Clinical Trial of Dietary Protein and Blood Pressure

BACKGROUND:

At least 50 million adult Americans have high BP, which is one of the most important modifiable risk factors for coronary heart disease, stroke, and end-stage kidney disease. Nutrient intake has been related to the development of high BP, and nutritional modifications have become an important approach for the treatment and prevention of high BP. While the effect of sodium, potassium, and alcohol on BP has been studied extensively, the effect of dietary macronutrients, such as protein, has not been as well studied. Results from this study may provide justification for recommending protein supplements for the prevention and treatment of high BP in the general population.

DESIGN NARRATIVE:

The study will enroll 280 healthy participants with BP levels higher than optimal or with stage-1 hypertension (systolic BP of 120-159 mm Hg and diastolic BP of 80-95 mm HG). Participants will be recruited by a mass mailing and a worksite/community-based BP screening in New Orleans, Louisiana, and Jackson, Mississippi. Following a two-week screening period, eligible participants will receive either 40 grams of soy protein, 40 grams of milk protein, or 40 grams of complex carbohydrates (control) daily for eight weeks. Following those eight weeks, participants will not receive any supplements for three weeks. Participants will then repeat the process with the other two supplements. The primary outcome will be difference in BP during the soy protein supplementation, milk protein supplementation, and placebo control phases. In addition, changes in serum lipids; waist and hip circumference; and fasting plasma insulin, glucose, leptin, and homocysteine will be monitored and examined in terms of impact on BP level.

Inclusion criteria

• Systolic BP of 120 to 159 mm Hg and diastolic BP of 80 to 95 mm Hg (average of 6 measurements at 2 screening visits)
• Willing to participate in all aspects of the study

Exclusion criteria

• Consumption of dietary protein greater than or equal to 1.63 grams/kg per day, as determined by two 24-hour dietary recalls
• Stage-2 or higher severe hypertension (systolic BP greater than or equal to 160 mm Hg and/or diastolic BP greater than or equal to 95 mm Hg)
• Use of antihypertensive medications or medications that affect BP
• History of clinical heart disease (e.g., angina/heart attack, coronary revascularization, heart failure, stroke/transient ischemic attack, peripheral arterial disease)
• Kidney disease (serum creatinine level greater than or equal to 1.7 mg/dL for men and greater than or equal to 1.5 mg/dL for women)
• Current hypercholesterolemia (fasting serum total cholesterol greater than or equal to 240 mg/dL) or use of cholesterol-lowering medications
• Current diabetes (fasting serum glucose greater than or equal to 126 mg/dL) or use of insulin or oral hypoglycemic agents
• Severe obesity (body mass index greater than or equal to 40 kg/m²)
• Current use of prescription weight loss medications, underwent weight loss surgery, and/or experienced weight loss greater than 15 pounds within the 6 months prior to study entry
• Cancer (except non-melanoma skin cancer) that required treatment during the year prior to study entry
• Consumption of more than 14 alcoholic beverages per week
• Current participation in another medical study
• Consumption of milk or soy protein greater than or equal to the 90th percentile of intake in the U.S. general population
• Has another member of the household participating in the study
• Study employees or living with study employees
• Allergy or intolerance to soy protein or milk protein products
• Allergy to aspartame
• Plans to move out of the study area (greater than or equal to 50 miles from the study site) and has difficulty coming to the study site
• Inability or unwillingness to cooperate during the screening visits
• Poor compliance during the screening period (intake of less than 85% of supplements)
• Pregnant or plans to become pregnant during the study