Harvard Gazette: 'Gold standard' of dietary recommendations found

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HARVARD GAZETTE ARCHIVES

'Gold standard' of dietary recommendations found

DASH diet enhancements improve lipids, promote cardiovascular health

In the mid-1990s, researchers at Harvard-affiliated Brigham and Women's Hospital (BWH), Johns Hopkins University, and colleagues presented what is now considered a "gold standard" of dietary recommendations for reducing high blood pressure and "bad" LDL cholesterol. The Dietary Approaches to Stop Hypertension (DASH) diet found that a carbohydrate-rich diet emphasizing fruits, vegetables, and low-fat dairy products and that is reduced in saturated fat, total fat, and cholesterol, substantially reduces blood pressure and "bad" LDL cholesterol. However, the diet also lowered "good" HDL cholesterol and had no effect on triglycerides, both of which are associated with an increased cardiovascular disease risk.

To develop new standards for an even healthier diet, two of the original DASH group, including BWH's Frank M. Sacks, initiated the OmniHeart Randomized Trial (the Optimal Macronutrient Intake Trial to Prevent Heart Disease), which found that among three diets designed to further lower risk, the risk was lowest for people following a diet emphasizing protein and unsaturated fat as opposed to the original DASH diet, which emphasized carbohydrates. These data will be published in the Nov. 16 issue of the Journal of the American Medical Association and simultaneously presented at a late-breaking clinical trials session at the American Heart Association (AHA) Scientific Sessions 2005.

According to Sacks, "Reducing cardiovascular risk is imperative to leading a healthy lifestyle and, while the DASH-low sodium diet remains a hallmark to prevent and treat hypertension, there are additional growing cardiovascular health risks that we need to address. The new recommendations, which include substituting some carbohydrates with protein and fats, can help dramatically reduce the risk factors associated with cardiovascular disease and heart attack."

In this study, researchers enrolled 164 adults, 30 years old and older, and gave them three healthy diets: one diet was rich in carbohydrates (55 percent of calories) and is very close to the DASH diet; the second diet shifted 10 percent of its calories to protein, about two-thirds from plant sources and one-third from chicken and egg whites; the third diet shifted 10 percent of its calories to unsaturated fat, predominantly monounsaturated fat as in olive or canola oils. The study participants all had higher-than-normal blood pressure and about half the subjects were African American, a population that has a greater-than-average risk of developing hypertension.

The researchers found that compared with the participants' usual diet, each of the three diets lowered blood pressure, LDL cholesterol, and estimated coronary heart disease risk. However, the unsaturated fat diet and protein diets both produced improvements over the DASH-like carbohydrate-rich diet.

Specifics include

The protein diet decreased blood pressure among those with hypertension, decreased LDL cholesterol, and decreased triglycerides.

The unsaturated fat diet decreased systolic blood pressure, increased HDL cholesterol, and lowered triglycerides.

Compared with baseline, each diet reduced heart disease risk by 14 to 31 percent. However, the protein and unsaturated fat diets reduced risk substantially more than the carbohydrate diet - 11 to 13 percent in the women, and 12 to 13 percent in the men.

Based on these results, researchers recommend that individuals concerned about high blood pressure and cardiovascular risk should extend the benefits of the original DASH diet by substituting protein or monounsaturated fats for 10 percent of dietary carbohydrates.