Obesity is a chronic disease caused by an imbalance between the energy ingested in food and the energy expended. Enlarged fat cells produce the clinical problems associated with obesity either because of the weight or mass of the extra fat or because of the increased secretion of free fatty acids and numerous peptides from enlarged fat cells. The consequence of these two mechanisms is other diseases, such as diabetes mellitus, gallbladder disease, osteoarthritis, heart disease, and some forms of cancer. The spectrum of medical, social, and psychologic disabilities includes a range of medical and behavioral problems.