Certainly there have been many studies, as Sean Duggan referenced, asserting appetite-inhibition effects of exercise. I have never seen much more than educated speculation as to the root cause (e.g., certain hormone levels). For example, according to a paper by David Stensel published in Annals of Nutrition and Metabolism:
by which acute exercise suppresses appetite are not fully understood
but may involve lowered concentrations of ghrelin
and increased concentrations of satiety hormones, notably
peptide YY and glucagon-like peptide 1.
But as Sean says it is usually more a delay since your body will eventually need to find replacement calories to fuel it. My experience is mostly with runners, bikers, and swimmers (and mostly semi-competitive). I've found that for about a half hour to an hour after exercise those people typically don't want to eat. After that delay of course you want (and need) food. As a marathon runner, I have found that how much I eat scales like this:
- Not Running (X)
- First Two Months Getting Into Shape (0.8*X)
- Steady Routine (1.5*X)
- Running 45-75 Miles/Week (3*X + X * (Miles - 45) / 10 ).
Keep in mind that scale is personal and not a one size fits all. So I think that yes even on a whole I eat less in the first two months of running than with no exercise but after that the only appetite-inhibition seems to be the delay.