Recent studies of the treatment of obesity by moderate and severe caloric restriction show that patients treated in randomized trials using a conventional 1200 kcal/d reducing diet, combined with behavior modification, lose approximately 8.5 kg in 20 weeks. They maintain approximately two thirds of this weight loss 1 year later. Patients treated under medical supervision using a very-low-calorie diet (400 to 800 kcal/d) lose approximately 20 kg in 12 to 16 weeks and maintain one half to two thirds of this loss in the following year. Both dietary interventions are associated with increasing weight regain over time, although regain can be minimized with the recognition that obesity, in many cases, is a chronic condition that requires continuing care. Patients who participate in a formal weight-loss maintenance program, exercise regularly, or both are likely to achieve the best long-term results.
Thomas A. Wadden (1993) studied this question.