DASH Diet of Fruits, Vegetables, Low Fats Reduces Blood Pressure
August 1, 1999 7 minutes read
DASH Diet of Fruits, Vegetables, Low Fats Reduces Blood Pressure
By Pat McGinley, FNP, MSN
Summary—Hypertension (HTN) is a common, serious, chronic illness that affects more than 50 million adults in the United States. Morbidity and mortality associated with HTN account for millions of health care dollars and office visits annually. Prevention of hypertension by improving lifestyles is key to reducing these numbers. Researchers compared the effects of three types of diets on blood pressure control in adults.
Results demonstrated that a diet rich in fruits and vegetables and limited in fats reduced blood pressure. This diet was especially effective in African-Americans, who are known to be at high risk for hypertension. The diet was well-accepted, easy to implement, and reasonable in cost, and it maintained the patient’s weight even without a reduction in sodium intake. Early dietary intervention is an effective preventive measure for hypertension.
Hypertension affects more than 50 million adults and is one of the leading causes of morbidity and mortality in the United States. Its associated morbidity includes stroke, retinopathy, renal dysfunction, heart failure, and coronary heart disease.1 As we enter the 21st century, hypertension continues to represent a major challenge for health care providers, government health agencies, and the population at large, not only in control and treatment but in prevention as well.
The Dietary Approaches to Stop Hypertension (DASH) clinical trials in 1997 demonstrated that a daily diet of 8-10 fruits and vegetables, 2-3 servings of low-fat dairy, and decreased saturated and total fats significantly reduced blood pressure.2 (See patient education handouts on the DASH diet and sensible use of salt, enclosed in this issue.)
A more recent multicenter study expanded on those results to determine what the dietary effects would show on three subgroups of patients. Results indicated the DASH combination diet significantly lowered blood pressure in all of the subgroups participating in the study but was most effective in African-Americans and hypertensive individuals.3
Study Design
The randomized controlled feeding study was conducted at four academic medical centers throughout the United States over an eight-week period. The purpose of the study was to compare the effects of three dietary intake patterns on blood pressure in people with stage 1 hypertension (140-159/90-99) and those with high normal blood pressure. The three dietary patterns were:
Diet 1.
A control diet was typical of American intake patterns, with about 2100 calories composed of 37% fats; 15% protein with 2.5 servings meat, fish, or fowl; 300 mg cholesterol; 3000 mg sodium; 9 g fiber; 2-3 fruits/vegetables; and a half serving of low-fat or regular-fat dairy. (N= 154)
Diet 2.
Diet 2 was a fruit and vegetable diet consisting of intake high in fruits and vegetables but no limits on other nutrients, with about 2100 calories composed of 37% fat; 15% protein with 2.5 servings meat, fish, or fowl; 300 mg cholesterol; 3000 mg sodium; 31 g fiber; 5-8 fruits/vegetables; and a half serving regular-fat dairy. (N=154)
Diet 3.
Diet 3 is a combination diet consisting of 8-10 fruits and vegetables; low-fat dairy foods; only modest intake of protein, low saturated fats, total fats, and cholesterol, with about 2100 calories composed of 27% fat; 18% protein with 1.6 servings meat, fish, or fowl; 150 mg cholesterol; 3,000 mg sodium; 31 g fiber, nine fruits/vegetables; two servings of low-fat dairy; and a half serving regular-fat dairy. (N=151)
The study cohort was obtained through mass mailings, public service announcements, and advertisements. Participants were paid $150-$600 for completion of the study. The study was designed to include two-thirds minority participants, especially African Americans because they are at higher risk for hypertension as well as increased morbidity.
Participation criteria for the study included:
• subjects ages 22 or older;
• and average untreated blood pressure taken in sitting position on three screening visits of < 160/80-95 mm/Hg.
Exclusion criteria included:
• presence of diabetes, hyperlipidemia, coronary heart disease, renal insufficiency, pregnancy, or other chronic medical problems that would interfere with participation;
• body mass index (BMI) > 35 (weight in kilograms divided by the square of height in meters);
• use of medications that affect blood pressure;
• alcoholic beverage intake of > 14 drinks per week;
• and unwillingness to discontinue use of antacids or vitamin and mineral supplements that contain magnesium or calcium.
The study cohort consisted of 459 participants:
• 60% African-American;
• 34% non-Hispanic white;
• and 6% other minorities.
Women constituted 49% of the subjects, of whom 33% were white and 59% African-American. More than half of the study participants were classified as obese, with women and African-Americans having higher rates of obesity than men and whites. The mean physical activity level was classified as sedentary.
Pre-participation diet analyses revealed daily fat intake was 39% in African-Americans and 38% in whites. African-Americans consumed 5.4 servings of fruits/vegetables while whites consumed 6.1 servings. Trained staff measured two blood pressures using random-zero sphygmomanometers after the subject rested quietly for five minutes in a sitting position.
The average of three screening and four initial phase pairs of blood pressure measurements defined baseline blood pressures. The average of four or five pairs of blood pressure measurements defined follow-up blood pressures, which were taken during the last 1-2 weeks of the intervention phase.
Study Methodology
The study was conducted in two parts. During the initial (run-in) phase, participants ate a controlled diet over a three-week period. If they successfully adhered to the diet during this period, they were randomized into one of the three treatment diet categories. Once randomized, participants were fed at each of the four clinical centers over an eight-week period (the intervention phase).
One meal a day (either lunch or dinner) was consumed at a clinical center. The remaining meals were distributed as a "takeout" to be consumed off site for the rest of the 24-hour period. Weekend meals were given out on Fridays and consumed off site. Caffeinated beverages were limited to < 3 per day. Alcoholic beverages were limited to < 30 g per day. Participants were instructed to eat all and only the study foods. Each person kept a daily diary of any nonstudy foods consumed as well any required study foods that were not eaten.
Study Results
Researchers initially analyzed the data according to the diet followed throughout the study. Further analysis measured:
• differences among the races;
• hypertension status;
• sex;
• BMI;
• education;
• annual income;
• physical activity level;
• alcohol intake;
• and family history.
The study was completed by 446 subjects. The most significant results were that the combination diet lowered blood pressure in all subgroups. This diet was particularly effective in decreasing blood pressures in African- Americans and those with hypertension. Only those with little education or those who consumed alcohol saw no change in blood pressure. The DASH combination diet was successful in lowering systolic and diastolic blood pressure. The DASH diet reduced blood pressure in African-Americans with hypertension by 13.2/6.1 mm/Hg. Among normotensive African-Americans on the DASH diet, blood pressure was reduced by 4.3/2.6 mm/Hg. Among hypertensive whites, the DASH diet reduced blood pressure by 6.3/4.4 mm/Hg and 2/1.2 mm/Hg in normotensive subjects. The combination diet also resulted in reduction of blood pressure that was less than that which resulted from the DASH diet but greater than that from the control diet. The blood pressure reduction of 7.1/2.8 mm/Hg was significant only in the subjects who had existing hypertension.
Clinical Implications
This study has tremendous potential not only for treating patients with existing hypertension but for normotensive individuals who are at risk for developing hypertension. The study results indicate that early dietary intervention using the DASH diet can prevent or delay the onset of hypertension. For hypertensive patients, initiation of diet therapy is a vital component of the medical management plan and may be successful enough to delay initiation of drug therapy. When the patient history reveals risk factors for hypertension in a normotensive patient, education should begin at once.
Current national guidelines for hypertension management recommend reduced sodium intake, weight reduction in the overweight, and moderation of alcohol intake.4 Patients with high-normal blood pressure need to know they are at increased risk of blood pressure-related morbidity and mortality even though they do not have clinical hypertension.
The DASH diet is healthful, reasonably priced, low-risk, easy to implement, and consistent with current recommendations for reduction of heart disease, cancer, and osteoporosis. The DASH combination diet lowered blood pressure without reducing weight and sodium intake. A study to determine the effect of reducing sodium intake in combination with the DASH diet is under way. The combination of all three — the DASH diet, weight reduction, and sodium reduction — should be the first step in hypertension control. Clinicians who practice early intervention for their patients, especially among African Americans, can reduce morbidity and mortality associated with hypertension.
References
1. The sixth report of the Joint National Committee on Prevention, Detection, Evaluation, and Treatment of High Blood Pressure. Arch Int Med 1997;157:2413-2446.
2. Appel LJ, Moore TJ, Obarzanek E, et al. A clinical trial of the effects of dietary patterns on blood pressure. N Engl J Med 1997;336:1117-1124.
3. Svetkey L, Simons-Morton D, Vollmer W, et al. Effects of dietary patterns on blood pressure. Subgroup analysis of the Dietary Approaches to Stop Hypertension (DASH) randomized clinical trial. Arch Int Med 1999;159:285-293.
4. National High Blood Pressure Education Program. Working Group Report on Primary Prevention of Hypertension. NIH Publication 93-2669. Washington, DC: National Heart, Lung, and Blood Institute; 1993.
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