Effect of Soybean Protein on Blood Pressure: A Randomized, Controlled Trial

Context Observational studies suggest that higher intake of vegetable protein is associated with lower blood pressures. Contribution This double-blind trial from China randomly assigned 302 adults with high-normal or mildly elevated blood pressures (... show more

Context Observational studies suggest that higher intake of vegetable protein is associated with lower blood pressures. Contribution This double-blind trial from China randomly assigned 302 adults with high-normal or mildly elevated blood pressures (diastolic blood pressure of 80 to 99 mm Hg, systolic blood pressure of 130 to 159 mm Hg, or both) to daily cookies containing 40 g of either soybean protein or complex carbohydrates. At 12 weeks, soybean cookies reduced diastolic and systolic blood pressure values by about 3 to 4 mm Hg more than did the carbohydrate cookies. Cautions The follow-up duration was short. Implications Soybean protein supplementation might help lower blood pressure in some people. The Editors Hypertension has become a global public health challenge, affecting approximately 50 million individuals in the United States and 1 billion individuals worldwide (1, 2). The prevalence of hypertension has increased dramatically in developing countries during the past several decades (1, 3) and has increased slightly in the United States according to a recent national survey (4). Hypertension is not only very common but is also an important major modifiable risk factor for cardiovascular disease, stroke, and chronic kidney disease (5-7). Lifestyle modification, including nutritional intervention, provides an important approach for preventing and treating hypertension (2, 8). Clinical trials have documented that weight loss, exercise, alcohol restriction, sodium reduction, and potassium supplementation reduce blood pressure in both hypertensive and prehypertensive persons (2, 8). The effect of dietary macronutrients on blood pressure has not been well studied, although clinical trials indicate that diets rich in fruits, vegetables, and low-fat dairy products and with reduced saturated and total fat (Dietary Approaches to Stop Hypertension [DASH] diet) lower blood pressure (9). Several epidemiologic studies have observed an inverse relationship between dietary protein intake and blood pressure (10-14). The few clinical trials that examined the effect of an increased intake of dietary protein on blood pressure produced conflicting results (10, 15, 16). In most of these trials, change in blood pressure was not the primary outcome of interest, the sample size was small, and only a single blood pressure measurement was obtained at the baseline and termination visits (10). We conducted a randomized, double-blind, controlled multicenter trial to test the effect of soybean protein supplementation on systolic and diastolic blood pressure among individuals with prehypertension or stage 1 hypertension in 3 samples of community residents in the People's Republic of China. Methods Our study was a randomized, double-blind, complex carbohydratecontrolled multicenter clinical trial designed to test the efficacy of 40 g of isolated soybean protein supplementation per day in lowering systolic and diastolic blood pressure among individuals with prehypertension or stage 1 hypertension. Three clinical centers in the People's Republic of China, located in Beijing, Xiulo (Hebei province), and Wuhan (Hubei province), participated in the trial. Demographic characteristics and lifestyle, including dietary habits, were similar in the 3 communities. In Beijing, the clinical center used a 2 2 factorial design to assign the study participants to soybean protein and potassium (60 mmol/d) interventions (17). The other 2 centers used a 2-group parallel design to assign the study participants to soybean protein supplements or a complex carbohydrate control. Investigators obtained informed consent before the initial screening visit and before randomization. The institutional review boards at the Tulane University Health Sciences Center and the Cardiovascular Institute of the Chinese Academy of Medical Sciences approved the protocol. Study Participants Trial participants were men and women 35 to 65 years of age who had an average systolic blood pressure of 130 to 159 mm Hg, diastolic blood pressure of 80 to 99 mm Hg, or both based on an average of 9 readings (3 observations at each of 3 screening visits). The criteria for exclusion were self-reported use of antihypertensive medications in the previous 2 months; a history of cardiovascular disease, diabetes mellitus, cancer, chronic obstructive pulmonary disease, psychiatric disease, or any other serious life-threatening illness that required regular medical treatment; serum creatinine level of 150.3 mol/L or greater (1.7 mg/dL) at the screening examination; or alcohol intake of 21 drinks or more per week or at least 40 g/d. We also excluded women who were pregnant or who intended to become pregnant during the study. The study sites conducted community-based blood pressure prescreening to recruit the trial participants. We invited 862 persons who met blood pressure and other criteria at prescreening and who were willing to participate in the trial to the study clinics for screening visits. Of them, 302 persons met all eligibility criteria and were randomly assigned (Figure 1). Of the 302 trial participants, 150 were recruited from Beijing, 84 were recruited from Hebei province, and 68 were recruited from Hubei province. Figure 1. Study participant flow chart. Intervention We randomly allocated 150 study participants to soybean protein supplementation and 152 study participants to the control group by using a computer-generated scheme. We stratified the randomization by clinical site and used a block size of 4. We also stratified the randomization by potassium supplementation allocation at the Beijing clinical site, resulting in an equal proportion of study participants receiving potassium intervention in the soybean protein supplement group (37 of 74 participants) and the control group (38 of 76 participants). An effect of an interaction between soybean protein and potassium supplementation on blood pressure was not evident. The randomization assignment schedule wa show less