PYY has a strong inhibitory effect on bone formation. Decreased PYY secretion in obese patients leads to increased BMD; increased PYY secretion in anorexia nervosa patients and after gastric bypass surgery leads to decreased BMD. Plasma PYY was negatively correlated with BMD (in anorexia nervosa patients and premenopausal athletic women) and with P1NP (in amenorrheic young female athletes). The gene discussed is PYY; the disease is anorexia nervosa.