It seems natural that when you exercise, you're going to get more hungry and eat more to fuel yourself. However, as The New York Times points out, that's not always the case.
When we exercise we usually want to eat to replace the fuel we burned away (and sometimes more), but it turns out that in at least two studies, exercise actually decreases hunger for a short period. The New York Times looked at studies published in The International Journal of Obesity and PLoS One to see why this was:
Their appetites were noticeably blunted by each of the interval workouts, and in particular by the most strenuous 15-second intervals... They also displayed significantly lower levels of the hormone ghrelin, which is known to stimulate appetite, and elevated levels of both blood lactate and blood sugar, which have been shown to lessen the drive to eat, after the most vigorous interval session than after the other workouts... And the appetite-suppressing effect of the highly intense intervals lingered into the next day, according to food diaries that the men completed.
That said, there's still a lot of research to do:
That conclusion would seem to be fine news for anyone hoping to deploy exercise to trim a waistline. But Mr. Sim cautions that the studies available to date, including his, are very short-term, covering only one session of the various exercise options. “Whether or not” weeks or months of intense training “would have an impact on long-term weight management remains to be determined,” he said.
If nothing else, it's a helpful reminder that your diet and exercise are closely related, and just because you work out doesn't mean you need to start eating more.
How Exercise Can Help Us Eat Less | The New York Times