Clinical Trial of Protein and Blood Pressure

Background: Epidemiologic studies suggest that vegetable protein intake is inversely related to blood pressure.

Objectives: To examine the effect of soybean protein supplementation on blood pressure in persons with prehypertension or stage-1 hypertension

Design: Randomized, double-blind, controlled trial

Study Participants: 350 participants, aged 35-64 years, with an initial untreated systolic blood pressure of 130-159 mmHg and/or diastolic blood pressure of 80-99 mmHg

Intervention: Study participants will be randomly assigned to take 40-grams of isolated soybean protein supplements per day or complex carbohydrate control for 12 weeks.

Outcomes: Blood pressure measurements will be obtained using random-zero sphygmomanometers at baseline and during the trial at weeks 6 and 12. Net changes in systolic and diastolic blood pressure before and after the intervention is the primary outcome.

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