Hormones and body composition in humans: clinical studies

Leptin in relation to body fat and hormonal regulation of body fat distribution will be treated. Leptin circulating levels are strongly related to the percentage of body fat and in women leptin values are always twofold those observed in men. A role of androgens has been suggested to explain this gender difference. Insulin resistance may contribute to the wide variation in leptin levels. Leptin levels and insulin resistance are increased at the end of pregnancy and normalize after delivery. Furthermore, insulin resistance is associated with elevated plasma leptin levels independent of body fat mass and leptin levels are significantly related to insulin sensitivity independent of BMI. Energy restriction can strongly influence leptin levels, overcoming the effects of body composition changes. The shift from a state of triglycerides storage to a state of release could down-regulate leptin production. Triglyceride flux at the intra-abdominal level depends on the balance between insulin and corticosteroids, which have liposynthetic activity, and between sexual and growth hormones, which have lipolytic activity. Both hormonal and body composition change with ageing, primarily due to a decrease in lipolytic activity, with consequent prevalence of liposynthesis and visceral fat accumulation. Enlargement of intra-abdominal adipose cells is more gradual in men and more abrupt in women after menopause.