Endocrine abnormalities of obesity.

Studies have shown that patients with central obesity have increased cortisol secretion, probably because they have increased activity of the hypothalamic-pituitary-adrenal (HPA) axis. A high waist-to-hip ratio (WHR) is associated with low production of sex steroids, such as testosterone in men, and a low rate of secretion of growth hormone. High levels of cortisol and insulin combined with low levels of growth hormone and sex steroid can cause lipid accumulation. These hormonal changes probably produce more deposition of visceral than subcutaneous fat. Patients who are deficient in either testosterone or growth hormone show a reduction in visceral adiposity when their hormone levels are normalized. Stress has been shown to activate the HPA axis and may cause the hormonal changes associated with obesity. Individuals with elevated WHR have indications of high levels of stress and anxiety. Monkeys that were stressed by social disruption were found to have increased cortisol levels and low sex steroid levels. Many of these animals had insulin resistance and visceral adiposity. Stimulants, such as alcohol and smoking, also increase the activity of the HPA axis.