The effect of exercise on leptin concentration in healthy men and in type 1 diabetic patients

Purpose: Leptin is a recently discovered hormone that appears as a regulator of energy balance. It is important to know whether Ieptin concentrations are changed under conditions of altered energy homeostasis. Consequently, we examined the effects of exercise with fasting and exercise with feeding on circulating Ieptin concentrations in healthy men and in type 1 diabetic patients with normal body weight and well controlled diabetes. Methods: Leptin concentrations were determined with radioimmunoassay. Results: During a 3-h cycle ergometer exercise with fasting, Ieptin decreased by 42% (P < 0.01) in nine healthy men and by 23% (P = 0.05) in eight male type I diabetic patients. Leptin fell equally by 12% (P < 0.03) both in nine healthy men and in eight male type 1 diabetic patients who were studied as it resting control group. The absolute fall in leptin in healthy men was similar in the exercise and resting control groups (0.8 +/- 0.1 mu g.L-1 vs 0.8 +/- 0.2 mu g.L-1). However, due to lower leptin concentration before the exercise, the relative decrease (42%) was greater than during the resting control study (12%, P < 0.005). This difference was not seen in the diabetic patients. Fasting leptin concentration correlated positively with BMI (r = 0.75, P < 0.001) and fasting insulin (r = 0.71, P < 0.01) in healthy men as well as with insulin level (r = 0.54, p<0.05) in type 1 diabetic patients. When exercise was performed with feeding, and this was associated with a significant rise in serum cortisol level (marathon run, 14 healthy men and 7 type I diabetic patients), Ieptin concentration did not change significantly. Conclusions: I) During morning hours, Ieptin decreases both in healthy men and in type I diabetic patients, reflecting a diurnal variation of Ieptin concentration and the effect of fasting on leptin concentration. 2) The fall in leptin during morning hours is augmented by physical exercise in healthy men. 3) If exercise is performed with feeding and associated with a rise in serum cortisol level, Ieptin concentration remains unchanged. These data suggest that although exercise may reduce circulating leptin levels, the effect is small and can be counterbalanced by feeding or a rise in serum cortisol concentration.