Trade Carbs for Proteins: Heart Healthy?

Researchers Find Small Dietary Shifts Can Reap Heart and Blood Pressure Benefits

Medically Reviewed by Louise Chang, MD on November 15, 2005
From the WebMD Archives

Nov. 14, 2005 -- Trading in a slice of bread for a handful of nuts or drizzle of olive oil may help in the fight against high blood pressure and heart disease.

A new study suggests that swapping out a small amount of carbohydrates in an already heart-healthy diet for either protein-rich foods or unsaturated fats may provide additional benefits in lowering heart disease risk.

Researchers compared the effects on blood pressure and cholesterol levels of a healthy carbohydrate-rich diet -- based on the Dietary Approaches to Stop Hypertension (DASH) diet -- to similar diets with about 10% of the carbohydrates replaced with protein from mostly plant sources or unsaturated fats.

Reducing Heart Risk

"All three diets reduced overall heart disease risk, lowering blood pressure and improving cholesterol levels," says researcher Lawrence Appel, MD, MPH, professor of medicine at the Johns Hopkins School of Medicine, in a news release. "But the protein and monounsaturated fat diets had an edge over the carbohydrate-rich diet."

The protein-rich diet reduced heart disease risk by 21%, and the monounsaturated-fat-rich diet reduced it by almost 20%, compared with the 16% reduction found with the carbohydrate-rich diet.

"Our study provides strong evidence that replacing some carbohydrate with either protein or monounsaturated fat has important health benefits," says Appel. "There is already agreement that reducing saturated fat lowers risk for heart disease, but the question of which macronutrient [fat, protein, or carbohydrate] to emphasize has been controversial."

Trade in a Few Carbs for Heart Benefits

Researchers stress that none of the diets studied was low in carbohydrates or very high in protein. Instead, all three of the diets were low in saturated fat (the fat found in meat and dairy products), cholesterol, and sodium; the diets were rich in fruits, vegetables, fiber, potassium, and other minerals at the recommended levels.

In the high-protein diet, researchers replaced approximately 10% of the total daily calories from carbohydrates with protein. About 50% of the protein came from plant sources, such as beans, nuts, seeds, and some grains. The unsaturated fat diet was enriched with monounsaturated fats and included olive and canola oils, as well as some nuts and seeds.

In the study, which appears in The Journal of the American Medical Association, researchers compared the effects of the three diets in 164 adults who either had high blood pressure or were on the verge of having it. All of the participants followed each diet with all the necessary foods provided to them for six weeks, with two to three weeks between each different diet. Food was prepared in research kitchens.

Blood Pressure and Cholesterol Changes

Researchers found that blood pressure and cholesterol levels improved after each diet phase compared with the start of the study. But the benefits achieved with the protein-rich and monounsaturated-fat-rich diets were greater than with the DASH-based diet alone.

In an editorial that accompanies the study, Myron H. Weinberger, MD, of Indiana University Medical Center, says the results of this study may be difficult to apply to the public.

He says the people in this study were highly motivated to follow the diets because of their blood pressure status and the fact that all of the foods were provided to them.

"Although the benefit of blood pressure reduction in those in the prehypertensive group is clear," Weinberger says the ability to control high blood pressure adequately in the people with existing hypertension is not clear. "It is likely that more than diet will be required to reach goal blood pressures for the majority of these individuals."

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SOURCES: Appel, L. The Journal of the American Medical Association, Nov. 16, 2005; vol 294: pp 2455-2464. News release, Johns Hopkins Medical Institutions.

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