The reduction of the total fat content of ad libitum diets produces weight loss in both the short term and over periods as long as 7 years. A fat-reduced diet, combined with physical activity, reduces almost all risk factors for cardiovascular disease and reduces the incidence of type 2 diabetes. The combination of reduction of dietary fat and energy, and increased physical activity has been shown to reduce the incidence of diabetes by 58% in 2 major trials. In post hoc analyses, the reduction in dietary fat (energy density) and increase in fiber were the strongest predictors of weight loss and diabetes-protective effects. LOW-GLYCEMIC INDEX AND HIGH-PROTEIN DIETS: It remains to be shown whether a low-glycemic index diet provides any benefit to weight control beyond this. Low-carbohydrate diets may be an option for inducing weight loss in obese patients, but a very low intake of carbohydrate-rich foods is not commensurate with a healthy and palatable diet in the long term. However, there is evidence that increasing the protein content of the diet from 15% up to 20%-30%, at the expense of carbohydrates, increases the satiating effect of the diet, and induces a spontaneous weight loss, and this could turn out to be a preferred option for patients with metabolic syndrome and type 2 diabetes.