Very low calorie diets: their efficacy, safety, and future.

Very low calorie diets used to treat moderate and severe obesity produce average weight losses of 20 kg in 12 weeks. This paper reviews the development of very low calorie diets from research on fasting in the late 1950s and examines data on the amount of dietary protein needed to achieve positive nitrogen balance. The desirability of including carbohydrate in the diet, the choice of protein sources (formula versus animal protein), and the anorectic value of ketosis are discussed, as are patient selection and the clinical course of the diet. As contrasted to the earlier "liquid protein" diets that were associated with at least 60 deaths, very low calorie diets of high-quality protein appear safe when limited to 3 months or less under careful medical supervision. Evidence of this safety is provided by the results of 24-hour Holter monitoring and the fact that no diet-related fatalities have been reported in over 10 000 cases. The major problem to be resolved is the maintenance of the large weight losses achieved with these diets.