Thinking of trying one of the "new" high-protein diets to shave off some pounds? You better think again, national health experts are saying.

High-protein diets have no proven effectiveness in long-term weight reduction and pose potential health threats for those who adhere to them for more than a short time, according to a new advisory from the American Heart Association's nutrition committee.

The advisory, which appeared in the Oct. 9, 2001, issue of "Circulation: Journal of the American Heart Association," specifically targets some of the popular "quick weight loss" regimens, many of which have become best-selling books. It also offers guidelines to healthcare professionals for evaluating such diets.

"High-protein items may also be high in fat. Some of the diets increase fat intake and reduce nutritionally rich foods such as fruits and vegetables, which is not a good approach to meeting a person's long-term dietary needs," said Dr. Robert H. Eckel, immediate past chair of the AHA's nutrition committee and co-author of the advisory. "Many of these diets fail to provide essential vitamins, minerals, fiber and other nutritional elements, in addition to their high fat content."

Eckel also said high-protein diets have not been documented to deliver sustained, long-term weight loss, adding, "In general, quick weight-loss diets don't work for most people."

Studies have shown consistently that successful maintenance of weight loss occurs most often when people follow a nutritionally sound diet and increase physical activity to burn more calories than they consume, stressed Eckel, a professor of medicine at the University of Colorado Health Science Center, Denver.

Increasing Risk

Foods emphasized in some high-protein and similar diets are from animal sources that are rich in protein and saturated fat, such as meat and eggs. Meanwhile, some of the diets drastically limit consumption of high-carbohydrate foods such as cereals, grains, fruits, vegetables and low-fat milk products, Eckel said.

Eating large amounts of high-fat animal foods over a sustained period has been shown to increase the risk of coronary heart disease, diabetes, stroke and several types of cancer, he added.

According to the AHA statement, a diet rich in animal protein, saturated fat and cholesterol raises LDL cholesterol levels -- an effect that is compounded when high-carbohydrate, high-fiber plant foods that help lower cholesterol are limited or eliminated.

"That is why the American Heart Association urges most adults to limit fat intake to no more than 30 percent of total daily calories, less than 10 percent of which should be saturated fat," Eckel said. "On some of the high-protein diets, meeting these goals is simply impossible."

A diet high in complex carbohydrates that includes fruits, vegetables, non-fat dairy products and whole grains has been shown to reduce blood pressure, the statement continues. Limiting these foods, which are rich in calcium, potassium and magnesium (nutrients associated with blood pressure reduction), may lessen the benefit of weight loss on blood pressure reduction.

Although proteins are essential nutrients required to maintain the body's structure and proper function, most Americans already eat more protein than their bodies need, and excess dietary protein can, in itself, also increase health risks, Eckel stressed: "In some individuals with kidney or liver disease, unneeded protein may put them at risk of worsening their disease."

What's at Work

High-protein diets induce a quick drop in weight primarily through loss of body fluids caused by the diuretic effect of eliminating most carbohydrates, Eckel explained. Glycogen, the form of sugar used by the body for energy, is lost from the muscles as well, sometimes causing fatigue, he said. In general, some of these diets also induce ketosis, a metabolic condition associated with low blood levels of insulin that results when the body is deprived of dietary carbohydrates. Sustained ketosis also causes a loss of appetite, which may lead to lower total calorie intake, he said.

"A very high-protein diet is especially risky for patients with diabetes, because it can speed the progression ... of diabetic renal disease," the statement added. "Some popular high-protein, low-carbohydrate diets limit carbohydrates to 10-20 grams per day, which is one-fifth of the minimum 100 grams per day that are necessary to prevent loss of lean muscle tissue."