Percent body fat and lean mass explain the gender difference in leptin: Analysis and interpretation of leptin in hispanic and non-hispanic white adults

Objective: To reassess the relationship between body fat and fasting leptin concentrations comparing plasma vs, serum assessments of leptin; ratios vs . regression adjustment for body composition; fat and lean mass vs, percent body fat; and gender-, ethnic-, and age-related variations. Research Methods and Procedures: Subjects included 766 adults from the nond iabetic cohort of the San Luis Valley Diabetes Study examined at follow up (1997 to 1998). Body composition was determined by dual energy X-ray absorp tiometry. Leptin concentrations were determined after an overnight fast. Results: Pasting serum and plasma assessments of leptin were correlated wit h percent body fat to the same degree. Women had significantly higher serum leptin concentrations than men when leptin concentrations were divided by body mass index, fat mass in kilograms or percent body fat. The methodologi cal problem inherent in interpreting these ratio measures is pictorially de monstrated. In regression analysis, fat mass alone did not explain the gend er difference. However, lean body mass was inversely related to leptin conc entrations (p < 0.0001) and explained 71% of the gender difference at a giv en fat mass. Percent body fat explained all of the gender difference in lep tin concentrations in both Hispanics and non-Hispanic whites. Similar to fi ndings about gender differences, ethnic- and age-related variations in the leptin-body fat association were minimized when percent body fat was employ ed as the body fat measure. Discussion: Regression analysis and percent body fat measured with dual ene rgy X-ray absorptiometry are recommended when assessing the relationship be tween leptin and body fat. Gender differences in leptin concentrations were accounted for by percent body fat in free living (no diet control), Hispan ic and non-Hispanic white adults.