One of the benefits of regular exercise is that is has an appetite suppressing effect, believed to be due to an increase in leptin hormone levels during and after a workout. Leptin has been shown to curb appetite in animals as body fat increases, by shutting down appetite and encouraging physical activity. Unfortunately, obese women seem to develop leptin resistance, nullifying the effect of the hormone.
The study was conducted at the University of Michigan and was funded by the National Institutes of Health. It was conducted in order to better understand how changes in body fat levels influence leptin as well as appetite levels. Post-menopausal women, half of whom were lean and half of whom were obese, ate three weight maintenance meals per day and exercised on a treadmill in the morning and afternoon. Each burned the same number of calories, but one group worked at a high intensity level and another group worked at a low to moderate intensity.
The women reported their appetite levels on a 10 point scale, and blood samples were taken to measure leptin levels. Unlike the lean women, the obese women reported no appetite suppression during exercise. However, the obese women had much higher leptin levels than the lean women.
Katarina Borer, PhD, a University of Michigan researcher and lead author of the study, says "The hormone doesn't do the job it's supposed to do in obese people. Obesity interferes with leptin's detection of exercise energy expenditure and with appetite suppression. Obese women perhaps need to consciously watch their calories because some of the hormonal satiety signals don't seem to work as well."
Borer notes that this information will help therapists and physicians understand the limitations of exercise in appetite control for weight loss in obese people.