The most dramatic nutritional intervention for obesity is prolonged total starvation. Because of metabolic adaptations that allow the brain to use ketone bodies rather than glucose for fuel and the conservation of body protein mass, obese persons can undergo total fasting for as long as 8 weeks, often without serious medical consequences.53 Weight reduction is marked, averaging ˜0.5 kg per day, but the costs are significant.54 Patients must stay in either a hospital or a supervised facility. They need mineral supplements, multivitamins, medication to prevent gout, and frequent observation by medical personnel.55 Besides the expense and the disruption of patients’ normal lives, the principal problem with total fasting for weight reduction is that it does not provide a mechanism for the long-term maintenance of reduced body weight. In follow-up studies, most patients return to their original weight.56

Very-low-calorie diets include a variety of regimens that commonly are structured as protein-sparing modified fasts containing 200 to 800 kcal per day, with high-protein foods or commercially available liquid protein formulas as the only source of nutrient intake. In the former, protein intake is derived from lean meat, fish, and fowl, providing 1.5 g of protein per kilogram of ideal body weight per day plus the small amount of fat contained in these foods.57 Liquid protein diets are available in several formulations that generally contain greater than 50% of calories as protein and a total of less than 500 kcal per day. As with total starvation, vitamin and mineral supplements should be provided. The rationale for these diets is that the dietary protein replaces body protein that is being degraded as a source of glucose and energy, and thereby minimizes the wasting of lean body mass. Weight loss is extremely rapid (˜0.25 kg per day).58 However, the diets carry significant risks, as evidenced by the deaths of 58 people on these regimens in 1977 and 1978.59 Although a definite link was not established between the high-protein diets and cardiac complications in the affected individuals, the most consistent pathologic finding was myocardial atrophy, a condition that also develops in protein-calorie malnutrition.60 Subsequent experience has demonstrated an absence of these severe complications with diets containing higher-quality protein, but it still is advisable to use high-protein, very-low-calorie diets only in the morbidly obese and under close medical supervision.58,61