Very Low-Calorie Diets

A very low-calorie diet (VLCD) is one that, as its name suggests, is extremely low in calories, lower than is generally required by adult humans. While all diets typically restrict calories, a VLCD is one that restricts patients to 800 or less kilocalories per day. Following a VLCD scrupulously can result in rapid weight loss up to two kilograms or more (three to five pounds) in adults on a sustained basis (VLCDs should not be used for children). A medical practitioner will recommend a VLCD to a patient who is morbidly, perhaps dangerously, obese whose health would improve from rapid weight loss. VLCDs are particularly useful in the case of patients who have Type 2 diabetes and who are obese. The diet can rapidly reduce problems with glycemic control and this leads to swift weight loss. However, in the case of these patients and others, there are heightened risks arising from the regimen.

Humans derive their energy from food and the amount of energy, hence food, required per day varies considerably based on the size and age of the person concerned, his or her general health, and the type of diet and exercise he or she customarily pursues. Because of enhanced agricultural productivity, economic development, and changing lifestyles, many people take more food than they need. In developed countries, particularly in urban populations, obesity has emerged as an increasingly important phenomenon. Eating less and exercising more works as a corrective lifestyle for some but not all people. In extreme cases, VLCDs are indicated. They customarily consist of around 800 calories of food energy per day, which is almost certain to reduce weight for any adult. Nutritionists have designed a series of different powders which are designed not just for the energy freight they contain, but also provide a balanced diet with respect to such necessary components as protein, vitamins, fatty acids, and various trace elements. The powders [Page 776]are intended to be rehydrated by mixing with water or another suitable liquid and form the totality of the daily intake of food. Initially, weight loss results primarily from the elimination of excess liquids, but more sustainable weight loss soon follows. Alternatives include bars and these, like powders, are usually made available on a commercial basis. VLCD products should be distinguished from meal-replacement products which may appear to be similar but which are not intended to represent the entirety of a person's diet. The dangers of a VLCD are such that they should only be followed under medical supervision. Doctors will wish to calculate body mass index (BMI) before deciding whether a VLCD is suitable. Because the diet reduces both body fat and lean body tissue, it is rarely, if at all, appropriate for adolescents or elderly people.

Eating less and exercising more does not work as a corrective lifestyle for everyone. In extreme cases, very low-calorie diets are used.

Health issues that might arise as a result of a VLCD include not just the loss of needed lean body tissue, but also the effect on the brain, which will adjust its level of action to a drastically reduced intake of food energy. In addition, the loss of trace elements, which is very difficult to provide in a VLCD on an individualized basis, can result in such problems as loss of menstruation, osteoporosis, depression resulting from lack of serotonin, problems with the gall bladder and the liver, and a range of other side effects. Less serious but still potentially debilitating side effects include nausea, diarrhea, and feelings of torpor. Studies suggest that sustaining a VLCD for as long as six months can result in a loss of as much as 25 percent of body weight. Unfortunately, it appears that in common with most severe weight reduction programs, VLCDs are subject to the law of diminishing returns, that is, the longer they are pursued, the less effective they become, and if pursued beyond their effective range, weight regain may even occur. Adult obesity generally results from a complex combination of factors which require, in the long term, behavior modification and lifestyle restructuring (i.e., in terms of physical rehabilitation and exercise) in order for sustainable and positive health outcomes to be achieved.

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