The cabbage soup diet, the low-carbohydrate and high-protein diet, and other so-called "fad" diets are fundamentally different from federal nutrition dietary guidelines and are not recommended for losing weight.

Fad diets usually overemphasize one particular food or type of food, contradicting the guidelines for good nutrition, which recommend eating a variety of foods from the Food Guide Pyramid. These diets may work at first because they cut calories, but they rarely have a permanent effect.

A high-protein diet is one fad diet that has remained popular over the years. "High-protein items may also be high in fat," says Robert Eckel, M.D., professor of medicine at the University of Colorado Health Sciences Center in Denver. High-fat diets can raise blood cholesterol levels, which increases a person's risk for heart disease and certain cancers.

High-protein diets force the kidneys to try to get rid of the excess waste products of protein and fat, called ketones. A buildup of ketones in the blood (called ketosis) can cause the body to produce high levels of uric acid, which is a risk factor for gout (a painful swelling of the joints) and kidney stones. Ketosis can be especially risky for people with diabetes because it can speed the progression of diabetic renal disease, says Eckel.

"It's important for the public to understand that no scientific evidence supports the claim that high-protein diets enable people to maintain their initial weight loss," says Eckel. "In general, quick weight-loss diets don't work for most people."