad/

      [15] shift smoothly and easily to the fat based metabolism: https://www.marksdailyapple.com/a-metabolic-paradigm-shift-fat-carbs-human-body-metabolism/

      [16] fasting: https://www.marksdailyapple.com/health-benefits-of-intermittent-fasting/

      [17] study: https://jp.physoc.org/content/588/21/4289.abstract

      [18] improved post-workout recovery: https://www.ncbi.nlm.nih.gov/pubmed/19197210?dopt=Abstract

      [19] study: https://www.springerlink.com/content/p0n17115736tt254/

      [20] study: https://www.springerlink.com/content/w8712615714k8150/

      [21] take on the study: https://www.leangains.com/2009/12/fasted-training-boosts-muscle-growth.html

      [22] glycogen: https://www.marksdailyapple.com/glycogen/

      [23] I’ve discussed before: https://www.marksdailyapple.com/how-to-fuel-a-marathon/#axzz1rmYIj72B

      [24] study: https://www.ncbi.nlm.nih.gov/pubmed/20452283

      [25] pullups: https://www.marksdailyapple.com/how-to-proper-pullup-chinup-technique/

      [26] milk the post-workout growth hormone surge: https://www.marksdailyapple.com/post-workout-fasting/#axzz1roPUzEX9

      [27] we’re not: https://ajpregu.physiology.org/content/296/1/R29.full

      [28] sprinting: https://www.marksdailyapple.com/sprint-routine/

      [29] self experiments: https://www.marksdailyapple.com/why-self-experimentation-matters/

      [30] sprinting: https://www.marksdailyapple.com/marks-beach-sprints/

      [31] Why Fast? Part One – Weight Loss: https://www.marksdailyapple.com../../fasting-weight-loss/

      [32] Why Fast? Part Two – Cancer: https://www.marksdailyapple.com../../fasting-cancer/

      [33] Why Fast? Part Three – Longevity: https://www.marksdailyapple.com../../fasting-longevity-lifespan/

      [34] Why Fast? Part Four – Brain Health: https://www.marksdailyapple.com../../fasting-brain-function/

      [35] Why Fast? Part Five – Exercise: https://www.marksdailyapple.com../../fasting-exercise-workout-recovery/

      [36] Why Fast? Part Six – Choosing a Method: https://www.marksdailyapple.com../../why-fast-part-six-choosing-a-method/

      [37] Why Fast? Part Seven – Q&A: https://www.marksdailyapple.com../../fasting-questions-answers/

      [38] Dear Mark: Women and Intermittent Fasting: https://www.marksdailyapple.com/women-and-intermittent-fasting/

      [39] Primal Blueprint Fitness eBook, Free Health Tips and Primal Recipes: https://www.marksdailyapple.com../../feeds/

  73. do you have any tips for ramadan fasters then?
    would this work if you have a decent diet?
    i can only hydrate during the nighttime

  74. For the first time over the years, I had decided to fast during Ramadan. I was worried incase I had to miss my daily1.5 hrs to 2 hrs workouts which I love doing, inorder to preserve my energy. How was I to do excercise without a single drop of water or food from 3am to 9pm?
    I thought I could give it a try (ie exercising when fasting) and to my amazement, I actually exercise better and didn’t feel hungry or thirsty at all! I was also free of headache and could carry my daily routine effortless. When it’s time to break my fasting (around 9pm), i only need a small amount of food. I was very curioused with this discovery and looked up on the internet to find the reason why and came across this website which I found very useful. I thought I would share my experience with others.

  75. I am not Primal…Yet! I am just starting to read about it and that is how I came to these articles on Fasting.

    I am a runner. I’ve run for the past 8 years and for the past 3 years I’ve run in a fasted state. I run 30 – 40 miles a week and I am still gettting faster – even at 46. My weight stays under control ( I was 240 when I started and I’m now at 185). I think the fasting helps me to remain in a “glycogen ready” state and when I go to race and then actually eat some protein and carbs before the race I am fueled and on fire.

    I also fast on an intermittent basis and eat 2 – 5 times a day depending on how I feel. Fasting works!

    Thanks for all of the helpful info on this site.

    Run Long & Run Happy!

  76. Is this safe for anemics?

    As a muslim I can tell you that most of us eat really unhealthy, fattening food when breaking our fast (not me) and immediatly rush to smoke a ciggy as well.

  77. I have been on a good roll lately with weight training and walking. I’ve been doing the frequent small meals high in lean protein and veggies. My metabolism is ramped up. I am finding without the intense aerobic that I used to focus on that I eat frequently, yet my pants are getting loose on me which is pretty awesome. I am going to try some partial extended daily fasting, including before I lift, but, perhaps it is simply a matter of wording, one statement here is patently untrue: “Furthermore, only fasted training significantly improved muscular adaptations to training.” I make variations of this healthy stuff in bulk that includes a lot of veggies lightly cooked in purified water, centered on one bunch of organic beets, greens and all, with either brown rice or ramen soup and lean chicken or tuna. I often eat it before I lift and even have had a few spoonfuls between sets recently. Among other things, I am benching around 170 (Not sure how much the bar weighs.) twice a week. When I am on a good roll as I have been my performance often improves notably from one workout to the next and I am going to increase the weight next session. I recently went from a 12 rep max to 15 reps and the way that is stated, “only fasted training significantly improved muscular adaptations to training.” this would only have been possible if I was fasting which I certainly was not. Nit picking perhaps. In any case I am going to investigate fasting with my workouts.

  78. Does anyone have any advice on fasting before an evening workout? I always workout at 5:30 pm and I curious at what time I should stop eating before then to reap the fasting benefits. Right now I eat a small snack about an hour before my workout and I’d like to change that habit. I read somewhere that I should stop eating 2 hours before a work out. Thanks everyone!

    1. Also if it makes a difference I do crossfit workouts a few days a week and then some days I just work on strength

  79. I love working out fasted! My favorite cardio is jumping rope, when I’m in that good fasted state it’s just amazing- I feel so incredibly light, like my feet are barely even touching the ground, it feels like I could just go on forever. And how much more flexible you are in that state is something else. For me, every time I work out fasted it’s a pleasure, I don’t want it to end, but working out after eating usually feels more like a chore, I feel too weighed down and sluggish to want to keep going.

  80. I want to continue with IF 16/8 but I feel like I am fading during my swim, ride or even my run. I am trying to implement IF with my training. I usually train early in the morning, and its kind of difficult continue fasting until 3pm. Beside, changing my training for later, any other suggestions. I love the clarity and the great mood that im in. Also, loosing slowly some weight and feeling good. Dont know what to do when is time to train for more than 2 hours on the weekend. I need some fuel to keep up.

  81. I have been doing 50 mile bike rides with overnight or several day Fast’s but found when I stretched to a 100 mile distance I began to hit the wall around 60 miles needed to eat one of the prolon fasting bars to finish the 100. Was not a strong performance but I finished. Start of the ride was about 36 hours into fast. I held the fast another 6 hours and felt like I needed to break the fast at 48 hours

  82. My experience with 23-48 hour IF (female, over 40) was that my energy went up dramatically and I went from being ill and barely able to move to doing random cycles of squats and cleaning out our storage shed.

    I was attempting to do keto, but, keto as described (by mostly anyone) never worked for me. Except the way Eric Berg describes it comes close. I followed his advice to have “some fat” but not a lot, to eat 7-10 cups of vegetables per day, to get down to eating one meal per day (or, 2, if that’s what it takes to get your veggies in) and to intermittent fast. But, I definitely had more carbs than he’d ever recommend. And, I could always feel when my body was ready for carbs and couldn’t find them and then switched to burning fat. Which happened pretty quickly. Not the first day or two. That took a couple of hours of sloggishness. But, I would rest a little bit here and there, until the energy cycled back around and go some more when I went from eating to not eating.

    I found out later that if I , sometimes, resist the urge to “do” and instead I rest and remain calm, there are more healing benefits and I gain more muscle. But, if I keep busy with physical activity, I don’t lose muscle and I lose more fat.

  83. Oh, I forgot to say something.

    I quit IF for a while and tried to sort out what to do, because, I was so full of energy that I almost lost my job. I couldn’t sit still and concentrate on my work. And, I didn’t know what to do about that because, due to long term illness (Crohn’s, as it turns out) I was not structurally sound enough to start doing HIIT workouts or anything. I had more energy than I knew what to do with. That’s why I did some research and found out about, basically, enforced resting to turn the energy inward into healing.

    But, I want to lose weight. And, I have not found that balance where I can IF enough to lose weight, but, not so much that I can’t do my wage work. So I did Ayurvedic fasting, which is more about eating kitchari or something similar for a few – many days in a row. That helped me find a better energy balance. I lost weight, but, more slowly. There was not as much healing, though.

    So, I guess I need to IF on the days I am not doing my wage work and be a proper McDougaller, or something, on the days I am working. Thanks for helping me sort that out.