Relation between plasma leptin levels and measures of body fat in identical twins discordant for obesity

Background: Plasma levels of leptin, the recently discovered satiety hormone, are associated with adiposity in humans. Objective: To determine whether genetic factors or body fat distribution affect the association between leptin levels and obesity. Participants: 23 healthy identical twin pairs (9 male pairs and 14 female pairs, 33 to 59 years of age) who were discordant for obesity (average weight difference, 18 kg). Measurements: Pasting plasma leptin levels were measured by radioimmunoassay. Distribution of abdominal fat into visceral and subcutaneous compartments was estimated by use of magnetic resonance imaging. Results: Plasma leptin levels were threefold higher in obese twins than in lean twins (mean +/- SD, 18.7 +/- 12.5 mu g/L compared with 6.4 +/- 4.8 mu g/L; P < 0.001); a similar difference was seen when the entire study group was divided according to sex. Compared with lean twins, plasma leptin levels were 3.7-fold higher in the obese twins who had visceral fat accumulation greater than the median and 2.1-fold higher in the obese twins who had visceral fat accumulation less than the median. The intrapair differences in leptin levels correlated with the corresponding differences in percentage of body fat in women (r = 0.73; P = 0.003) but not in men and correlated with differences in visceral fat area in men (r = 0.79; P = 0.019) and women (r = 0.73; P = 0.007). In multiple regression analyses that included intrapair differences in visceral fat area and total body fat, the association between differences in visceral fat area and leptin levels was significant in men (P = 0.029) but not in women. Conclusions: Plasma leptin levels are increased in obese persons, independent of genetic background. Visceral fat may be of special importance in the regulation of leptin levels, but it is probably less important in women than in men.