Marks Daily Apple
Serving up health and fitness insights (daily, of course) with a side of irreverence.
12 Apr

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

You want comments? We got comments:

Imagine you’re George Clooney. Take a moment to admire your grooming and wit. Okay, now imagine someone walks up to you and asks, “What’s your name?” You say, “I’m George Clooney.” Or maybe you say, “I’m the Clooninator!” You don’t say “I’m George of George Clooney Sells Movies Blog” and you certainly don’t say, “I’m Clooney Weight Loss Plan”. So while spam is technically meat, it ain’t anywhere near Primal. Please nickname yourself something your friends would call you.

  1. 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?

    Brad wrote on April 12th, 2012
    • In my case I’m talking about a 20 minute HIT weight lifting session.

      Brad wrote on April 12th, 2012
      • 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.

        Brad wrote on April 12th, 2012
        • 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).

          Shadowfax08 wrote on April 13th, 2012
        • 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.

          Bruno wrote on April 13th, 2012
  2. 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

    Scott wrote on April 13th, 2012
  3. 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?

    Vlad wrote on April 13th, 2012
  4. 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.

    Tom Parker wrote on April 13th, 2012
  5. 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?

    Chris wrote on April 13th, 2012
  6. 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.

    Christian wrote on April 13th, 2012
  7. 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.

    Ben wrote on April 13th, 2012
  8. 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?!

    Sian wrote on April 13th, 2012
  9. 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.

    Alex Good wrote on April 13th, 2012
  10. “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.

    KC wrote on April 13th, 2012
  11. 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?

    mark wrote on April 14th, 2012
  12. 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.

    MamaB wrote on April 14th, 2012
  13. 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!

    Art wrote on April 15th, 2012
    • 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).


      Dr. Gee wrote on April 17th, 2012
      • 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!

        Art wrote on April 18th, 2012
  14. 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!

    Christine Mattice wrote on April 15th, 2012
  15. 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,


    Mark wrote on April 15th, 2012
  16. I was wondering what qualifies as breaking a fast? David Asprey ( 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?

    Ben Hirshberg wrote on April 15th, 2012
  17. 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 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.

    Craig wrote on April 15th, 2012
  18. 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?

    AJ wrote on April 16th, 2012
    • 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.

      Art wrote on April 16th, 2012
  19. 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.

    Gregg wrote on April 17th, 2012
  20. 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.

    AJ wrote on April 17th, 2012
    • 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!

      Art wrote on April 17th, 2012
  21. 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.

    spayne wrote on April 19th, 2012
  22. 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 :)

    Me wrote on April 22nd, 2012
  23. 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

    Greg wrote on April 25th, 2012
  24. 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.

    Robin wrote on April 29th, 2012
  25. How often do you guys normally fast? Once a week? Once every 2 weeks? I’m curious. Thanks.

    jay wrote on May 9th, 2012
  26. 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.

    Summer wrote on June 10th, 2012
  27. 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.

    Robert wrote on July 16th, 2012
  28. 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

    Lauren wrote on October 9th, 2012

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