Support: Tanita Healthy Weight Community Trust grant (2005-2006)
NIDDK grant 1 R15 DK066286-01A2
The long-term objective of this research is to arrive at a better understanding of how exercise influences the energy regulatory mechanism. The specific aims of the two proposed experiments are to test the following three hypotheses: that (1) exercise of sufficient volume and intensity will suppress appetite; (2) appetite suppression will show a positive relationship with some, or all, of the postulated endocrine mediators of satiety: hormones insulin, leptin, catecholamines, CCK, and peptide YY, and a negative relationship to the putative orexigenic (appetite-stimulating) hormone ghrelin; and (3) behavioral and endocrine suppression of appetite by exercise will be attenuated by obesity. Answers to these questions should improve currently unsuccessful strategies of combining exercise with eating to achieve body fat loss and will help reduce incidence of national obesity epidemic. The two studies recruit postmenopausal women as this demographically large group displays a high incidence of obesity and inactivity. Exercise that will cause expenditure of about 1000 Kcal in excess of resting metabolic rate is applied either at moderate intensity but with variable timing with respect to meals (Experiment 1), or at two different intensities in normal weight and obese women (Experiment 2). Behavioral measures of hunger and of satiety (fullness, desire to eat, and an estimate of quantity one can eat) are assessed hourly during daytime. Energy expenditure is assessed through indirect respirometry, and blood samples for the measurement of anorexigenic (appetite-suppressing) and orexigenic hormones are drawn at intervals ranging between 15 and 60 minutes, more frequently at the start and end of exercise and meals, and less frequently throughout the rest of the 24-h day. In experiment 1, the effects of exercise are compared under contrasting feeding conditions (exercise before or after meals). In experiment 2, the comparison entails an inactive day versus two days of exercise at different intensities (but same energy expenditure) and two levels of body fatness. In both experiments, subjects serve as their own controls. Hormone concentrations are measured by radioimmunoassays. Preliminary results in experiment 1 provide evidence for appetite suppression by exercise, but not for an effect of meal and exercise timing on the ratings of hunger, and no support for anorexigenic actions of leptin or insulin.