Blood pressure over the course of the DASH Trial intervention phase. The combination diet resulted in lower blood pressure than the control diet or fruits-and-vegetable diets. Blood pressure reduction took place in 2 weeks and was sustained throughout the trial.
When the research for the DASH Trial was undertaken by the researchers, it was noted that 24% have United States adults had hypertension. Is also noted that the current-guidelines recommended weight control, reduced intake of sodium, reduce alcohol consumption, and possibly an increase dietary potassium intake as lifestyle modifications. It was known that vegetarian diets reduce blood pressure possibly due to intake of more potassium, magnesium, fiber, calcium or through reduced fat intake. Trials had studied the changes in blood pressure when intake of these above items, was changed individually, but blood pressure reduction was inconsistent. The discrepancy between the blood pressure effects of the vegetarian diet and the trials of individual nutrient modification set the stage for the DASH Trial. It was speculated that there was a limited benefit of single nutrient supplementation and that a more holistic vegetarian diet could reduce blood pressure due to the combination of a wide variety of nutrient changes. This trial set out to study the benefit of making this combination of changes.
This trial enrolled 459 adults at least 22 years of age who were not taking antihypertensives with SBP < 160mmHg and DBP of 80-85mmHg. The length of the trial was 11 weeks including a three week run-in period and an eight week intervention period. All participants were given a controlled diet as part of a run-in period which is similar to that of the typical Western diet for a length of three weeks. At that point, the participants were divided into three groups and given different diets for a length of three weeks. One group was given a typical Western diet (called the control diet). A second group was given a diet rich in fruits and vegetables. A third group was given a combination diet (later termed the DASH diet). This combination diet was a combination of a diet that was rich in fruits and vegetables as well as low-fat dairy products with reduced saturated and total fat. Importantly, the sodium intake of all 3 groups was this same at 3 grams of sodium intake per day. They attempted to keep weight the same during the trial, but weight changes were -0.1kg, -0.3kg, and -0.4kg in the control, fruits-and-vegetables, and combination diets, respectively.
The fruits-and-vegetables provided a potassium and magnesium consumption close to the 75th percentile of U.S. consumption. The combination diet did the same. A 7 day menu with 21 meals at for caloric levels (1600, 2100, 2600, and 3100 Calories) was developed for each diet. The food was prepared and research kitchens according to a common protocol. Each week day, the subjects ate lunch or dinner on-site. After that meal, they were given coolers that contained the to be eaten off-site. On Fridays, they were given weekend meals to be consumed at home. The subjects were told to not drink more than 3 caffeinated beverages per day, no more than 2 alcoholic beverages per day. There also given 2 packets of salt each containing 2000mg of sodium that could be used at their discretion. Their weight was monitored each weekday and was kept stable by adding 100 Calorie cookies or muffins as needed. The outcome measured in this study was blood pressure.
At baseline, the mean blood pressure was 131.3/84.7mmHg. Among all participants, the combination diet reduced blood pressure by 5.5/3.0mmHg as compared to the control diet. The fruits-and-vegetables diet reduced blood pressure by 2.8/1.1mmHg as compared to the control diet.
This study included 133 patients with hypertension defined as a SBP > 140mmHg and DBP >90, or both. Among the hypertensive patients, the combination diet reduced blood pressure by 11.4/5.5mmHg as compared to the controlled diet. The conclusion of the trial was at a diet rich in fruits, vegetables, and low-fat dairy foods with reduced saturated and total fat can substantially lower blood pressure, even similar to that of antihypertensive drug monotherapy.
One of the interesting things about this study was the fact that low-fat dairy products reduced blood pressure greater than the fruits-and-vegetables diet. In the book Hypertension: A Companion to Braunwald’s Heart Disease, it noted that there has been some speculation about the reason for the additional benefit the combination diet as compared to the fruits and vegetables diet. Apparently, compared with fruits and vegetables diet, the combination diet had more vegetables, more low-fat dairy products, and more fish, and was lower and red meat, sugar, and refined carbohydrates. I have not found a better explanation for this other than one was noted in this book.
Overall, this is a great study with applications to how we should be counseling our hypertension patients. Of course consideration would need to occur in those with more advanced CKD to avoid hyperkalemia or other metabolic abnormalities. As always, a growing summary of hypertension trials can be found here.
DASH Trial: Appel, L. J., Moore, T. J., Obarzanek, E., Vollmer, W. M., Svetkey, L. P., Sacks, F. M., ... & Lin, P. H. (1997). A clinical trial of the effects of dietary patterns on blood pressure. New England journal of medicine, 336(16), 1117-1124.
DASH Trial PMID: 9099655
Useful summaries of the DASH Trial: Wiki Journal Club