Very–low-calorie diets (VLCDs) are best used in an established, comprehensive program. VLCDs involve reducing caloric intake to 800 kcal/day or less. When used in optimal settings, they can achieve a weight loss of 1.5-2.5 kg/wk (3.3-5.5 lb/wk), with a total loss of as much as 20 kg over 12 weeks. No good-quality evidence suggests that a daily calorie intake of less than 800 kcal/day achieves any additional weight loss in the long term.