Am Fam Physician. 2005 Dec 1;72(11):2344-2349.
Nonpharmacologic treatments for hypertension include weight loss, alcohol and sodium restriction, and aerobic exercise. The only nutritional intervention shown to reduce blood pressure is the Dietary Approaches to Stop Hypertension (DASH) diet, which consists of increases in fruit and vegetable intake and reductions in saturated and total fat. The observation that persons who consume diets high in vegetable protein are less likely to have hypertension has raised the possibility that supplementation might benefit patients with or at risk of developing the disease. He and colleagues conducted a double-blind randomized controlled trial to study the effect of soybean protein supplements in lowering blood pressure in patients defined by the Seventh Report of the Joint National Committee on Prevention, Detection, Evaluation, and Treatment of High Blood Pressure (JNC 7) as having prehypertension (i.e., blood pressure between 120/80 and 139/89 mm Hg) or stage 1 hypertension (i.e., blood pressure of 140/90 to 159/99 mm Hg).
The study population consisted of 302 patients between 35 and 65 years of age recruited at three community health centers in China during blood pressure screening. Blood pressures were determined from an average of nine readings (three observations at three screening visits). Patients were excluded if they reported the use of antihypertensive medications in the previous two months or a history of vascular, renal (serum creatinine ≥1.7 mg per dL [150.3 μmol per L]), pulmonary (with the exception of asthma), psychiatric, or oncologic disease. Women who were pregnant and patients with alcohol intake greater than 21 drinks per week also were excluded. The remaining patients were randomly assigned to consume a 40-g soybean protein or complex carbohydrate wheat supplement in indistinguishable “cookies” daily for 12 weeks. Patients were instructed to reduce other food intake (most consumed the cookies in place of their usual breakfast or lunch) but not to change their usual patterns of physical activity or alcohol intake during the study.
There were no significant differences between the two groups in weight, height, waist circumference, blood pressure values, or 24-hour urinary excretion of sodium and potassium. Data collection was repeated at six and 12 weeks post-randomization. At both follow-up visits, all unconsumed cookies were collected to measure adherence. Side effects were assessed at the 12-week visit using a questionnaire. About 93 percent of participants taking the soybean protein supplement and 90 percent of participants in the control group completed the study. Cookie consumption exceeded 92 percent in both groups.
The study’s key finding was a statistically significant difference in systolic and diastolic blood pressure reductions between the intervention and control groups at 12 weeks. Although both groups experienced reductions in blood pressures, patients consuming the soybean protein supplement had greater decreases in systolic and diastolic blood pressures (4.31 and 2.76 mm Hg, respectively) than did subjects in the control group. This difference could not be explained by potentially confounding variables such as body weight or fat consumption, which were similar between groups. Incidences of gastrointestinal side effects also were similar.
The authors conclude that a soybean protein supplement was more effective at lowering blood pressure after 12 weeks than a complex carbohydrate supplement. On the basis of this data, they suggest that soybean protein may be an effective alternative to standard medications for otherwise healthy patients with mild, or stage 1, hypertension. They caution, however, that differences in the major type of dietary protein consumed by Chinese and U.S. populations (i.e., plant versus animal) could affect the applicability of these results.
He J, et al. Effect of soybean protein on blood pressure: a randomized, controlled trial. Ann Intern Med. July 5, 2005;143:1–9.
editor’s note: Although this study is an important contribution to the meager evidence base on dietary interventions for hypertension, its short follow-up period and otherwise healthy subjects call into question the long-term effectiveness of soybean protein supplements in patients with one or more chronic medical conditions. More intriguing is the possibility of using these supplements for hypertension prevention in patients at high risk, although an editorial1 in the same issue points out that the data in the prehypertensive subgroup did not reach statistical significance. Further studies are required to establish more conclusively the link between soybean protein and blood pressure before we can recommend this therapy to large groups of patients.—k.w.l.
1. Cutler JA, Obarzanek E. Nutrition and blood pressure: is protein one link? Toward a strategy of hypertension prevention. Ann Intern Med. 2005;143:74–5.
Copyright © 2005 by the American Academy of Family Physicians.
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