Should We Be Adding Fat to the DASH Diet?

Author:

Elaine M. Hinzey, RD, LDN

A study done at the University of California, San Francisco Benioff’s Children’s Hospital Oakland Research Center and published in the American Journal of Clinical Nutrition compared a higher-fat DASH diet (HF-DASH) to the traditional DASH diet.

The DASH diet is known to bring down blood pressure, low-density lipoprotein (LDL) cholesterol, and high-density lipoprotein (HDL) cholesterol. Furthermore, when saturated fat is substituted for carbohydrate and unsaturated fat, many studies have shown that LDL levels increase. 

In this study, researchers placed participants on a control, DASH, and HF-DASH diet for three weeks each with a two-week wash-out period between phases. In total, 36 participants completed all three diet periods. The HF-DASH diet included full-fat dairy, which obviously increased total and saturated fat content of the diet, while decreasing carbohydrate content. Participants also avoided fruit juice and other forms of concentrated sugar while adhering to the HF-DASH diet. 

The control diet was lower in fiber, fruit, and vegetables and higher in red meat than either the DASH or the HF-DASH diets. 

The researchers state that the HF-DASH diet decreased triglyceride levels, as well as medium and large LDL particle levels, compared to the DASH diet. However, no significant differences in LDL response were found. Blood pressure decreased similarly in the DASH and HF-DASH diet, compared to the controlled diet. 

As pointed out by Marion Nestle, PhD, the study was supported by Dairy Management Inc. and by the National Center for Research Resources and the National Center for Advancing Translational Sciences, and an NIH grant, through the University of California, San Francisco Clinical & Translational Science Institute. Ronald M. Krauss, an author of the study, had previously received and is currently receiving research funding from the Dairy Management Inc. for this and other projects. 

Non-interventional and randomized clinical trials have demonstrated conflicting results regarding the effect of calcium intake on blood pressure and weight (these results have varied from null to protective). Some studies suggest that the alpha-linoleic acid in full-fat dairy has an inverse relationship with blood pressure. A few researchers have suggested that it is not the calcium that improves blood pressure, but the magnesium and potassium in these dairy foods. 

The National Heart, Lung, and Blood Institute (NHLBI) Family Heart Study was a multicenter, population-based study to identify and evaluate genetic and non-genetic causes of coronary heart disease, preclinical atherosclerosis, and cardiovascular risk factors. A total of 4,797 participants had their dairy consumption assessed via self-administered, semi-quantitative food frequency questionnaires. They also had their resting blood pressure checked three times. Information regarding cigarette usage, alcohol usage, physical activity, and education was obtained by interview. The mean age of participants was 52.2 + 13.7 and 45% of the participants were male, while 4% were black. The researchers found that the people with the highest intake of dairy had the highest education level and also ate the most fruit and vegetables. Compared with participants who consumed < 2 servings of dairy products each day and < 0.68 grams of alpha-linoleic acid each day, higher consumption of alpha-linoleic acid was associated with a 19% lower prevalence of hypertension in a multivariable model. Consuming > 2 servings of dairy foods each day was associated with 26% lower hypertension prevalence odds. Higher total alpha-linoleic acid and dairy product intake was associated with 35% lower prevalence odds of hypertension. The inverse relation between dairy and hypertension seemed to be independent of calcium. A serving of dairy for the purposes of this study was considered to be 8 ounces of low-fat or whole milk, 1 cup of yogurt, a half cup of cottage cheese, or 1 slice of cheese. Participants were asked how often they consumed these foods: 1-3 times a month, 1 time a month, 2-4 times a week, 5-6 times a week, 1 time a day, 2-3 times a day, 4-6 times a day, or > 7 times a day. 

In a study published in Hypertension done by Lu Wang MD, PhD of Brigham and Women’s Hospital and her colleagues, the incidence of hypertension decreased 11% among women who ate the most low-fat dairy. Unlike some other studies, the researchers felt that this improvement was entirely accounted for by calcium, although calcium and vitamin D supplements had no effect on blood pressure. 

In the Women’s Health study, which involved 28,886 health professionals with a mean age of 53.8 and no cardiovascular disease or hypertension at baseline, a semi-quantitative food frequency questionnaire was used to assess dairy intake. After ten years of follow-up, hypertension risk was lowest for those who had the highest dairy intake at baseline. The relationship continued after adjusting for age, race, randomized treatment, and total energy intake. In this study, high-fat dairy had little impact on blood pressure, but hypertension risk fell 16% among those with the highest intake of low-fat dairy compared to those with the lowest. The researchers speculated that saturated fat might mitigate the beneficial effects of other components in dairy foods, including calcium. The link between low-fat dairy and lower blood pressure was mediated by dietary calcium intake, which substantially attenuated the association. The association was only slightly attenuated by controlling for lifestyle factors, clinical factors, and other dietary factors, including vitamin D intake. 

For now, high-fat dairy food should not be recommended as a means for decreasing blood pressure. The research remains cloudy and there is too much conflicting evidence to make any firm decisions. 

Research and recommended reading

CHORI study finds higher fat variation of DASH diet lowers blood pressure, triglycerides. Eurekalert website. http://www.eurekalert.org/pub_releases/2016-01/chr-csf010816.php. Published January 11, 2016. Accessed February 29, 2016.

Djoussé L, Pankow JS, Hunt SC, Heiss G, Province MA, Kabagambe EK, Ellison RC. Influence of saturated fat and linoleic acid on the association between intake of dairy products and blood pressure. Hypertension. 2006;48(2):335-41. doi:10.1161/01.HYP.0000229668.73501.e8.

Nestle M. Five more studies related to food-industry sponsorship. Food Politics website. http://www.foodpolitics.com/tag/sponsored-research/. Accessed February 14, 2016. 

Phend C. Dairy does the blood pressure good. Medpage Today website. http://www.medpagetoday.com/Cardiology/Hypertension/8293. Published February 11, 2008. Accessed February 29, 2016.