By: Thomas Pickering, MD, DPhil, FRCP, Director of Integrative and Behavioral Cardiology Program
of the Cardiovascular Institute at Mount Sinai School of Medicine, New York.

The conventional recommendations for controlling blood pressure by dietary means are to restrict salt and lose weight. Vegetarians also have low blood pressure, and switching to a vegetarian diet has been shown to lower blood pressure. Other interventions, such as potassium and magnesium supplementation, have given inconsistent results. A new study has investigated the effects of diets rich in fruits and vegetables and low in fat, which has shown a very substantial effect on blood pressure.

The subjects were 459 people with borderline blood pressures (systolic below 160 mm Hg and diastolic between 80 and 95), who were fed a typical American diet for one month, and then randomly allocated to one of three dietary groups. The first group continued with the American diet. This was relatively high in saturated fat, red meat (one to two servings a day), snacks and sweets (four servings a day), and relatively low in fiber, fruits, and vegetables (about four servings a day). The second group received a 'fruits and vegetables' diet, in which the snacks and sweets of the American diet were largely replaced by fruits and vegetables (eight to 10 servings a day). The fat content was the same, however, and much of the fat came from butter. The third group received an 'ideal' diet, which was also rich in fruits and vegetables, but low in fat. The composition of the diets are shown in the Table 1, and the types of food which were consumed in Table 2.

Table 1: Nutrient Content of the Ideal DASH diet and a typical American diet

Table 2: Composition of Ideal DASH diet compared to average American diet

The study was conducted at several centers throughout the United States, and subjects ate at least one meal per day at the center. They were then given a cooler containing the other two meals for the next 24 hours. At the end of eight weeks, the subjects eating the Fruit & Vegetable diet had lowered their blood pressure by 2.8/1.1 mm Hg (systolic/diastolic) more than the group eating the American diet. The corresponding reduction in the group eating the Ideal diet was 5.5/3.0 mm Hg. One hundred and thirty three of the subjects were hypertensive at the beginning of the study (blood pressures higher than 140/90 mm Hg), and in them the fall of blood pressure was even more marked - 11.4/5.5 mm Hg. The falls in blood pressure occurred within two weeks and were maintained for the remaining six weeks of the study.

Doctor’s Comments

The reductions of blood pressure shown in this study in people who ate the Ideal diet are of impressive magnitude and bigger than in many other dietary intervention studies. One reason for this may have been that it was a 'feeding' study rather than a 'counseling' study — the subjects were provided with all their meals. The diet resembled the 'Mediterranean' diet that is gaining a lot of support as the 'ideal’ diet for general health, not just blood pressure, although it was lower in fat. One of the interesting lessons from this study is that you don’t have to reduce your salt intake to lower your blood pressure. The three diets all had the same amount of salt, which was actually more than the 2,240 mg recommended on food labels.

Where it was published