SERUM LEPTIN IN RELATION TO RESTING ENERGY-EXPENDITURE AND FUEL METABOLISM IN OBESE SUBJECTS

OBJECTIVE: Leptin is the product of ob gene shown to regulate body fat in mice. It is produced by human adipose tissue as well. but its phys iological functions in man are not known. We explored if there is a re lationship in obese humans with serum leptin and energy and fuel metab olism. DESIGN: Cross-sectional study including 45 obese (10 men, 35 wo men; age and body mass index: 42+/-7 y and 35.1+/-3.6 kg/m(2), respect ively). MEASUREMENTS: Food intake by a four-day-food record, blood sam ples for serum leptin concentrations and resting energy expenditure by indirect calorimetry. RESULTS: Leptin concentrations showed an invers e association (adjusted for fat mass, age and sex) with resting energy expenditure, respiratory quotient and carbohydrate oxidation rate (r= -0.324, P<0.05; r=-0.420, P<0.01; r=0.478, P=<0.01, respectively), and interestingly, also with dietary fat intake (unadjusted r=-0.30. P<0. 05). Especially, leptin concentrations were elevated in those with low resting energy expenditure and respiratory quotient (below the median ). CONCLUSION: Serum leptin concentrations in obese subjects showed an inverse association with resting energy expenditure, respiratory quot ient and carbohydrate oxidation rate. The physiological significance o f these associations is unclear at the moment but could indicate that obese subjects show resistance to the actions of leptin also outside t he brain in terms of regulating metabolic rate and fuel metabolism.