Exercise Reduces Hunger In Lean Women

Exercise does not suppress appetite in obese women as it does in lean women, according to a new study.

"This [lack of appetite suppression] may promote greater food intake after exercise in obese women," said Katarina Borer, a University of Michigan researcher in the Division of Kinesiology, and lead author of the study. "This information will help therapists and physicians understand the limitations of exercise in appetite control for weight loss in obese people."

The results will be presented today (June 17) at The Endocrine Society's 90th annual meeting in San Francisco.

Borer and her co-authors sought to better understand how changes in body fat level influence appetite and a hormone called leptin, which in animals curbs appetite when body fat increases. When leptin levels rise, it supposedly shuts off appetite and motivates physical activity to burn calories. However, as obese people become heavier, their leptin levels rise, but they become resistant to the actions of this hormone.

"The hormone doesn't do the job it's supposed to do," Borer said.

Borer's group studied 20 postmenopausal women: 10 lean and 10 obese women. The women ate three weight-maintenance meals a day while participating in three experiments on three separate days. During one experiment they did not exercise.

In the other two experiments the women exercised on a treadmill in the morning and the afternoon. They burned 500 calories each time. These two experiments differed by exercise intensity. One involved walking at high intensity, or 80 percent of maximal effort, for 7.5 minutes, with 10-minute rest periods between 10 walking sessions. The other experiment was half as intense (40 percent of peak effort) and involved walking for 15 minutes and resting for 5 minutes.

Every hour and before each meal, subjects recorded their appetite level on a 10-point scale ranging from not at all hungry to extremely hungry. Blood samples were collected every 15 to 60 minutes for hormone measurements.

"Obesity interferes with leptin's detection of exercise energy expenditure and with appetite suppression," Borer said. "Obese women perhaps need to consciously watch their calories because some of the hormonal satiety [fullness] signals don't seem to work as well."