This is the eleventh entry in a six-week series of topics following the syllabus of my Human Nutrition & Obesity graduate summer course. Each entry offers a snapshot or principal take home message from that lecture. This lecture was entitled: Fruits and Vegetables. @tgs777 or @GUFoodStudies
If the Mediterranean diet had a slightly lower fat sibling or nom de plume, it would be the DASH Diet, for dietary approaches to stop hypertension. The Dietary Approaches to Stop Hypertension study “was a multicenter, randomized feeding study that tested the effects of dietary patterns on blood pressure.” As with studies using the Mediterranean diet, the real value of the DASH Diet studies is that it is a trial of dietary patterns rather than individual nutrients; thus it investigates the effects of real food on blood pressure.
The study enrolled 459 adults with, by today’s definition, moderate or pre-hypertension, having systolic blood pressures of less than 160 mm Hg and diastolic blood pressures of 80 to 95 mm Hg. For three weeks, the subjects were fed a control diet that was low in fruits, vegetables, and dairy products, with a fat content typical of the average diet in the United States. They were then randomly assigned to receive for eight weeks:
(1) Control diet: the nutrient composition was typical of the diets of a substantial number of Americans. The potassium, magnesium, and calcium levels were close to the 25th percentile of U.S. consumption.
(2) Fruits-and-vegetables diet: provided potassium and magnesium at levels close to the 75th percentile of U.S. consumption, along with high amounts of fiber. This diet provided more fruits and vegetables and fewer snacks and sweets than the control diet but was otherwise similar to it.
(3) Combination diet (DASH Diet): rich in fruits, vegetables, and low-fat dairy foods and had reduced amounts of saturated fat, total fat, and cholesterol. This diet provided potassium, magnesium, and calcium at levels close to the 75th percentile of U.S. consumption, along with high amounts of fiber and protein.
In what is now a classic finding that has been repeatedly confirmed, a diet rich in fruits and vegetables results in significant decreases in systolic and diastolic blood pressures. (see figure at left). As this diet is supplemented with additional protein and fiber, essentially further decreasing the glycemic index of the diet, additional decreases in blood pressure are realized. In quantitative terms, the reductions with the fruits-and-vegetables diet were 2.8 mm Hg (P<0.001) and 1.1 mm Hg greater than with the control diet (P = 0.07). The combination diet reduced systolic blood pressure by 5.5 mm Hg more and diastolic blood pressure by 3.0 mm Hg more than the control diet did (P<0.001 for each).
In 1995, when the DASH Diet was published, the impact of a fruit and vegetable diet on blood pressure was revolutionary, and this study essentially ushered in the era of nutritional approaches to chronic disease and food as medicine. It is important to note that the blood pressure lowering effects of the DASH Diet are as great, and frequently greater, than typical first-line antihypertension medications. For more details on the DASH Diet, see the DASH Eating Plan.
It is also important to note that the DASH Diet was conducted in the era of the low-fat diet, when significant blame for heart disease and hypertension was still targeted at fat intakes in general, and saturated fat intakes in particular. Since then, research has identified the greater impact of decreased intakes of polyunsaturated fats on increases in blood pressure.
Thus, as significant as the findings of DASH Diet are, the liberal consumption of seafood, fish oil, and olive oil in the Mediterranean diet result in even greater decreases in blood pressure and offer, I believe, the best pattern of food consumption (and tastiest!).