EFFECTS OF FASTING AND GLUCOSE-INFUSION ON BASAL AND OVERNIGHT LEPTINCONCENTRATIONS IN NORMAL-WEIGHT WOMEN

The plasma concentration of leptin is reduced in association with chro nic energy restriction and weight loss in humans, but little is known about the acute effects of fasting and glucose infusion on leptin. In this study, plasma leptin, insulin, glucose, and fatty acid concentrat ions were measured daily in 14 healthy, normal-weight, female voluntee rs aged 24 +/- 4 y with a body mass index (kg/m(2)) of 24.2 +/- 3.6 du ring a 4-d fast. The mean plasma leptin concentration decreased by 54 +/- 8% with fasting (P = 0.0006, ANOVA). In a stepwise-regression mode l, the change in leptin concentration with fasting correlated most sig nificantly with the change in insulin (R-2 = 0.48, P = 0.0057) and to a lesser extent with the change in body fat by bioimpedance analysis ( R-2 = 0.19, P = 0.03). Plasma leptin concentrations measured every 20 min from 2000 to 0800 on the fourth night of the fast did not show a t ime-dependent rise. A continuous intravenous infusion of 5% glucose pr oviding 1414 +/- 323 kJ/d (338 +/- 78 kcal/d) was begun after 4 d of f asting in seven subjects who continued to fast for an additional 6 d. Within 24 h of the glucose infusion, leptin concentrations increased s ignificantly by 80 +/- 52% (P < 0.05). These data show the sensitivity of plasma leptin concentrations to small changes in energy supply and suggest a basic role of substrate metabolism in the short-term regula tion of leptin.