Effect of soybean protein on blood pressure: A randomized, controlled trial

Background: Epidemiologic studies suggest that vegetable protein intake is inversely related to blood pressure. Objective: 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. Setting: Three communities in the People's Republic of China. Patients: 302 participants 35 to 64 years of age with an initial untreated systolic blood pressure of 130 to 159 mm Hg, diastolic blood pressure of 80 to 99 mm Hg, or both. Intervention: Study participants were randomly assigned to receive 40 g of isolated soybean protein supplements per day or complex carbohydrate control for 12 weeks; 91.4% completed the intervention. Measurements: Blood pressure measurements were obtained by using random-zero sphygmomanometers at baseline and at 6 and 12 weeks. Results: At baseline, the mean systolic and diastolic blood pressures were 135.0 mm Hg (SD 10.9) and 84.7 mm Hg (SD 6.9), respectively. Compared with the control group, the net changes in systolic blood pressure and diastolic blood pressure were -4.31 mm Hg (95% Cl, -2.11 to -6.51 mm Hg; P < 0.001) and -2.76 mm Hg (Cl, -1.35 to -4.16 mm Hg; P < 0.001), respectively, after the 12-week intervention. The net changes in systolic and diastolic blood pressure reductions were -7.88 mm Hg (Cl, -4.66 to -11.1 mm Hg) and -5.27 mm Hg (Cl, -3.05 to -7.49 mm Hg), respectively, in persons with hypertension and -2.34 mm Hg (Cl, 0.48 to -5.17 mm Hg) and -1.28 mm Hg (Cl, 0.52 to -3.07 mm Hg), respectively, in those without hypertension. Limitations: This trial did not examine whether the blood pressure reduction was due to protein or isoflavones in soybean. Conclusions: Soybean protein supplementation resulted in a reduction in systolic and diastolic blood pressure. These findings suggest that increased intake of soybean protein may play an important role in preventing and treating hypertension.