To determine the optimal energy intake of very-low-calorie diets (VLCDs), 76 obese women were randomly assigned, in a double-blind fashion, to one of three liquid-formula diets: 1758 kJ/d (420 kcal/d), 2763 kJ/d (660 kcal/d), or 3349 kJ/d (800 kcal/d). Weight, body composition, symptoms, mood, and acceptability of the diet were assessed throughout the 6-mo study. There were no significant differences in weight losses or changes in body composition among the three dietary conditions at the end of treatment, nor were there significant differences among conditions in acceptability of the diet, symptoms, or mood. These results suggest that there is no clinical advantage to using VLCDs that provide less than 3349 kJ/d (800 kcal/d).