Heavy snacking after exercise may have little to do with hunger or appetite hormones. In a new study, people who rode a bike for an hour ate more for lunch than those who just sat around ate, despite similar levels of hunger and short-term appetite-suppressing hormones. The urge to gobble after exercise, it turns out, may be a more complicated mixture of psychology and body chemistry.
Hoping to get a better sense of why many people chow down after an hour at the gym, graduate student Cátia Martins of the University of Surrey, U.K., and colleagues recruited 12 adult volunteers with normal weight and eating habits, half of them male and half female. The team then divided the volunteers into two groups. Both groups drank a cup of hot chocolate for breakfast, but 1 hour later, volunteers from one group took a moderate 60-minute spin on a stationary bike, while volunteers in the other group sat around reading or writing. At the end of either activity, the researchers provided both groups with identical buffet lunches of unlimited sandwiches, fruit, cake, cookies, and yogurt. At various points throughout the experiment, Martins and her colleagues collected blood samples from the subjects and had them fill out a questionnaire about their hunger.
During their workout, the exercisers reported less hunger than the inactive volunteers and had elevated levels of PYY, GLP-1, and PP, hormones that suppress appetite in the short term. By lunchtime, both groups reported similar amounts of hunger, and both had indistinguishable levels of the three hormones. Yet the exercisers out-ate the slackers, consuming nearly 20% more calories at lunch. "There is no physiological reason for people to eat more right after exercise," says Martins, who reports the findings in the May issue of the Journal of Endocrinology. Instead, she says, psychological factors or slower-acting hormones, such as leptin, may play a role. Nevertheless, short-term exercise appears to have its benefits, as the exercising group--despite pigging out at lunch--still experienced a net calorie loss due to their workout.
Exercise researcher Neil King of the Queensland University of Technology in Australia says the study is novel, but he speculates that taking blood samples right before lunch may have interfered with the volunteers' appetites.