Dietary Approaches to Stop Hypertension (DASH)

Objectives:

The primary objective of DASH was to identify and test the effects on blood pressure of dietary patterns in adult men and women at high risk of developing hypertension and subsequent cardiovascular disease.

Background:

In addition to high salt intake, excess weight, and high levels of alcohol consumption, a large body of evidence, primarily observational, suggested that several other dietary factors, including the amount and type of dietary fat, cholesterol, protein, fiber, and minerals such as potassium, calcium, and magnesium, may affect blood pressure. In contrast, randomized trials on mineral supplements (calcium, magnesium, potassium), fiber supplements, dietary fats, and protein have tested the hypotheses generated by observational studies and for the most part have shown small or no effects. It was hypothesized that certain patterns of food consumption rather than individual nutrients may have accounted for the associations observed between nutrients and blood pressure. The DASH study aimed to identify and test dietary patterns that were likely to favorably influence blood pressure based on epidemiologic studies. Three dietary patterns were developed: (1) A diet typical of what many Americans consumed was used as a control diet. This diet approximated the average macronutrient intake of Americans and the 25th percentile of mineral intake (calcium, potassium, and magnesium); (2) A diet high in fruits and vegetables, which resembled the macronutrient profile of the control diet and differed primarily in mineral and fiber content; and (3) DASH combination diet, which was high in fruits and vegetables, like the fruits and vegetables dietary pattern, but also was altered in macronutrient and dietary cholesterol consumption. It was reduced in saturated fat, total fat, and cholesterol and moderately increased in protein. Sodium levels were maintained at levels slightly below average U.S. consumption across all three diets.

Design and Subjects:

Four clinical centers and a coordinating center participated in the trial. DASH was an outpatient feeding study, and study staff prepared all meals and snacks in research kitchens. A total of 459 participants, age 22 years and older, with diastolic blood pressure 80-95 mm Hg, systolic blood pressure <160 mm Hg, and body mass index 35 kg/m2 were randomly assigned to one of three dietary patterns (described above) for a period of 8 weeks after a 3-week run-in period on the control diet. About 60% of the participants were African-American, and 49% were women. Recruitment occurred during 1994-1996.

Conclusions:

The DASH combination diet reduced systolic and diastolic blood pressure by 5.5/3.0 mm Hg compared to the control diet; the fruits and vegetables diet reduced blood pressure by about half as much, by 2.8/1.1 mm Hg (N Engl J Med 1997;336:1117-1124). The DASH diet lowered blood pressure in virtually all subgroups defined by race, sex, age, body mass index, education, income, physical activity level, alcohol intake, and hypertension status, and was particularly effective in African Americans and those with hypertension (Arch Intern Med 1999;159:285-293; Hypertension 2001;38:155-158). The DASH diet offers an additional nutritional approach to preventing and treating high blood pressure.