September 27, 2010

Blood pressure–lowering diet may also reduce risk of heart disease

A new study suggests yet another reason for Americans to abandon their current fatty diets in favor of one rich in fruits and vegetables and low in saturated fat. Choosing these healthier options appears to significantly reduce the long-term risk of heart disease in patients with mildly elevated blood pressure, particularly African-Americans.

Long known to reduce blood pressure and now recommended in national guidelines, this healthier diet—known as the DASH diet for Dietary Approaches to Stop Hypertension—also reduces heart disease risk, even in people who do not lose weight, according to a Johns Hopkins study published online Aug. 31 in the journal Circulation: Cardiovascular Quality and Outcomes.

“One of the most noteworthy findings is the remarkable reduction in heart disease risk among African-Americans,” said Nisa M. Maruthur, an assistant professor of medicine in the Division of General Internal Medicine at the Johns Hopkins University School of Medicine and one of the study’s authors. “African-Americans in the United States tend to have worse outcomes than whites from cardiovascular disease, and here is one way they may be able to help prevent it.”

The DASH eating plan emphasizes fruits, vegetables and low-fat dairy products; includes whole grains, poultry, fish and nuts; and is reduced in fats, red meat, sweets and sugar-containing beverages.

Maruthur’s research shows that subjects who ate the DASH diet likely decreased their 10-year risk of coronary heart disease by 18 percent over those who ate a more typical American diet, and by 11 percent over those who ate a diet rich in fruits and vegetables but otherwise similar to a typical American diet.

In African-American subjects, the decrease in 10-year risk of coronary heart disease was even more pronounced: Those on the DASH diet saw their risk decline by 22 percent over those on a typical diet, compared to 8 percent for white subjects.

Compared to the typical American diet, the DASH diet (with its nine to 11 servings of fruits and vegetables a day) lowered blood pressure, total cholesterol and LDL cholesterol as well as HDL cholesterol. It had no effect on levels of triglycerides, fatty acids also linked to heart disease.

The research was done using data from the DASH trial of the 1990s, in which 459 people with elevated blood pressure not high enough to require medication were sorted into three groups. For eight weeks, each group ate one of three diets: the DASH diet, a diet rich in fruits and vegetables but otherwise comparable to a typical diet, or a more typical fatty American diet. All the food was provided by researchers, who carefully measured portions and determined the nutrient content of the meals being served. Using a risk assessment calculator devised by the Framingham Heart Study, Maruthur’s team was able to estimate heart disease risk.

Maruthur said that the reason that the diet likely reduces coronary heart disease risk is that it reduces both blood pressure and blood cholesterol levels, two independent risk factors for coronary disease.

One drawback of the study—and of almost any study of lifestyle interventions—is that it relies on estimates for determining heart disease risks in the long term. Researchers point out that it would take too much time and money to follow people for the decades required to see if the prescribed diet helps reduce actual heart attacks and heart disease deaths.

For years, doctors and policymakers have talked about the detrimental effects of the typical American diet on the nation’s health. Physician, advocacy and government groups have advocated for widespread adoption of a diet similar to the DASH diet. But the message, Maruthur said, still hasn’t gotten through.

“It’s no secret that we should be eating less saturated fat and more fruits and vegetables,” she said. “But how do we get the general population to adopt the DASH diet? The public health benefits could be enormous.”

Lawrence J. Appel and Steven T. Chen co-authored the study.