Dietary and lifestyle factors in relation to plasma leptin concentrations among normal weight and overweight men

OBJECTIVE: Leptin, the product of the obesity (ob) gene, is a multi-functio nal polypeptide that is important in energy metabolism, which is strongly c orrelated with body fat mass and body mass index (BMI). In a recent prospec tive study, we found that leptin was positively associated with 4 y weight gain among overweight and obese men. This suggests that leptin resistance, marked by hyperleptinemia among obese subjects, may be an important marker for weight gain. The purpose of this study is to evaluate whether modifiabl e dietary and lifestyle factors are associated with plasma leptin concentra tions among US men. METHODS: We included 268 men aged 47-83 y(who were free of cardiovascular d isease, diabetes mellitus and cancer, except nonmelanoma skin cancer) from the ongoing Health Professionals Follow-up Study. These subjects completed a detailed dietary and lifestyle questionnaire (including cigarette smoking , alcohol drinking and physical activity) and provided a fasting venous blo od sample in 1994. All blood samples were stored in a deep freeze (- 70 deg reesC) for 4-5 y before being analyzed. Plasma leptin concentrations were m easured by radioimmunoassay. RESULTS: Men in the highest quintile of plasma leptin (mean = 14.4 ng/ml) w eighed more, were less physically active, and had higher total and saturate d fat and cholesterol intake than men in the lowest quintile (mean = 3.0 ng /ml). Physical activity and current smoking were inversely associated with plasma leptin concentrations (P<0.001). A 20 MET difference in physical act ivity per week (equivalent to approximately 3 h of jogging) was associated with 0.38 - 0.58 ng/ml lower plasma leptin concentrations for normal weight and overweight men after adjusting for total energy and fat intake, BMI an d other confounding variables. Total fat and monounsaturated fat intakes we re positively associated with plasma leptin concentrations even after adjus ting for BMI and other confounding variables; however, this association was limited to men of normal weight (BMI<25 kg/m(2)). CONCLUSION: These data suggest that physical activity may be a significant determinant of plasma leptin concentrations in men. Increasing physical act ivity is associated with lower plasma leptin concentrations even after adju sting for BMI. Physical activity may lower leptin concentrations not only d ue to decreased body fat mass, but potentially through an increase in lepti n sensitivity.