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The science behind the DASH diet, an overview: Part Two

Part One | Part Two

a variety of healthy ingredients, including vegetables, fruit, legumes, and grains, displayed individually in small bowls

DASH and Other Conditions

Researchers in the UK reviewed the available published studies to see if some conclusions might be drawn on the effects of a DASH diet on other heart disease factors.5 For their meta-analysis the researchers gathered research articles that were randomized, controlled trials comparing a group following a DASH diet to a control group and measured risk factors including blood pressures, glucose scores, and cholesterol scores. The 20 articles included a total of over 1,900 men and women and the studies lasted from 2 to 24 weeks. 

After analyzing the pooled results, DASH diet did result in improved blood pressures, with stronger results seen for those participants with higher starting blood pressures or higher Body Mass Indices. The DASH diet also helped improve total and LDL cholesterol levels, but no effect was seen on HDL cholesterol, triglyceride levels, or glucose scores. The authors do note that "the lack of a significant association between changes in BP [blood pressure] and dietary Na [sodium] intake is unanticipated." 

Polycystic Ovarian Syndrome (PCOS) affects as many as 18% of women worldwide. The name itself describes a fairly common effect of the disorder: multiple cysts on the ovaries that are believed to represent failed ovulation, which is also reflected by the infrequent or completely absent menstruation and infertility that is a symptom of the syndrome. Women with PCOS usually have increased levels of androgens, symptoms of hirsutism or acne and some level of Metabolic Syndrome. This combination of disorders also leads to poor lipid panels as well as higher markers of oxidative stress, which is likely to contribute to PCOS sufferers' higher risk of breast, endometrial, and ovarian cancers.

In one study of 96 clinically overweight or obese women with PCOS between the ages of 18 and 40, researchers randomly assigned each participant to one of two diets for an 8-week trial: a low-glycemic-index diet or a DASH diet.6 Both diets were designed to provide 52% of calories from carbohydrates, 18% from protein, and 30% of calories from total fat, and were calibrated for each woman's caloric needs at levels designed to induce moderate weight loss.

After assessing the women's food diaries at the end of the 8 weeks, the researchers could see that the two groups ate essentially the same amounts of carbohydrates, protein, and fats, but those following the DASH diet consumed more whole grains (but fewer grains overall) and far less sugar, along with more vegetables, fruits, nuts, seeds, and legumes. Women on the DASH diet lost more weight (over twice as much, on average), and had lower triglycerides and insulin levels along with higher levels of antioxidant capacity and higher levels of glutathione. 

In another study of a moderate-sodium DASH-type diet researchers found that in addition to the health benefits of the eating plan on blood pressure and bone health, DASH diet had a positive effect on improving mood in postmenopausal women.7

Other Variations on DASH Diet

Our research and attitudes toward dietary fats has changed dramatically in the last few years. One hurdle with DASH diet is the fairly low amount of saturated fat in the diet: the goal is about 6% of total calories from saturated fats and about 27% of total calories from all fats. For a 2,100 calorie diet that's about 14 grams of saturated fat and 63 grams of total fat. Researchers in Northern California looked at the role of dietary fat in the context of a DASH diet.8

Sixty normal and clinically overweight men and women participated in a feeding study to find out. They were randomly assigned to one of three groups, and that group rotated through three different diets (designed to maintain their weight) in a random order, following each diet for three weeks then following their own usual diet for two weeks. The three diets were as follows:

A control diet of 47% of calories from carbohydrates, 14% from protein, 38% from fat (16% saturated fat), and 141 grams of total sugar.
A DASH diet of 55% of calories from carbohydrates, 17% from protein, 27% from fat (8% saturated fat), and 158 grams of total sugar
A High Fat DASH (HF-DASH) diet of 43% of calories from carbohydrates, 18% from protein, 40% from fat (14% from saturated fat), and 93 grams of total sugar.

After each dietary period the participants were weighed; their waist and hip circumferences measured; blood drawn for cholesterol, glucose, and insulin scores; and their blood pressures were taken. The authors found that both the DASH and the HF-DASH reduced participants' blood pressures, both systolic (the top number) and diastolic (the bottom number) about the same amount. That's interesting, because while the amount of sodium in the control diet was right around 3,000 milligrams per day, the DASH and HF-DASH diets only cut sodium to about 2,700 milligrams per day: usually those following a DASH diet are urged to keep their sodium under 2,400 milligrams/day. 

The primary goal, however, was whether cholesterol scores were improved as much for the HF-DASH as for the standard DASH diet. While the HF-DASH diet and DASH diet both reduced total cholesterol about the same amount, the DASH diet also decreased both LDL and HDL cholesterol. 

With today's knowledge that processed meats are much more dangerous to your health than red meat (whether beef, pork, or venison), one can hardly blame the National Pork Board for funding research into pork products.9 In research looking at 19 clinically obese men and women to participating in a crossover feeding study with an initial 6-week period following one diet was followed by 4 weeks in which they followed their usual diet. Then the participants switched diets and continued for another 6 weeks. 

The comparison diets were DASH-style diets that aimed to provide about 2,500 milligrams of sodium per day and the appropriate amount of calories for the participants to maintain their body weight. The difference was that for one six-week period, the participants consumed the vast majority of their animal protein in the form of chicken and fish; in the other, the main animal protein was pork in the form of pork tenderloin and fresh, uncured, and well-trimmed ham. Both diets permitted the participants to consume 2 servings of lean beef per week. 

The authors tested the blood pressures of all participants at the start and end of the two diets and found that both diets decreased the participants' blood pressures about the same amount. Further testing revealed that total cholesterol decreased more when the participants were following the DASH diet that included pork as opposed to the DASH diet including chicken and fish. 

On the other hand, HDL cholesterol (the good cholesterol) decreased in those following the pork diet, while HDL increased in those following the chicken and fish diet. 

There are drawbacks to this study including its funding and very small size. Regarding the cholesterol results, the authors note that the study was not primarily designed to assess cholesterol changes and suggest that those results should be interpreted "with caution." 


(Continued from Part One)

5. Siervo M, Lara J, Chowdhury S, Ashor A, Oggioni C, Mathers JC. Effects of the Dietary Approach to Stop Hypertension (DASH) diet on cardiovascular risk factors: a systematic review and meta-analysis. Brit J Nutr 2015;113(01):1–15. doi:10.1017/S0007114514003341.

6. Effects of DASH diet on lipid profiles and biomarkers of oxidative stress in overweight and obese women with polycystic ovary syndrome: A randomized clinical trial. Nutrition 2014;30(11-12):1287–1293. doi:10.1016/j.nut.2014.03.008.

7. D SJTP, D CANP. A moderate-sodium DASH-type diet improves mood in postmenopausal women. Nutrition 2012;28(9):896-900. doi:10.1016/j.nut.2011.11.029.

8. Chiu S, Bergeron N, Williams PT, Bray GA, Sutherland B, Krauss RM. Comparison of the DASH (Dietary Approaches to Stop Hypertension) diet and a higher-fat DASH diet on blood pressure and lipids and lipoproteins: a randomized controlled trial. Am J Clin Nutr 2016;103(2):341–347. doi:10.3945/ajcn.115.123281.

9. Sayer RD, Wright AJ, Chen N, Campbell WW. Dietary Approaches to Stop Hypertension diet retains effectiveness to reduce blood pressure when lean pork is substituted for chicken and fish as the predominant source of protein. Am J Clin Nutr 2015;102(2):302–308. doi:10.3945/ajcn.115.111757.

Timothy S. Harlan, M.D.
Dr. Gourmet