August 21, 2000
--DASH diet also lowers blood pressureResearchers at Johns Hopkins have found yet another reason to eat a well-balanced diet low in fats and rich in fruits and vegetables: It lowers blood levels of homocysteine, thereby reducing the risk of heart disease.
Homocysteine, an amino acid, is a by-product of protein metabolism. Epidemiological studies have shown that too much homocysteine in the blood is related to an increased risk of heart disease and stroke. Homocysteine can injure the cells that line arteries and stimulate growth of smooth muscle cells, narrowing the channel for blood flow. It also can disrupt normal blood-clotting mechanisms, increasing the risk of clots that can lead to heart attack or stroke.
In a three-month study of healthy adults, a well-balanced diet, also termed the Dietary Approaches to Stop Hypertension (DASH) diet, significantly lowered homocysteine in comparison to a typical American diet. Researchers say the change in homocysteine is predicted to reduce the risk of heart disease by 7 to 9 percent, and reductions in blood pressure and cholesterol from the DASH diet should reduce the risk of heart disease even further.
"Our work shows that modifying the diet can have multiple benefits, beyond changes in traditional risk factors such as blood pressure and cholesterol," says Lawrence J. Appel, M.D., M.P.H., lead author of the study and an associate professor of medicine at Johns Hopkins. "To get these benefits, people should eat a well-balanced diet. It's not enough to eat just an occasional fruit or vegetable while consuming a high-fat diet."
Study results are published in the August 22 issue of Circulation, an American Heart Association journal. This study was part of the original DASH trial, which showed that the DASH diet significantly lowered blood pressure. Results were published in 1997. The DASH diet emphasizes fruits, vegetables and low-fat dairy products. It includes whole grains, poultry, fish and nuts; it is reduced in fat, red meat, sweets and sugar-containing beverages.
For the first three weeks, all study participants were fed a typical American diet low in fruits, vegetables and dairy products and relatively high in fat. For the next eight weeks, participants followed one of three randomly assigned food plans: a continuation of the typical American diet; a diet rich in fruits and vegetables but otherwise similar to the first; or the DASH diet. Participants were provided all of their food. Each weekday, participants ate either lunch or dinner at ProHealth, a Hopkins-affiliated clinical center in Woodlawn, Md. After completing the on-site meal, they received coolers that contained other meals to be eaten off-site.
Unlike the DASH diet, which lowered homocysteine by 0.34 micromoles per liter, the typical American diet raised homocysteine by 0.46 micromoles per liter. The fruits and vegetables diet had an intermediate effect. The more folate in the diet, the lower the homocysteine. Folate is a B vitamin that helps to break down homocysteine in the body.
Study participants tended to be middle-aged. Approximately half were women and two-thirds were minorities, primarily African-American.
The study was supported by the National Heart, Lung and Blood Institute and the U.S. Department of Agriculture.
Other authors were Edgar R. Miller III, M.D., Ph.D.; and Thomas Erlinger, M.D., of Hopkins; Sun Ha Jee, Ph.D., of Yonsei University, Seoul, Korea; Rachael Stolzenberg-Solomon, Ph.D., M.P.H., R.D., of the National Cancer Institute; Pao-Hwa Lin, Ph.D., of Duke University Medical Center, Durham, N.C.; and Marie R. Nadeau and Jacob Selhub, Ph.D., of Tufts University, Boston.
Johns Hopkins' Welch Center for Prevention, Epidemiology and Clinical Research
DASH Trial (and further information about the diet)
American Heart Association
National Heart, Lung and Blood Institute