EFFECT OF FASTING ON SERUM LEPTIN IN NORMAL HUMAN-SUBJECTS

We have studied the effect of fasting on serum leptin levels in normal volunteers. Five normal-weight (BMI < 28, 2 males/3 females) and five obese subjects (BMI > 28, 2 males/3 females) were fasted (0 Kcal) for 52 h. Mean plasma glucose decreased from 88 +/- 3 to 63 +/- 5 mg/dl, serum insulin from 16 +/- 1 to 10 +/- 1 mu U/ml, plasma beta-hydroxybu tyrate increased from 0.2 +/- 0.1 to 1.8 +/- 0.4 mu mol/ml. Serum lept in levels were higher in the obese than in the normal-weight volunteer s (31 +/- 12 vs 11 +/- 3 ng/ml p < 0.01). In the obese, serum leptin d ecreased from 31 +/- 10 to 12 +/- 5 ng/ml after 52 h (-72%, p < 0.001) ; in the normal-weight it decreased from 11 +/- 3 to 4 +/- 0.5 ng/ml ( -64%, p < 0.001). Serum leptin correlated positively with serum insuli n (r = 0.51, p < 0.001) and with plasma glucose (r = 0.61, p < 0.001). To determine effects of fasting induced decreases in plasma glucose a nd insulin on serum leptin, four normal subjects (3 males/1 female) we re fasted for 72 h while their plasma glucose was clamped at basal lev els with a variable rate glucose infusion. In these volunteers, serum leptin and insulin concentrations remained unchanged. In summary, the rapid decrease in serum leptin levels during fasting indicated that le ptin release was regulated by factors other than changes in body fat m ass. The lack of leptin changes during fasting, when basal insulin and glucose levels were maintained at basal levels, suggested that insuli n and/or glucose may play a role in the regulation of leptin release.