The DASH Diet: Is It Feasible for Everyone

Disclosure: For Jaimie Hunter, Alain Bertoni, and David Goff: Pending NIH grant "Translative Dietary Trials Into the Community."
Pub Date: Wednesday, June 11, 2008
Authors: Jaimie C. Hunter, MPH Alain G. Bertoni, MD, MPH David C. Goff, Jr, MD, PhD

Fung TT, Chiuve SE, McCullough ML, Rexrode KM, Logroscino G, Hu FB.,  Adherence to a DASH-style diet and risk of coronary heart disease and stroke in women.,  Archives of internal medicine, 168 (7) 713-20. View in PubMed(link opens in new window)

The Dietary Approaches to Stop Hypertension (DASH) diet, a carbohydrate-rich eating plan that emphasizes fruits, vegetables, and low-fat dairy products while reducing saturated fat, total fat, and cholesterol by decreasing consumption of red meat, sweets, and added sugars [1], has been evaluated in several studies to determine its effectiveness for lowering blood pressure. The original studies testing DASH were feeding trials in which participants were provided with DASH foods and closely monitored. Results of these trials have indicated positive effects of the DASH diet for reducing systolic and diastolic blood pressure among normotensive adults and in adults with stage 1 hypertension [1,2] and showed improvements in low-density lipoprotein cholesterol levels.[3] The DASH feeding trials demonstrated that, when provided with DASH foods, participants could considerably reduce their risk factors for cardiovascular disease. Several studies have suggested that individuals can also successfully adopt the DASH diet and achieve health benefits when they purchase and/or prepare the foods themselves. The Prospective Registry Evaluating Outcomes After Myocardial Infarction: Events and Recovery (PREMIER) study implemented DASH via a group-based intervention, teaching participants to purchase and prepare DASH foods.[4] Similar to the original DASH feeding trials, improvements in blood pressure levels were observed in PREMIER. The impact of the DASH diet on blood pressure levels was less significant in PREMIER. However, PREMIER was not a feeding study; thus, adherence to the DASH diet among PREMIER participants may have been lower than adherence in the original DASH feeding studies.[2,4,5]

Despite the known benefits of the DASH diet, adherence in the general population has been limited. Uptake of the DASH diet in observational studies has been associated with lower risk for chronic disease. For example, using data from the National Health and Nutrition Examination Survey (NHANES) from 1988 to 1994 and 1999 to 2004, Mellen and colleagues found that, among over 4000 participants with known hypertension, less than 20% were classified as accordant with the DASH diet.[6] Accordance with the DASH diet was associated with older age, nonblack ethnicity, higher education, lower body mass index, and known diabetes mellitus. A recent paper by Fung and colleagues [7] highlighted associations between adherence to the DASH-style diet and risk of coronary heart disease (CHD) and stroke in women, using data from the Nurses' Health Study. The Nurses' Health Study, which began in 1976 and included over 120,000 female nurses aged 30 to 55 years at baseline, has been collecting data biennially via questionnaires on medical, lifestyle, and other health-related information.[8] In their paper, Fung and colleagues used Nurses' Health Study data from women who had follow-up data from 1980 to 2004 and who had completed a food frequency questionnaire (FFQ) in 1980. Using the FFQ, the group constructed a DASH diet adherence score that classified women into quintiles according to their self-reported intake of components in the DASH-style diet. The group also identified incident cases of chronic disease over the 24-year follow-up period, including 2317 cases of CHD and 2317 cases of stroke. Fung and colleagues also observed an inverse association between the DASH diet adherence score and risk for CHD and stroke. Analyses stratified by major risk factors at baseline indicated a stronger association between DASH diet adherence score and CHD among normal weight women compared to overweight women and among current smokers compared to nonsmokers. They also found that women with higher DASH diet adherence scores were more likely to use multivitamins, exercise more, consume more fiber and omega-3 fatty acids, and consume less trans fat, saturated fat, and total energy. Analyses of associations between DASH diet adherence score and personal characteristics (e.g., education, socioeconomic status [SES]) were not included.

The approach taken for constructing the DASH diet adherence score is a major limitation to this study. Incomplete data made it difficult to take into account specific intake levels for each food group according to energy requirements for individuals because these data were not available. Also, all food groups were given equal weight in the overall score since, as the authors noted, it was difficult to specify the contribution of specific food groups to disease risk. The population included in the Nurses' Health Study is fairly homogeneous - 98% are white women who likely have similar education and income levels - thus limiting the generalizability of the findings from the Fung et al. study. Nevertheless, these findings extend research from the previous DASH and PREMIER trials and indicate that, in addition to an impact on blood pressure and cholesterol levels, the DASH diet may also have a positive impact on decreasing risk for cardiovascular disease. Additional research is needed to determine whether this finding also holds true for men and other race/ethnicity and SES subgroups.

A common critique of randomized, controlled trials is that participants are highly selected, and interventions are intensive and complex, such that the findings from these trials may not be generalizable.[9] This is an important concern with respect to nutritional interventions, as there is substantial literature describing the influence of economics and other structural factors, as well as individual skill levels, on unhealthy food consumption patterns. For example, in the United States, the supply of refined grains, added fats, and added sugars on a per-capita basis exceeds the US Department of Agriculture's per-capita dietary recommendations by a wide margin; however, the actual supply and availability of fruits, vegetables, and dairy are less than the seven servings/day recommended.[10] As a result of this imbalance, calorie-dense foods are inexpensive, while more nutritious foods are comparatively more expensive.[11] In fact, statistical modeling suggests that "low income consumers' food choices are quite rational from an economic standpoint...once food costs are taken into account."[12] There is also substantial evidence that residents of lower income and/or minority areas have less access to healthier foods in their own neighborhoods. Such neighborhoods are less likely to have supermarkets and more likely to have fast food restaurants; moreover, the quality of fruits and vegetables available in local stores is poorer than in wealthier and/or nonminority areas.[13] Perhaps, therefore, it should not be surprising that cost is frequently cited as a reason for decreased adherence or nonadherence to DASH and similar diets in these communities.[14] In addition, food-related knowledge and skills may be different among individuals within low-SES and low-education groups, and this may impact their ability to adopt healthy diets. Nevertheless, preparing foods from scratch has been associated with more adequate dietary intakes and greater food security.[15] Greater cooking skills have been associated positively with fruit and vegetable intake and negatively with use of convenience foods.[16]

Recently, the research community has begun to pay increased attention to translational research, or opportunities to translate scientific findings into practical applications. Additional research is needed to translate the DASH trial results, including devising effective strategies for increasing uptake of and adherence to the DASH diet among individuals in community-based settings. The potential impact of successful adoption of the DASH diet on heart disease risk is substantial - if the US population were to experience the first DASH trial effect (lowering systolic blood pressure by 5.5 mm Hg), 668,000 CHD events could be prevented over 10 years.[17] In spite of this promise, there are very few reports in the published literature describing attempts to translate the DASH diet in community-level interventions.[18,19] The National Heart Lung and Blood Institute (NHLBI) has a website dedicated to the DASH diet and geared toward the public. NHLBI also developed "Your Guide to Lowering Your Blood Pressure with DASH," a 56-page booklet that describes the DASH trials in simple terms and explains the dangers of high blood pressure. It breaks the DASH diet into specific meal patterns, describing caloric goals and daily serving suggestions from each of the food groups, and provides simple examples of foods that are allowed and encouraged on the diet. A menu guide and a series of recipes are also provided. These resources provide the necessary first steps toward adopting the DASH diet for a certain proportion of the population but may not be effective at changing dietary behaviors among individuals who are most in need of the DASH diet, including low-income individuals. Additional research is needed to determine the extent to which individuals in community-based settings can feasibly implement the DASH diet, as well as the acceptability of the DASH diet among individuals in the community.

Questions that should be answered in future research include:

• What are the existing or underlying attitudes or norms within families or the community that facilitate or hinder adoption of the DASH diet?
• What resources exist in the homes of individuals in community-based settings that would either enhance or reduce the ability to prepare foods using the DASH diet?
• What food resources exist in community-based settings that provide access to foods included in the DASH diet?
• Are the materials currently available for disseminating the DASH diet feasible and acceptable for use in various community-based settings? These questions could lead to trials that would determine whether the DASH diet could be effectively adopted in community-based settings and, if so, ascertain the impact of the DASH diet on chronic disease outcomes among individuals in these settings. Answers to these questions could also lead to environmental and policy-level changes that would improve the availability of healthy food options for all communities, thus leading to improvements for a host of health outcomes associated with healthy diets (e.g., obesity, stroke, and diabetes mellitus).

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-- The opinions expressed in this commentary are not necessarily those of the editors or of the American Heart Association. --