Background of the Science behind the DASH Dietary Recommendations made in the video of this website.  (DASH- Dietary Approaches to Stop Hypertension)       back

There have been multiple early studies and observations suggesting that a low salt diet as well as a vegetarian diet have favorable effects on high blood pressure ^{1, 2}.

The National Institute of Health (NIH) subsequently supported two landmark trials which showed the effect of DASH dietary modifications  and then the addition of a low sodium diet which were published in 1997 and 2001 ^3,4. The benefits of the DASH diet were established and the details of this diet have been described extensively, including on the NIH website.⁵

In 2005, a number of the authors of the initial DASH diet trials were part of a study⁶ that aimed to improve upon the DASH diet. The initial DASH diet was compared to two different diets that were similar to the DASH diet, but had distinct differences as well. These two dietary modifications both led to improved results. Blood pressures on the modified diets were lower and cholesterol profiles tended to be improved with both diets which in a sense represented modifications of the DASH diet.

The three diets that were compared were:

1. Standard DASH diet. (Though with slightly less protein- 15% vs. 18%)

2. A diet with less carbohydrate than the standard DASH diet and predominantly more monounsaturated fat with sources that included olive oil, canola oil, nuts and seeds. (Carbohydrate intake was decreased but continued to represent 48% of the diet.)

3. A diet with more protein than the standard DASH diet (2/3 of the additional protein was vegetable protein). Carbohydrate was similarly decreased but still represented 48% of the calories of this diet.

All three of these diets were tested in a setting where all the food and meal preparation was performed for the patients so the diets could be very precisely controlled.

Since both the modified diets were better than the standard DASH diet for blood pressure control and lipid levels, they appear to have some preferable features.

The DASH diet that is presented with the video and the handout represents an attempt to present some of the common elements present in the DASH diet. There is some degree of difference compared to the initial DASH diet which in part reflects the findings of the 2005 trial ⁶.   Daily intake of nuts, seeds, and legumes averaged 0.7 servings daily in the original DASH diet³, whereas 1-2 servings is recommended in the video because subsequent information has suggested an increase in plant based protein is beneficial.⁶ Furthermore, monounsaturated oils were emphasized over other oils consistent with the subsequent trial⁶.  In addition, a bias by the author towards whole grain carbohydrates has been introduced in the video which is not required by the DASH diet

The DASH diet has been simplified on this video. When instructed by a dietician a patient’s daily caloric needs are estimated and the amount of food is then adjusted accordingly. For example, a person that requires 1500 calories a day is instructed with the DASH diet³ to eat 4 vegetables servings and 4 fruit servings.  A person requiring 2500 calories is advised to eat 5 vegetable and 5 fruit servings. The video simply recommends a generic 4-5 vegetable serving and 4 fruit servings in order to simplify the instruction.  

In regards to the simplifications made, this was the result of my experience of instructing patients in the office. Unlike the participants in the studies who had their food prepared for them, the patient receiving information in a single session needs clear straight forward instructions. Though a dietician has more time for fine tuning, in my office, the more straight forward the presentation, the higher the success rate the patients reported in following the DASH diet.

Finally, details on the dietary changes that improved blood pressure and lipid levels compared to the standard DASH diet are given below to increase understanding of the three diets⁵ described in the JAMA 2005 article.

The JAMA study⁵ included example meal plans to help more fully describe the diets.
The following chart uses the data presented in the JAMA study⁵ to show the type, as well as the details, of the diets that were tested in that study.

* Though all the diets contained olive oil there was significantly more olive oil in the Unsaturated Fat diet
 

1.  Dole V, Dahl L, Cotzias G, Eder H, Krebs M. Dietary treatment of hypertension; clinical and metabolic studies of patients on the rice-fruit diet. J Clin Invest 1950; 29(9): 1189-206
2.  Sacks FM, Kass EH. Low blood pressure in vegetarians; effects of specific foods and nutrients. Am J Clin Nurt. 1988; 48: 795-800.
3. 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.
4. Sacks FM, Svetkey LP, Vollmer WM, et al. Effects on blood pressure of reduced dietary sodium and the dietary approaches to stop hypertension (DASH) diet. N Engl J Med. 2001;344:3-10.
5. The specific recommendations for the initial DASH diet are available for download from the NIH website:  http://www.nhlbi.nih.gov/health/public/heart/hbp/dash/
6. Appel LJ, Sacks FM, Carey VJ, et al; OmniHeart Collaborative Research Group.

Effects of protein, monounsaturated fat, and carbohydrate intake on blood pressure and serum lipids: results of the OmniHeart randomized trial.

JAMA. 2005 Nov 16;294:2455-64.

Nutrition