Does exercise make you hungry?

Thanks to MM, I now have the full text of the following study.  I'm going to do a test for sharing this with y'all through Google Docs.  Please let me know if it doesn't work:


Acute compensatory eating following exercise is associated with implicit hedonic wanting for food  (I'm going to intersperse quotations from all over this paper)

The efficacy of exercise to promote weight loss could potentially be undermined by its influence on explicit or implicit processes of liking and wanting for food which in turn alter food preference. The present study was designed to examine hedonic and homeostatic mechanisms involved in the acute effects of exercise on food intake.

Physical activity is currently strongly promoted as a method of weight control. However, in some individuals, a compensatory increase in energy intake (EI) might serve as a barrier for the potential for exercise to promote a negative energy balance [1].  Therefore, the efficacy of exercise as a successful method of weight management will vary between individuals [2]. EI is commonly put forward as the compensatory mechanism responsible for a lack of, or lower than expected, exercise-induced weight loss. 

Bottom Line:  Like most things, there's a high degree of individual variability and this depends on more than just physiological homeostatic signalling. 

24 healthy female subjects were recruited to take part in two counterbalanced activity sessions; 50 min of high intensity (70% max heart rate) exercise (Ex) or no exercise (NEx). Subjective appetite sensations, explicit and implicit hedonic processes, food preference and energy intake (EI) were measured immediately before and after each activity session and an ad libitum test meal.

The protocol is shown below:

Two groups of subjects were identified in which exercise exerted different effects on compensatory EI and food preference. After exercise, compensators (C) increased their EI, rated the food to be more palatable, and demonstrated increased implicit wanting. Compensators also showed a preference for high-fat sweet food compared with noncompensators (NC), independent of the exercise intervention.

Sweet fats seem to be an achilles heel for lots of people.  Think ice cream!  Another way to look at this is perhaps those who prefer this sort of food tend to compensate in some sort of "reward" means.

Exercise-induced changes in the hedonic response to food could be an important consideration in the efficacy of using exercise as a means to lose weight. An enhanced implicit wanting for food after exercise may help to explain why some people overcompensate during acute eating episodes. Some individuals could be resistant to the beneficial effects of exercise due to a predisposition to compensate for exercise-induced energy expenditure as a result of implicit changes in food preferences.

So how many are we talking about?  Well here's the graphic for all the participants and caloric compensation:

Note that the ad libitum test meal "consisted of cheese salad sandwiches, ready-salted crisps and fruit yoghurt. The average percentage energy provided by protein, fat and carbohydrate in the test meal was 13%, 45% and 42% respectively."

The groups all expended ~150 cals in their exercise bout.  The zero line indicates no change in intake and the dashed line is the "break even" point for increased intake to negate energy expended.  Out of 22 participants, I think it's fair to say that 8 or 9 essentially made no compensation at all.  Thus about 40% of folks have no effect of exercise on intake and would lose weight by exercise alone.   The authors used the 0 line to delineate 11 compensators from 11 non-conpensators but the intake difference of at least two C's is negligible.  I think this is a bit deceiving when one sees how close 2 compensators are to that zero line.  A 13/9 split seems more reasonable to me.

Another 2 compensated only to negate the increased expenditure, and 2 more increases intake by only around 100 cal and another 2 by about 150 cal - not a lot of high fat sweets needed!   These 6 would probably benefit from exercise for weight loss with just a little attention to intake.  Don't eat ad libitum from relatively high energy density foods (high fat and carbs all).  Perhaps eat some veggies or real fruit and leave the crap alone.

Then there's the 5 who overcompensated to varying more significant degrees +200 to +500 from break even and net +350 to +650 cals.   Again, if they're eating ad libitum from crap like that offered, this is no surprise.  Have a normal low carb or low fat or whatever your weight managing real foods meal, and perhaps exercise a little portion control.

But we also see that even with that crap test "meal", 3 of 22 significantly decreased intake.  Now it is fair to point out that more participants overcompensated than undercompensated, but given the food choices, all this study ultimately demonstrated was that roughly one quarter of the women will overeat SAD foods following exercise.  A full 50% were no hungrier for SAD crap after exercise than before, and some were significantly less hungry.

Thus Gary Taubes' assertion that all exercise does is make you hungrier and essentially that this is all a homeostatic reaction is wrong.