People with prehypertension or stage 1 hypertension experienced a significant drop in both systolic and diastolic blood pressure after taking a daily 40g isolated soybean protein supplement for 12 weeks.
A control group, taking a complex carbohydrate for 12 weeks, saw no such benefit.
The net change in blood pressure was most pronounced among soy group subjects with blood pressures of at least 140/90 mmHg, write the researchers in the 5 July issue of the Annals of Internal Medicine (vol 143, pp 74-75).
High blood pressure is a major risk factor for heart disease, and recent evidence suggests that it is increasing across the globe, with more than 1.5 billion people expected to have high blood pressure by 2025 (around one in three adults over the age 20).
Researchers are increasingly looking at dietary intervention to high blood pressure, with evidence for the positive effect of milk proteins on hypertension leading to new functional foods.
number of small-scale clinical trials have previously suggested that short-term soy consumption can lower blood pressure too but the researchers say that most of these studies have not been well designed.
For the new trial, Dr Jiang He of Tulane University in New Orleans and Chinese colleagues recruited 302 adults living in China with systolic pressures between 130 and 159 mmHg or diastolic pressures of 80 to 99 mmHg, or both. They were between 35 to 64 years of age.
The results "provide new evidence supporting dietary soybean protein supplementation to prevent and treat hypertension," they write.
In a related editorial, Dr Jeffrey A. Cutler and Dr Eva Obarzanek of the National Heart, Lung, and Blood Institute in Bethesda, Maryland, warn that while the new study provides "another important link between blood pressure and dietary macronutrient intake," further studies are needed before soybean supplements can be recommended to hypertensive patients.
The current trial did not examine whether the blood pressure reduction was due to protein or isoflavones in soybean and therefore further work is needed to identify the mechanism for the benefit.
In May, new research assessing the effect of soy intake over two to three years found that it was inversely associated with both systolic and diastolic blood pressure, particularly among elderly women.