Traditional weight-loss methods include low-calorie diets between 800 to 1500 calories a day and regular exercise. An alternative method sometimes considered for significant short-term weight loss in moderately to severely obese people is the very low-calorie diet (VLCD).
What is a very low-calorie diet (VLCD)? 
VLCDs are doctor-supervised diets that provide an individual 800 calories or fewer per day. These diets typically involve the use of a commercially prepared formula, but some physicians prescribe VLCDs made up of lean protein foods. Formulas prescribed by a physician for these diets are not the same as those you can find in a drug- or grocery store. VLCDs, when used under proper medical supervision, effectively produce significant short-term weight loss in moderately to severely obese patients.
Who should use a VLCD?
VLCDs are generally safe when used short term under proper medical supervision in patients with a body mass index (BMI) greater than 30. BMI is a mathematical formula that takes into account a person's height and weight. To calculate BMI, a person's weight in kilograms is divided by height in meters squared. Use of VLCDs in patients with a BMI of 27 to 30 should be reserved for those who have medical complications resulting from their obesity. VLCDs are not recommended for women who are pregnant or breastfeeding, and are not appropriate for children or adolescents, except in specialized treatment programs. There is also little research available to support using VLCD's in people over the age of 50. The decision to treat an individual of this age with a VLCD should be made on a case-by-case basis by a physician.
People with significant medical problems or who are on medications may be able to use a VLCD, but this must also be determined on an individual basis by a physician.
Health benefits associated with a VLCD
A VLCD may allow a severely to moderately obese patient 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 improve obesity-related medical conditions, including diabetes, high blood pressure, and high cholesterol. Combining a VLCD with behavioral therapy and exercise may also increase weight loss and may slow weight regain. However, VLCDs are no more effective than more modest dietary restrictions in the long-term maintenance of reduced weight.
Adverse effects associated with a VLCD
Many patients on a VLCD for 4 to 16 weeks report minor side effects such as fatigue, constipation, nausea, and diarrhea. These conditions usually improve within a few weeks and rarely prevent patients from completing the program. The most common serious side effect seen with VLCDs is gallstone formation. Gallstones, which often develop in obese people anyway (especially women), are even more common during rapid weight loss. Some research indicates that rapid weight loss appears to decrease the gallbladder's ability to contract bile. It is unclear whether VLCDs directly cause gallstones or whether the amount of weight loss is responsible for the formation of gallstones.
Conclusion
For most obese individuals, obesity is a long-term condition that requires a lifetime of attention, even after a formal weight-loss treatment ends. Although VLCDs are efficient for short-term weight loss, they are no more effective than other dietary treatments in the long-term maintenance of reduced weight. Therefore, obese patients should commit to a long-term treatment program that includes permanent lifestyle changes including healthier eating, regular physical activity, and an improved outlook on food. Without a long-term commitment, they will regain the weight.
Source: National Institutes of Health (NIH) NIH Publication 03-3894, Very Low-calorie Diets. January 2003/Updated June 2006
