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. 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!


    Peter Palethorpe wrote on October 12th, 2012
  2. 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.

    tom wrote on October 24th, 2012
  3. 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.

    Kevin wrote on December 25th, 2012
  4. 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.

    Quintin P. wrote on March 23rd, 2013
  5. Please advise references cited.

    Melissa wrote on June 23rd, 2013
  6. 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

    K wrote on July 8th, 2013
  7. 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.

    Zu wrote on July 11th, 2013
  8. 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!

    Sean wrote on October 3rd, 2013
  9. 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.

    Zee wrote on February 19th, 2014
  10. 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.

    Mike wrote on July 31st, 2014
  11. 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!

    Jessica wrote on December 12th, 2014
    • Also if it makes a difference I do crossfit workouts a few days a week and then some days I just work on strength

      Jessica wrote on December 12th, 2014
  12. 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.

    Kristi wrote on June 25th, 2015

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