Under normal conditions, carbohydrate, protein, and alcohol are not converted to fat. Glycogen and protein stores are closely controlled, and increasing the intake of nonfat nutrients stimulates their oxidation rates proportionally. Thus, chronic imbalance between intake and oxidation of nonfat nutrients cannot lead to obesity. On the other hand, fat stores are not controlled and their capacity for expansion is enormous. Because an increase in fat intake does not stimulate fat oxidation, a positive fat balance results, which has the potential to become chronic. Obesity is therefore due to a long-standing positive fat balance, which may simply be due to a high-fat diet. The use of the fat-balance equation instead of the energy-balance equation adds another option for the treatment of obesity--that of changing the quality of the diet, ie, lowering the fat content.