VLCDs are commercially prepared formulas of about 800 calories that replace all usual food intake for several weeks or months. VLCDs are not the same as over-the-counter meal replacements, which are meant to substitute for one or two meals a day. VLCDs, when used under proper medical supervision, effectively produce significant short-term weight loss in patients who are moderately to extremely obese.

Studies have shown that meal replacements at higher calorie levels (800 – 1000 calories) produce weight loss similar to that seen with much lower calorie levels, probably due to better compliance with the diet. In addition, VLCDs are usually part of weight-loss treatment programs that include other techniques such as behavioral therapy, nutrition counseling, physical activity, and/or drug treatment.

Who should use a VLCD?
VLCDs are intended to produce rapid weight loss at the start of a weight-loss program in patients with a body mass index (BMI) greater than 30. BMI correlates significantly with total body fat content. It is calculated by dividing weight in kilograms by height in meters squared, or by dividing weight in pounds by height in inches squared and multiplying by 703.

Use of VLCDs in patients with a BMI of 27 to 30 should be reserved for those who have medical complications resulting from their overweight. VLCDs are not recommended for pregnant or breastfeeding women. VLCDs are not appropriate for children or adolescents, except in specialized treatment programs.

Very little information exists regarding the use of VLCDs in older people. Because people over age 50 already experience normal depletion of lean body mass, use of a VLCD may not be warranted. Also, people over 50 may not tolerate the side effects associated with VLCDs because of preexisting medical conditions or need for other medications. Physicians must evaluate on a case-by-case basis the potential risks and benefits of rapid weight loss in older individuals, as well as in people with significant medical problems or who are on medications.

Health benefits of a VLCD
A VLCD may allow a patient who is moderately to extremely obese to lose about 3 to 5 pounds per week, for an average total weight loss of 44 pounds over 12 weeks. Such a weight loss can rapidly improve obesity-related medical conditions, including diabetes, high blood pressure, and high cholesterol.

Adverse effects of a VLCD
Many patients on a VLCD for 4 to 16 weeks report minor side effects such as fatigue, constipation, nausea, and diarrhea, but these conditions usually improve within a few weeks and rarely prevent patients from completing the program. The most common serious side effect is gallstone formation. Gallstones, which often develop anyway in people who are obese, especially women, are even more common during rapid weight loss. Research indicates that rapid weight loss may increase cholesterol levels in the gallbladder and decrease its ability to contract and expel bile. The drug ursodiol can prevent gallstone formation during rapid weight loss, but is not often used for this purpose.

Maintaining Weight Loss
Studies show that the long-term results of VLCDs vary widely, but weight regain is common. Combining a VLCD with behavior therapy and physical activity may help increase weight loss and slow weight regain. In the long term, however, VLCDs are no more effective than more modest dietary restrictions.

For most people who are obese, obesity is a long-term condition that requires a lifetime of attention even after formal weight loss treatment ends. Therefore, health care providers should encourage patients who are obese to commit to permanent changes of healthier eating, regular physical activity, and an improved outlook about food.