Low-calorie diets involve reducing daily caloric intake by 500-1000 kcal/day, to a level of 800-1800 kcal/day. These diets are associated with a mean weight loss of 0.4-0.5 kg per week (1-2 lb/wk). In ideal settings, the total loss can be 5-10% of starting weight (10-20 lb for a 200-lb person) over 3-6 months, occasionally higher if the individual is very successful.

With any low-calorie diet, maintaining an intake of protein with a high biologic value of 1-1.5 g/kg of adjusted body weight (adjusted body weight = ideal body weight + one-quarter of the excess weight) is vital to preserving lean body mass. Reducing intake to less than 1200 kcal/day while keeping the amount of protein at 15% may lead to protein malnutrition and significant muscle mass loss. For example, for a person following a 1200 calorie diet and aiming to consume 25% protein, the goal should be 300 kcal/day of protein (75 g).

Major potential complications include the following:

• Vitamin deficiency;
• Starvation ketosis;
• Electrolyte derangements;
• Cholelithiasis.