Metabolic aspects of a protein-sparing modified fast in the dietary management of Prader-Willi obesity.

Four adolescents or young adults with the Prader-Willi syndrome (hypotonia, mental retardation, hypogonadism and obesity) received a protein-sparing modified fast consisting of 1.5 g of meat protein per kilogram of ideal body weight and meeting vitamin, mineral and fluid requirements. Evaluation of nitrogen and energy metabolism revealed the development of starvation ketosis and a positive nitrogen balance. Serial whole-body potassium measurements in two patients confirmed preservation of lean tissue despite continuing loss of weight. Clinical diabetes mellitus in two subjects was rapidly ameliorated by the regimen. Short-term weight loss greater than 18 kg occurred in three of the four subjects, and reduced weight persisted during observation periods of 26 to 44 months. This degree of outpatient diet adherence by mentally deficient subjects, who do not normally experience satiety, suggests that hunger is eliminated or at least reduced by modified, protein-sparing fasting.