American Society For Nutrition

A DASH of reality – translational research in nutrition

A DASH of reality – translational research in nutrition

Excellence in Nutrition Research and Practice
Posted on 02/08/2011 at 02:51:03 PM by Student Blogger
By: Mitch S.

The Dietary Approaches to Stop Hypertension clinical trials revealed that diets higher in fruits, vegetables, grains and low-fat dairy products could reduce blood pressure(1) – even in the presence of a higher sodium diet(2). The DASH studies were exemplary in their design and execution; the sponsor NIH-NHLBI and the myriad investigators involved should be proud of their accomplishments. Controlled feeding studies are to nutrition research what the randomized, double blind, placebo controlled trial is to pharmaceutical research - challenging to execute, but critical to examining causation.

Marlene Most revealed that the DASH diet was also rich in phytochemicals from the additional fruits, vegetables, grains, nuts and spices(3). These phytochemicals may be critical to the DASH diet benefits.  My doctoral work focused on the specific effects of a phytochemical-enriched diet using table grapes as a model in hypertensive rats.  Not only did grape intake reduce blood pressure, but it also reduced many eventual effects of hypertension including an enlarged heart and kidneys, stiffening of the heart walls, and reduced heart function(4). In humans, compliance with a phytochemical-rich diet like the DASH diet may have similar long-term benefits.

My post-doctoral fellowship focuses on clinical research and didactic training in trial design, trial execution and data analysis. I am very fortunate to participate in a study with the department of cardiology – the impact of the DASH diet on hypertensive patients with diastolic heart failure. In a controlled feeding design, subjects are provided with a DASH-style diet for three weeks, after which we measure changes in cardiac and renal function. While my clinical colleagues in the study are focused on clinical efficacy, my focus is on the “success” of this short-term intervention relative to that of the parent DASH trials. Compared to data from their baseline assessments, do the provided meals confer a 3-fold increase in fruit and vegetable intake and increased phytochemical intake? Which phytochemicals? How do these phytochemicals correlate with the clinical cardiac and renal outcomes?

In my bench research, I tightly control the diet of my furry subjects – both what they eat and how much they eat. Furthermore, these parameters can be recorded with great accuracy. But as a clinical researcher, my influence over subject dietary habits is very limited. Even if subjects are provided food, their intake could vary and they could consume additional items. In addition, human studies are riddled with confounders not found with animal models .  My experiences have also revealed other challenges. Food intake in aging subjects is affected by altered taste and dentition, and accurate diet recall is affected by memory. Some subjects even require assistance filling in their food frequency questionnaire – bubble forms are not ideal for arthritic fingers!

Dietary intervention studies are expensive and labor-intensive, but the results can propel nutrition science. While my work has become much more complex, I feel blessed for the opportunity to take my research from “bench to bedside”.
1.    Appel LJ, Moore TJ, Obarzanek E, et al. A clinical trial of the effects of dietary patterns on blood pressure. DASH Collaborative Research Group. N Engl J Med. 1997;336:1117-1124.
2.    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. DASH-Sodium Collaborative Research Group. N Engl J Med. 2001;344:3-10.
3.    Most MM. Estimated phytochemical content of the dietary approaches to stop hypertension (DASH) diet is higher than in the Control Study Diet. J Am Diet Assoc. 2004;104:1725-1727.
4.    Seymour EM, Singer AA, Bennink MR, et al. Chronic intake of a phytochemical-enriched diet reduces cardiac fibrosis and diastolic dysfunction caused by prolonged salt-sensitive hypertension. J Gerontol A Biol Sci Med Sci. 2008;63:1034-1042.

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