How aerobic exercise suppresses appetite

Those of you who run, bike, swim, or otherwise engage in aerobic exercise have probably noticed that in spite of burning scads of calories during your chosen activity, the last thing you feel when you’re finished is hungry. Now, researchers at Loughborough University in the United Kingdom may have discovered exactly why this is.
In a study published in the November issue of the American Journal of Physiology’s Regulatory, Integrative and Comparative Physiology, David J. Stensel and his colleagues demonstrated that 60 minutes of treadmill exercise and 90 minutes of weight training have different effects on the levels of the hormones peptide YY, which suppresses appetite, and ghrelin, the only hormone known to increase it.
The researchers discovered that aerobic exercise produces increased peptide YY levels while lowering ghrelin, leading to decreased appetite. Weight training was associated with a decrease in ghrelin, but no change in peptide YY, meaning that there was a net suppression of appetite, but not to the same degree as observed with treadmill training. In both cases, changes in appetite lasted for about two hours.
The study included only eleven subjects, and the results are subjective in that subjects were asked to rate their own hunger (not that a better means of assessing appetite exists). These subjects were all male, young (21.1 +/- 0.3 years), and fit (VO2 Max of 62.1 +/- 1.8 ml/kg/min; BMI of 23.1 +/- 0.4), so it’s not necessarily true that their subjective feelings of hunger or even their physiological responses can be extrapolated to the general population.
If there’s a practical application here, people who want to lose weight and get stronger might be advised to save the “cardio” portion of their gym work until the end of the workout in order to maximally suppress appetite.
Then again, I have a problem with the idea of working out for an hour or more and avoiding nourishment in the immediate aftermath, since this period is when carbohydrate (glycogen) replenishment in muscle can be most efficiently achieved. Whether you’re hungry or not, you should make every effort to take in 200-400 kcal worth of carbohydrates (the equivalent of a banana and a 16-ounce sports drink) as soon as you roll off the last bench or wind up your five-miler. Then, if need be, you can let your hormones go to work for you.

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  1. #1 by Norm Olsen on December 14, 2008 - 2:24 pm

    Very interesting, as I was just talking about this with a running friend. We’ve both noticed that we don’t get hungry after a long run, often not until the next day. I will pass this on to them, thanks.

  2. #2 by rjs on December 14, 2008 - 3:13 pm

    bodybuilders have known this for quite some time now. maybe not the science behind it but the results none the less.

  3. #3 by Mark on December 14, 2008 - 3:43 pm

    The article does not mention timing.
    My experience is that if I ride my bike very hard in the morning, I am not very hungry at lunch, but later in the afternoon I feel the need to eat.
    If I ride late in the day, then the “hungry period” comes while I’m sleeping, and I think this makes it easier to lose weight.

  4. #4 by Julie Stahlhut on December 14, 2008 - 6:02 pm

    I normally exercise after work; I hate exercising in the morning or at lunch time, so I work out between the end of my workday and dinner. I’ve been doing this for eleven months, by far the longest and most enjoyable exercise program I’ve ever attempted.
    I find that my appetite increases rather than decreasing after a hard workout, but two differences stand out: First, my whole body (not just my stomach) seems to crave food. Second, I’m more drawn to healthful food — vegetables, fruit, whole grains, and lean proteins — than to junk. This isn’t entirely out of character; even when I was more sedentary, the idea of eating sweets while ravenously hungry has always made me feel a little ill. But I don’t crave half a pizza, nor a Big Mac and fries, after working out. The lentil-barley stew or the steamed fish and broccoli seem much more appealing, and I can finish off dinner with a few bites of chocolate or a bowl of plain salted popcorn without feeling deprived of sugar or fat.
    My weight hasn’t changed much, but both my waist size and my cholesterol level have declined, so I assume that whatever I’ve been doing is good for me!

  5. #5 by yogi-one on December 14, 2008 - 6:12 pm

    Hmmm…this study seems to reinforce the idea that aerobic exercise should be part of a dieting program. If it is true that it suppresses hunger, and if Julie is right, increases cravings for real food as opposed to junk food, it would seem good advice to add exercise to a healthy diet for optimum results.
    Not that we all didn’t know that before this study…but if it helps you talk yourself into good eating and exercising habits, then it’s a good thing, I suppose…
    Ya gotta love it when the science supports common sense!

  6. #6 by Kevin Beck on December 14, 2008 - 6:19 pm

    I’m not sure why, but this post picked up a huge following on Reddit, where there’s a lively discussion taking place.

  7. #7 by McFred on December 14, 2008 - 6:50 pm

    Strange, that’s not my experience at all. I actually feel hungier after aerobic excercise. Maybe I am a genetic abberation?

  8. #8 by Jay on December 14, 2008 - 8:24 pm

    While this makes sense, no matter what, if you exercise you need to eat carbs, as the author said, and protein. If you want to lose fat, then work out over a longer period of time but at a lower intensity. While there is nothing wrong with working out at a high intensity your body starts to use less fat and more glycogen. Anyways, make sure you get protein to obtain the amino acids you need for the contractile proteins you just broke down, and make sure you get enough carbs to replenish blood glucose and your glycogen stores. Also I’m surprised the article doesn’t talk about epinephrine. Epinephrine is activated during short term stress aka weight lifting or even hard training aerobics. Epinephrine causes a breakdown of glycogen into glucose, increasing blood glucose, so maybe your body is trying to tell you that, hey you need to eat to replenish your glycogen stores?

  9. #9 by Pete B on December 15, 2008 - 3:50 am

    This is very interesting. I know that when I get my running up to 4-5 times a week my weight will come steadily down – but doing the sums, I’ve never been able to reconcile the weight loss with calories burned. Looks like maybe I lose weight because I eat less. Who’d have thought it!
    There’s another side as well. I don’t like running soon after a meal – and I think most people don’t. I therefore tend to consciously avoid food an hour or more before a run, so increasing the food-free window associated with exercise.
    On post-exercise food – isn’t there a shunting mechanism at work, where blood vessels around the gut close down shifting more blood to the skeletal mussels? This would mitigate against food intake immediately after a run would it not?

  10. #10 by Scott Simmons on December 15, 2008 - 11:36 am

    I definitely noticed this effect when I regularly did long-distance running workouts … One odd thing I also noticed, was that after a long swimming workout, I was always starved. I wonder what the cause of that difference was?

  11. #11 by Scott Simmons on December 15, 2008 - 11:36 am

    I definitely noticed this effect when I regularly did long-distance running workouts … One odd thing I also noticed, was that after a long swimming workout, I was always starved. I wonder what the cause of that difference was?

  12. #12 by catgirl on December 15, 2008 - 11:54 am

    @McFred:
    I feel the same way as you. After swimming for an hour, I am starving by the end of it, even if I have just eaten shortly before I started. Maybe reading about this will have some sort of placebo effect on me, and won’t be so hungry next time I go swimming.

  13. #13 by Barn Owl on December 15, 2008 - 11:55 am

    One odd thing I also noticed, was that after a long swimming workout, I was always starved.
    Distance swimming (and I rarely swim less than a mile each workout) has the same effect on me. All other aerobic activities (running, cycling, playing soccer or ultimate frisbee, cross-country skiing, equestrian sports) suppress my appetite.
    I suspect it’s largely psychological, though, as we were encouraged to eat lots of carbs immediately after competing in all-day swim meets, when I was a kid. That was some adult coach’s idea of proper sports nutrition, I guess; my parents did not encourage this at all (too late to intervene, by the time I got home). Also, a little extra pudge around the middle doesn’t have the degree of detrimental effect on swimming performance, as it does on all the other sports I listed (at least in my experience).

  14. #14 by rBST on December 15, 2008 - 12:33 pm

    This study confirms by theory that aerobic exercise supresses appetite at the biochemical level. When I take time off from running I have an increased appetite and cravings. I have to force-feed myself after long or hard aerobic workouts or I suffer the day over.
    As the above person noted, I do not feel a supressed appetite after swimming, and am, instead, ravenous. I occasionally pull myself out of the pool upon wobbly arms. The reward of a hard or long session in the pool is a sit-down at a nearby sushi bar thingy.
    Two things I’ve considered: my perceived level of exertion in the pool gets knocked off it’s usual course and I am so focused on my form (read: I am thinking harder) that I am mentally unaware of my increasing hunger. Whatever it is, I always have to eat immediately after a swim workout. Actually, I experience the same effect after playing in the ocean. Does it have anything to do with bouyancy? What happens to my internal organs when I am submerged in the water?

  15. #15 by Isolde Knaap on December 15, 2008 - 1:54 pm

    When I first read the article my immediate thought was “Is swimming aerobic?” After swimming I usually want to eat the house.
    I don’t do much body building stuff but note that aerobics in many ways decreases appetite -notwithstanding the “I worked so hard to get it off why put it back on” notion.

  16. #16 by rBST on December 15, 2008 - 2:11 pm

    “Is swimming aerobic?”
    I don’t know about you, but I am unable to breathe underwater. I suppose the answer really depends on HOW you swim. Endurance swimming doesn’t necessarily depend on speed, but in how much time you spend in the pool. But in order to swim at longer distances, much like running, you have to improve the strength, and effeciency of, muscles that help to propel you in the water. And throwing in some faster laps improves your chances of finishing the swim portion of, say, an IM without drowining. But still, yes, swimming is a form of aerobic exercise.
    Also, “I worked so hard to get it off; why put it back on” isn’t always the most rational reaction to feelings of hunger post-workout. I don’t know about youse guys, but when I am working out with the purpose of training for a race, I eat TO train, not the other way around. Starving is not an option, no matter how much more quickly I might lose angry, determined weight.

  17. #17 by Kevin Beck on December 15, 2008 - 2:17 pm

    Anything you do that gets your heart rate above about 60% of its maximum is aerobic. You can do things for an hour that aren’t aerobic (like amble at at a snail’s pace), but anything you can do for more than a few minutes can never be (predominantly) anaerobic.
    A two-minute race (be it on land or in the water) is about 50/50 aerobic/anaerobic, as assessed by fuel sources used.
    A human being can run at a pace corresponding to maximal oxygen uptake rate (“VO2 Max”) for about 10-12 minutes, which is why a properly administered treadmill test to determine the value of this parameter takes just about this long.

  18. #18 by catgirl on December 16, 2008 - 12:57 pm

    It seems that the common thread for many of the comments is that swimming might have a different effect than running on a treadmill. Maybe this should be a variable to consider in further studies, along with using a larger sample group, including women, and looking at a range of age and fitness levels.

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