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Anorexia, Evolution, and Ultra Training

Posted by on May 6, 2011 | 16 Comments

I’m in the process of doing periodic fasting as a training method for running a 100 mile race near the end of June.  It is a training method I’ve used in the past with great success.

The Theory

I will go about my normal training routine without eating anywhere from 12 to 48 hours before beginning exercise.  In most cases, the training involves intermediate runs of 10-20 miles.  The fasting creates a dramatic shortage of glycogen.  The result- I hit “the wall” much earlier in a run.

This has two positive training effects.  First, it mentally prepares me for the feelings leading up to and during this low point.  Being able to confidently predict the feelings helps prevent a low during races as I can consume carbs as soon as the early symptoms appear.   Second, it seems to acclimate my body to the experience, making it less severe.  I suspect it has something to do with training the body to utilize fat stores during exercise.  My physiology expert friends could probably give a better explanation.

The experience of this glycogen-depleted training run is predictable.  The first few miles goes fairly well.  At about mile five, I start feeling fatigue.  By mile eight I experience fairly significant mental fatigue.  By mile ten I’m a wreck.  This feeling usually lasts for a few miles, then slowly subsides.

The Weird Unexpected Run

Occasionally I experience something altogether different.  This happened on a training run this last week.  I had fasted for about 24 hours, eaten about 500 calories (beer, Doritos, and jalapeno peppers), slept, woke up, ran a three mile tempo run and crosstraining routine in the morning, then did a 7+ mile hard trail run later that night.  By the time I ran the evening run I had consumed 500 calories in 48 hours.  Based on previous experiences, the trail run should have been exceedingly difficult.

But it wasn’t.

It was quite easy.  I managed to maintain about an 8-8:30 pace for the majority of the run.  At about mile 5.5 I slowed down due to some mild fatigue and a sore foot.  Since the Mind the Ducks 12 hour is coming up, I didn’t want to risk injury.  Based on the effort, I should have hit a serious wall very early in the run.  Instead, I felt great.  My energy level was akin to slamming a few Redbulls 10 minutes before the run.

This isn’t the first time I’ve experienced this phenomenon.  I’ve tried to predict when it happens, but that proved to be difficult.  There does seem to be some pattern in regards to pace- the higher the pace the less likely I experience the hard crash… at least for runs under 10 miles.  I’ve never attempted a hard, long run when fasting.


I’m always curious about physiological processes, especially those that seemingly defy logic.  This fits the category.  Why did I feel so good when I shouldn’t have had enough energy reserves to run at that pace for that long and feel as good as I did.

One possible explanation popped in my head.  A few years ago, I came across a theory about anorexia.  Shan Gruisinger, PhD., a clinical psychologist, proposed a theory that anorexia may be an evolutionarily-developed genetic trait that helped primitive nomadic humans survive.

According to the theory, anorexia developed as an adaptive trait when groups of humans ran out of food in one location.  Normally humans are overcome with fatigue and obsessive hunger, which limits their ability to seek out new food sources.  We’d curl up in the fetal position and slowly starve.  People with the “anorexia” disposition would do the opposite- they would become more energetic and/or manic, have a compulsion to move, and lead the group to new food sources, thus allowing the group to survive.

Gruisinger’s theory certainly explains some common anorexic behaviors such as the compulsion to move, exercise, and food refusal.  All of these behaviors would be adaptive… if they were used to seek out and feed a group of nomads.  In modern society where food is plentiful, the behaviors are maladaptive to the point of being dangerous.


Could Gruisinger’s theory explain why I seemingly had more energy on this hard trail run?  If so, what are the physiological processes responsible for providing so much energy?  For five miles, I was running hard enough where talking was difficult.  Based on my heart rate, my body couldn’t have been utilizing fat stores during that time.  What about the genetics?  If this theory holds true, do I have an “anorexia” gene?  Based on ALL my past behaviors, I seriously doubt this to be the case.

Could this theory explain a sub-set of individuals that suffer from anorexia… perhaps anorexia athletica?  Why does this seem to affect females more than males?  Is it a case of reporting bias?  Or would women somehow be better at finding new food sources in primitive societies (foragers versus hunters), thus more likely to have survived and passed the gene via natural selection?

So many fascinating questions… so few good answers.

What are your thoughts?  Have you ever experienced something like this?  What about Gruisinger’s theory?  Does it have merit?  Share your thoughts!



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  1. TrekoBlog» Blog Archive » Fasting and Running Performance
    May 12, 2011

    […] He’s just a little crazy is all.  You can see his post HERE. […]

  2. Adam Gentile
    May 11, 2011

    Nice post. I truly believe in this type of “fasting” for training.

  3. Beiner
    May 11, 2011

    I absolutely believe that would work. We, as humans place our ability into a little box and give ourselves limits simply out of fear.

    Fred Lebow, the first New York Road Runners president and founder of the New York City Marathon, slowly weened himself off of his dependence of sleep and food by self deprivation and he claimed that his production was never better. He was free to focus on running and bettering the NYC marathon.

    I don’t think it’s crazy. I think you refuse to limit yourself and aren’t afraid to experiment.

  4. Justin Whitaker
    May 10, 2011

    Hi Jason. Dr. Guisinger presented her work in a class of mine a few years back (I studied philosophy at U Montana). (for more on her and her work).

    In general her work at the time was not getting a warm reception in the psychology community, but it made good sense to me. I’ll forward your post on to her to see if she has any thoughts.

  5. Ivar
    May 9, 2011

    If you want to learn more about the science behind fat burning metabolism I recommend the sites of “The primal Blueprint” at and “The paleo solution” at Lots of resources there about low carb eating and living. I went low carb 3 months ago and my running and cross country skiing is going great. I find I recover faster after training now that i am low carb and has completely cut grains. Training to run my first maraton this year and completed two cross country ski marathons this winter. (40 and 53 Km)

  6. Dave
    May 9, 2011

    Why fast for 48 hours if the race is less then 30?
    What are the advantages of training your body to run without food?
    I’ve never heard of fasting for running until your goofy ideas.

    • Jason
      May 9, 2011

      Dave- the goal isn’t to train to run without food, it’s to train the body to better utilize fat as a fuel source once glycogen depletion occurs in long races. The practical result is less severe “crashes” (aka- the marathoners’ wall.) The science escapes me, but I believe it causes adaptation through an increase in mitochondial size and numbers, which ultimately allows more efficient utilization of oxygen for the burning of fat during exercise.

      • Dave
        May 10, 2011

        Okay it all makes sense, it is just very new to me and it’s hard to think out of the box when you’ve been told your whole life to eat 6 meals a day blah blah..
        I like the idea of fasting to train your body, I might experiment with that this summer.

  7. Barefoot Johnny O
    May 8, 2011

    Never experienced your story. Mr’s G’s theory seems like a stretch.

    • Jason
      May 9, 2011

      JO- The theory is far from complete, but may explain the counter-intuitive effects of hyperactivity in a situation where food is scarce. I haven’t found an adequate competing explanation so far.

  8. Tuck
    May 6, 2011

    I think that running on an empty stomach would have been the norm during our evolution, not the exception. The anorexia phenomenon is likely a perfectly normal human behavior taken to an extreme.

    I think what humans eat now, a lot of carbs all the time, is the abnormal state, and I think that we’ve lost an ability that is a normal human behavior as a result.

    Sort of like how most of us can’t run barefoot all day, although our ancestors could.

    I’m performing a similar experiment with fasted training myself, and it’s been all good so far.

    • Jason
      May 9, 2011

      Tuck- keep us posted on your results. Mine have been all positive, too. My next experiment- try different forms of exercise in a fasting state.

  9. The Maple Grove Barefoot Guy
    May 6, 2011

    I practice regular intermittent fasting, where I go for 20 hours each day without eating. All of my training I do in a fasted state. I find that I get stronger as I go along. You are experiencing your body running on fat energy instead of glycogen stores. It’s not as efficient, but a far more plentiful source of body energy.

    • Jason
      May 9, 2011

      In utras, I find the fat utilization ability dramatically reduces the negative effects of glycogen depletion which seems to happen no matter how diligent I get about carb consumption.

  10. Andy
    May 6, 2011

    It’s surprisingly easy to come up with a creative way to explain how a certain behavior or trait can be explained by an evolutionary parable. Take obesity for example: a “thrifty” gene is helpful when food is scarce. On the other hand, fat people are sluggish and fairly easy prey. So which is it? Look up the aquatic ape hypothesis on wikipedia…

    A theory can start from evolution, but in order to be persuasive it has to have other stuff to back it up. I’d take this one with several grains of salt.

  11. roo codr
    May 6, 2011

    In book The Extra Mile, Pam Reed talks about her history of anorexia and her ideas about how that’s influenced her ultra running success. She says become this sort of freak of nature and that over time her body has adapted to less food needs and seems able and even content to perform with very limited fuel.