Hypertension is an important public health issue and contributes to the incidence of stroke and coronary heart disease. The prevalence of hypertension in Australia was recently shown to be approximately 29%. Furthermore, hypertension accounts for 6.1% of the total problems managed in general practice. The prevalence of obesity in Australia has more than doubled in the past 20 years, and almost 60% of adults have been estimated to be overweight or obese. There is a direct positive relation between overweight and hypertension, such that it has been estimated that the control of obesity may eliminate 48% of the hypertension in whites. Dietary sodium increases blood pressure (BP), whereas dietary potassium lowers the risk of hypertension and stroke. In a controlled intervention study, a multifaceted dietary approach--Dietary Approaches to Stop Hypertension (DASH) that included a diet high in fruit, vegetables, and low-fat dairy products was shown to result in large decreases in BP. Therefore, the aim of the present study was to determine the effect on BP of a DASH-type weight loss diet (WELL diet) and to compare this with usual low-fat dietary advice (LF diet) in free-living individuals who selected and prepared their own food.

Ninety-four men attended one screening appointment, and 63 who met the entry criteria and wished to participate undertook baseline home BP measurements for 2 weeks and were then randomly assigned to either the LF or the WELL diet. Subjects were seen twice at baseline, and commenced a 12-week intervention study and were seen at weeks 2, 4, 8, and 12. Phone contact was made with the subjects at weeks 6 and 10. Clinical BP, height, and weight were measured at baseline. Subjects monitored their home BP daily for 2 weeks before being randomly assigned to 1 of the 2 diets.

Subjects completed a 24-h dietary record each fortnight on the day before their visit with study staff. A food-frequency questionnaire was completed at baseline and at week 12 to assess usual intake of fruit, vegetables, and dairy products. Subjects were assisted with setting goals for exercise and diet. Dietary counseling was overseen by the coordinating dietitian and was provided by trained research staff The WELL diet was based on the DASH diet. This diet included advice to consume >4 servings of fruit or fruit juice [1 serving = 1 medium piece of fruit or fruit juice, >4 servings of vegetables [1 serving = 0.5 cup cooked vegetables, 1 cup salad vegetables, or 1 medium potato] and >3 servings of nonfat dairy products [1 serving = milk, yogurt, or cottage or ricotta cheese (0.5 cup)] per day. Fish was to be consumed >3 times per week, legumes (1 serving = 1 cup cooked) at least once per week, and unsalted nuts and seeds 4 times per week. Red meat was restricted to no more than 2 servings per week and fat to a maximum of 4 servings (4 teaspoons) per day. Subjects were advised to avoid butter, added salt (table or cooking), and obviously salty foods and to use lower-salt (<380 mg Na per 100 g) monounsaturated or polyunsaturated margarine. Those in the WELL group received a detailed dietary information booklet, recipes, and simple advice (tips).

The LF group was advised to limit their intake of high-energy foods and drinks, reduce their saturated fat intake, choose mainly plant-based foods, consume nonfat or reduced-fat milk and yogurt, limit their cheese and ice cream intake to twice per week, select lean meat, and avoid frying foods in fat. No specific targets were set. The 'Healthy Weight Guide' booklet by the National Heart Foundation of Australia (2002) was provided, together with the same recipes and tips as received by the WELL group. A maximum of 4 caffeine-containing drinks per day (for example, cola drinks, coffee, and tea) and 4 standard (10 g alcohol) alcoholic drinks per week were permitted for both diet groups.

The main difference between the LF diet and the WELL diet was that the WELL diet had specified targets for fruit, vegetable, and dairy intake, whereas the LF diet provided general guidelines focusing on increasing fruit and vegetable intake and reducing fat intake, particularly saturated fat. All subjects were required to participate in moderate-intensity exercise for >30 min on all or most days of the week.

Nine subjects dropped out before completing the study (4 in the LF group and 5 in the WELL group); the subjects who dropped out did not differ significantly from the rest of the group with respect to age or body mass index (BMI). Eight found it too difficult to comply with the study demands, and one moved interstate. Of the 54 men who completed the stud), 18 were taking anti-hypertensive medications (9 WELL, 9 LF).

The amount of time spent walking increased in both groups over the intervention period, with no significant difference between the groups. At week 12, the WELL group reported a higher intake of dairy products, but there was no significant difference between the groups in fruit and vegetable intakes. Fruit intake increased significantly during the diet compared with baseline for both groups. For the WELL group only, intakes of dairy products and vegetables were significantly higher during the diet than at baseline. After adjustment for baseline dietary intake, the 24-h dietary records indicated that the reductions in dietary fat (g/d), saturated fat (g/d), percent of energy from fat, percent of energy from saturated fat, and sodium (mg/d) were greater in the WELL group than in the LF group, and the increases in the percent of energy from protein, percent of energy from carbohydrate, potassium (mg/d), calcium (mg/d), magnesium (mg/d), and phosphorus (mg/d) were greater in the WELL group than in the LF group.

Weight decreased significantly in both groups by approximately 5 kg, with subjects in the WELL, group losing 6% of body weight and those in the LF group losing 5%. The rate of weight loss was not significantly different between the diet groups throughout the study. The greatest decrease in BP in both groups was seen after 4 weeks of intervention. There was a greater decrease in the WELL group than in the LF group in both systolic blood pressure (SBP) and diastolic blood pressure (DBP). Pulse rate also fell by 3.8 [+ or -] 1.6 beats/min more in the WELL group. The percentage decrease in SBP was 5.5 [+ or -] 1.0% in the WELL group compared with 1.4 [+ or -] 0.9% in the LF group. The percentage decrease in DBP was 6.4 [+ or -] 1.1% in the WELL group, compared with 1.0 [+ or -] 1.0% in the LF group.

The present study investigated the effects on home BP of 2 dietary interventions--one based on the DASH dietary pattern, and the other--a usual low-fat diet combined with increased physical activity to achieve weight loss. The subjects in both diet groups achieved a weight loss of approximately 5% to 6% of body weight over 3 months. Those in the WELL group, however, had greater decreases in SBP and DBP of approximately 5 mm Hg and 4 mm Hg, respectively. The groups were well matched at baseline for BP and for the number of subjects taking antihypertensive medication (33% in each group), although BMI was initially one unit higher in the LF group than in the WELL group. This difference, however, is unlikely to have contributed to the increased effectiveness of the WELL diet with respect to BP, because there was no significant difference in percentage weight loss between the groups.

The reason for the greater decrease in BP with the WELL diet is not clear. There was no significant difference between the two groups in the change in blood lipids, although those in the WELL diet group did appear to have a greater reduction in total fat, and particularly in saturated fat intake.

Some of the dietary differences between the WELL and the LF diet may explain some of the improved BP-lowering effect of the WELL diet, specifically, the increase in dietary potassium, which has been shown to lower BP by approximately 3 mm Hg systolic and 2 mm Hg diastolic. Dietary calcium and magnesium have also been weakly associated with lower BP in population studies, although evidence for a BP-lowering effect in controlled intervention studies is not consistent. It appears, however, that a diet combining these nutrient changes--for example, lower sodium, saturated fat, higher potassium, calcium, magnesium, and phosphorus--within a diet, and a physical activity pattern that induces negative energy balance, achieves a greater reduction in BP than a low-fat diet.