The advisory specifically targets such popular "quick weight loss" regimens as the Atkins, Zone, Protein Power, Sugar Busters and Stillman diets, and offers guidelines to health care professionals for evaluating these 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," says Robert H. Eckel, M.D., immediate past chair of the Association's Nutrition Committee and a 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."
One of the most compelling arguments against following a high-protein diet, Eckel says, is that these diets have not been documented to deliver on their promise of sustained, long-term weight loss. The safety, credibility and effectiveness of the revised American Heart Association nutritional guidelines, on the other hand, are backed by scientific documentation, he adds.
"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," he says. "In general, quick weight-loss diets don't work for most people."
Studies have consistently shown 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, says Eckel, a professor of medicine at the University of Colorado Health Science Center in Denver.
Foods emphasized in some of these high-protein and similar diets are from animal sources that are rich in both 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 says.
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 adds.
The statement notes that 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.
"This 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 says. "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. Limitation of 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 emphasizes. "In some individuals with kidney or liver disease, unneeded protein may put them at risk of worsening their disease."
More than half of all adults in the U.S. are either overweight or obese. "Many of these people are looking to high-protein diets as a popular 'new' strategy for successful weight loss," says Eckel. "This dietary concept really isn't new at all. It's been around for decades in one form or another."
High-protein diets induce a quick drop in weight primarily through loss of body fluids caused by the diuretic effect of eliminating most carbohydrates, he explains. Glycogen, the form of sugar used by the body for energy, is lost from the muscles as well, sometimes causing fatigue. In general, some of these diets also induce ketosis, a metabolic condition associated with low blood levels of insulin and resulting when the body is deprived of dietary carbohydrates. Sustained ketosis also causes a loss of appetite, which may lead to lower total calorie intake.
"A very high-protein diet is especially risky for patients with diabetes because it can speed the progression ... of diabetic renal disease..." the statement adds. "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."
Also contributing to the advisory were Sachiko T. St. Jeor, R.D., Ph.D.; Barbara V. Howard, Ph.D.; T. Elaine Prewitt, R.D., Dr. P.H.; Vicki Bovee, R.D., M.S.; and Terry Bazzarre, Ph.D.
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