Every time Mati Benvenisti, an amateur athlete from the Krayot region near Haifa, runs a marathon, he can’t eat a thing for at least four hours after he’s done. Benvenisti says that his lack of appetite gets still stronger after he finishes Half-Iron Man competitions (swimming 1.9 kilometers, bicycling 90 kilometers and running 21 kilometers).
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“At times like that, I can’t eat anything until evening,” he says. Benvenisti doesn’t know why he gets the feeling of slight nausea that prevents him from putting anything in his mouth after intensive physical exertion, but he guesses that it has has to do with “some defense mechanism of the body.”
A study conducted by researchers at the School of Sport Science, Exercise and Health at the University of Western Australia confirms that this mechanism can lower the number of calories an athlete consumes after activity. But it also suggests a new theory that intensive exercise could depress appetite for a full 24 hours and even longer, thus reducing the general number of calories consumed.
The study, which was published several weeks ago in the International Journal of Obesity, investigated the influence of intensive exercise on 17 sedentary, overweight men.
The participants in this small-scale study were asked to eat after four 30-minute periods. During the first period, which served as a control, they rested. During the second period, they pedaled on stationary bicycles at a moderate rate. During the third, they pedaled at high intensity, with intermittent rest periods. In the fourth, they pedaled as intensively as they could, with intermittent rest periods.
To check whether the men’s appetites had been affected by the exercise, they were given a liquid meal of about 267 calories after every session, and 70 minutes later they were offered as much sweetened oatmeal porridge and told to eat until they felt satisfied.
Unlike the conventional wisdom that intensive exercise, which burns more calories than usual, is followed by ravenous hunger, the study found that calorie consumption after high or very high-intensity exercise is significantly lower than after a rest period.
How much lower? After half an hour of rest, the men ate 764 calories, while after high-intensity exercise they ate only 594 calories. A similar picture emerged when the researchers compared the level of appetite after moderate exercise with the level after high-intensity exercise.
Another surprising statistic resulting from the study showed that lower calorie consumption continued the day after exercising as well. According to the researchers, the men who participated in the study ate fewer calories even 24 hours after they had exercised, and did not overindulge.
According to sports nutritionist Yael Rotem, this is a fairly well-known phenomenon. “It was found years ago that hormonal changes occur in the body after intensive exercise,” she said. “Some of those changes are directly connected with the regulation of appetite.” Rotem says that one of the main reasons for the significant decrease in appetite after exercise is reduced activity of ghrelin, a peptide hormone that is known to encourage appetite and regulate weight. “On the other hand,” she says, “there’s an increase in the hormonal activity of the appetite depressors GLP and PYY. The level of intensity definitely plays a significant role.”
Rotem, herself an amateur athlete, says that the phenomenon affects her as well: after exercising, she has difficulty developing an appetite. She reports feeling slight nausea reminiscent of feelings of excitement, but in her work she has encountered people who have a tendency to vomit after intensive exercise.
Many athletes claim that the problem is not as severe in bicycling as it is after hard long-distance running. Studies conducted several years ago support the claim and indicate that the shake-up the body gets during running, together with the directing of blood from the stomach to the active muscle groups, intensifies the feeling of nausea and lack of appetite.
“Close to 60 percent of runners complain of an unpleasant feeling in the stomach during or after running,” says American sports nutritionist Marnie Oberer. “It’s not just that they feel discomfort. It can also affect their performance at one stage or another.” Amit Rozen, an amateur runner, sums it up. “That’s so right,” he says. “Many times, when I come back from training, I just have no appetite and I have to force myself to eat because I know that the body needs energy.”
Are these findings the miracle cure that overweight people have been waiting for? First, we’ll have to get many of them up off the couch to find out.