Very low calorie diet
Very low calorie diet (VLCD) is a diet with very or extremely low daily food energy consumption. It is defined as a diet of 800 kilocalories (3,300 kJ) per day or less. VLCDs are formulated, nutritionally complete, liquid meals containing 800 kilocalories or less per day. VLCDs also contain the recommended daily requirements for vitamins, minerals, trace elements, fatty acids and protein. Carbohydrate may be entirely absent, or substituted for a portion of the protein; this choice has important metabolic effects. The VLCD products are usually a powder which is mixed with water or another low-food-energy liquid. The VLCD is prescribed on a case to case basis for rapid weight loss (about 1.5 to 2.5 kilograms or 3 to 5 pounds per week) in patients with Body Mass Index of 30 and above. The health care provider can recommend the diet to a patient with a BMI between 27 and 30 if the medical complications the patient has due to being overweight present serious health risks.
A 1997 study concludes that the short-term use of a VLCD is very effective in rapidly improving glycaemic control and promoting substantial weight loss in obese patients with Type 2 diabetes. Moreover, a VLCD increases insulin sensitivity and reduces the substrate for gluconeogenesis. Thus VLCD treatment may improve glycaemic control more than calorie restriction alone. A VLCD is typically undertaken by an obese patient who wishes to lose a lot of weight quickly, as the risk to health that obesity presents is considered much greater than any risks of the diet itself, so long as it is undertaken with medical supervision.
Studies have shown that in about one in four individuals following a VLCD for a few months, gallstones develop. However, these gallstones may be small enough to not cause discomfort, and often disappear when a normal eating pattern is resumed. Gallstone formation is facilitated by the more concentrated bile fluid and reduced flow as a result of a VLCD. Another potential side effect is constipation (depending on the fiber content of the diet). Unmonitored VLCDs with insufficient macronutrient and mineral intake have the potential to cause sudden death via ventricular tachycardia. 
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- Diabetes for Professionals – VLCD in the treatment of obese patients with Type 2 diabetes: does it make sense?
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- Nutra-Smart – VLCD's & Meal Replacements - A critical look