The study is the first to directly compare the effects of vegetable protein, dairy protein, and carbohydrates on hypertension.

Study participants who took low-fat protein supplements derived from either milk or soy had lower blood pressure readings than participants who took carbohydrate supplements.

While this difference was modest, the researchers say it could mean a 6% drop in stroke deaths and a 4% drop in deaths from heart attack.

"Our study suggests that partially replacing a high-carbohydrate diet with soy or low-fat dairy may be beneficial for blood pressure," says study researcher Jiang He, MD, PhD, of Tulane University.

About 75 million Americans have high blood pressure, according to the American Heart Association.

Some earlier studies have suggested that eating a diet rich in low-fat dairy products can lower blood pressure. The most well-known of these studies was the Dietary Approaches to Stop Hypertension (DASH) diet study. It found that lowering sodium, limiting red meats and sweets, and eating two to three daily servings of low-fat dairy could reduce hypertension.

However, other studies have not shown the association, and some others have even suggested that a high-carbohydrate diet lowers blood pressure.

In an effort to better understand the impact, if any, of dietary protein and carbohydrates on blood pressure, Jiang He and colleagues conducted a study involving 352 patients with prehypertension or moderate hypertension (systolic blood pressure ranged from 120 to 159 and diastolic of 80 to 95).

Each study participant took powdered supplements of soy protein, milk protein, or refined carbohydrate in liquid twice a day for eight weeks. Milk and soy supplementation delivered 40g of protein daily, while the protein in the carbohydrate powder was negligible.

After a three-week "wash out" period, the participants were put on another supplement for eight more weeks, followed by another three-week period without supplementation and another eight weeks on the third supplement.

Each participant took all three supplements over the course of the study, and since the powders looked and tasted the same, neither they nor the investigators knew which one they were taking at any given time.

The supplements were formulated to allow the researchers to compare the effects on hypertension without changing other dietary influences on blood pressure, including sodium, potassium, and calcium.

Blood pressure readings were taken three times at each of two clinical visits before and after each eight-week treatment phase.

While no change in diastolic pressure was seen, milk protein supplementation was associated with an average lowering of 2.3 points in systolic blood pressure, and soy supplementation was associated with a 2.0 point reduction, compared to carbohydrate supplementation.

The study, which was funded by the National Heart Lung and Blood Institute, appears in the August 2 issue of Circulation.

From the July 19, 2011, Prepared Foods' Daily News.