Short- and Long-Term Changes in Serum Leptin in Dieting Obese Women: Effects of Caloric Restriction and Weight Loss¹

This study examined the effects of caloric restriction and weight loss on serum leptin concentrations in 49 obese women who participated in a 40-week weight loss program. During the first 12 weeks, half the subjects were provided a 1000 kcal/day low-calorie diet (LCD), compromised of portion-controlled foods, whereas the other half were prescribed a 1200 kcal/day balanced deficit diet (BDD) consisting of self-selected table foods. Thereafter, subjects in both conditions were instructed to consume approximately 1200-1800 kcal/day of self-selected foods, depending on their desired weight change. During the first 6 weeks, weight and serum leptin fell significantly more (P < 0.05) in women in the LCD condition than in the BDD condition. In the former group, the 55% reduction in baseline leptin was 10 times greater than the relative reduction in body weight. Stepwise multiple regression analysis revealed that degree of caloric restriction, but not weight loss, contribution significantly to the variance in the change in leptin at week 6. By contrast, long-term changes in leptin, when subjects had increased their calorie intake, were more strongly related to changes in weight and fat. At week 40, for example, weight loss account for 47% of the variance in the change in leptin. Serum leptin and body fat remained highly correlated after weight loss (r = 0.79, P < 0.001), as before (r = 0.66, P < 0.001). After treatment, however, we observed a greater-than-expected reduction in serum leptin concentrations, as expressed per kilogram of body fat. The significance of this finding remains to be determined.