Changes in energy expenditure and substrate oxidation resulting from weight loss in obese men and women: Is there an important contribution of leptin?

The aim of the present study was to determine the impact of weight loss and its related metabolic and hormonal changes on resting energy expenditure ( REE) and substrate oxidation. Forty subjects (16 men and 24 women) took par t in a 15-week weight loss program that consisted of drug therapy (fenfluta mine, 60 mg/day) or placebo coupled to an energy restriction (-700 Cal/day) . Subjects mere asked to come to the laboratory after an overnight fast for an indirect calorimetry measurement before and after weight loss. Fasting blood samples mere also drawn and were analyzed for plasma glucose, insulin , leptin, and free fatty acid determinations. This program reduced body wei ght by 11% and 9% (P < 0.01) in men and women, respectively. Fat mass (FM) and fat-free mass (FFM) were also significantly reduced in both sexes. A si gnificant decrease in REE (13%; P < 0.01) and fat oxidation (11%; P = 0.08) was observed in men in response to this program, whereas no significant di fferences were noted for these variables in women. In men, positive correla tions were found between changes in FFM and energy-related variables, where as the best predictor of changes in REE and substrate oxidation was the cha nge in FM. in women. The most important finding of this study is that in me n, the association between changes in fasting plasma leptin and changes in REE (r = 0.50; P < 0.01) and fat oxidation(r = 0.63; P < 0.01) persist afte r correction for changes in body composition. These results suggest that a comparable weight loss is accompanied by a greater decrease in REE and subs trate oxidation in men than in women, and that these changes are better exp lained by changes in leptinemia in men and by changes in FM in women.