Very low-calorie diet for obesity

A very low-calorie diet (VLCD) may be considered if you are obese and need to lose weight quickly to protect your health and if your health professional decides it is safe for you. VLCDs generally are not recommended. A VLCD is also known as a rapid weight-loss diet.

VLCDs supply from 250 to 800 calories per day. Do not start one of these diets without the help of a health professional. Diets this low in calories do not provide enough vitamins and minerals for good health unless the diet is specially prepared. A diet that does not have enough vitamins or minerals can lead to serious, potentially fatal health problems.

These diets are not recommended if you have heart problems, blood clotting problems, bleeding ulcers, liver disease, kidney disease, or cancer or if you have had a stroke. If you are older than 50, you will need frequent monitoring by your health professional to be sure you are losing fat and not muscle.

However, research reports that although initial weight loss is greater on a VLCD than on a low-calorie diet, in the long term about the same amount of weight is lost in both types of diets.¹

People on these diets often feel tired or have constipation, nausea, or diarrhea as a side effect. However, for most people, this goes away in a few weeks.

The most common serious side effect is developing gallstones. People who are obese are more likely to develop gallstones than people who are lean, and when a person who is obese uses a very low-calorie diet, the chance that he or she will develop gallstones becomes even greater. People who lose a large amount of weight quickly are at greater risk than those who lose weight more slowly. Studies have shown that people who lose more than 3lb per week are at greater risk for developing gallstones.² However, you can take medicine that helps prevent gallstones from forming.

Following are the changes your body goes through during a VLCD:

• Your metabolism slows to conserve energy because the body thinks it is starving.
• To get the carbohydrate it needs, your body breaks down protein. This causes a loss of lean body mass such as organ and muscle tissue. It is important to preserve lean tissue, because it increases your basal metabolic rate. Losing too much lean tissue increases the percentage of fat in your body. The result is a reduced metabolism. This is one reason why it is so easy to regain weight after you lose weight quickly.
• In a VLCD (or during starvation), about half the weight you lose is fat and the other half is lean tissue, such as muscle. On a more moderate diet, you lose 3 times more fat than lean tissue.
• Mineral and electrolyte imbalances can occur. These imbalances can be life-threatening. This is the reason these VLCDs must only be used under a health professional's supervision.
• Bone mass is lost. This is more risky for women, because they diet more often than men, and they are also at higher risk for developing osteoporosis.

Citations

1. American Gastroenterological Association (2002). AGA technical review on obesity. Gastroenterology, 123(3): 882–932. [Erratum in Gastroenterology, 123(5): 1752.

2. National Institute of Diabetes and Digestive and Kidney Diseases (2006). Dieting and Gallstones (NIH Publication No. 02–3677). Available online: http://www.win.niddk.nih.gov/publications/gallstones.htm#whatare.