Effect of soybean protein on novel cardiovascular disease risk factors: a randomized controlled trial

Randomized controlled trial in adults with elevated blood pressure recruited from New Orleans, Louisiana and Jackson, Mississippi. Participants were men and women without a history of cardiovascular disease or major chronic illness and were not taking antihypertensive medications. For the soy protein group, n=83; for the milk protein group, n=81; allocation was fixed 1:1:1 across three sequences.

Soy protein 40 g/day (89.3 mg isoflavones) was taken twice daily in water or juice for 8 weeks. Comparator arms received 40 g/day milk protein or 40 g/day carbohydrate; the milk protein supplement contained 10 mg cholesterol per serving.

Soy protein produced limited but favorable biomarker changes. Compared with carbohydrate, soy significantly reduced leptin (−2089.8 [−3689.3, −490.3], p=0.011) but did not significantly change E-selectin (−0.74 [−3.79, 2.30], p=0.63) or resistin (−0.02 [−1.46, 1.42], p=0.98). Compared with milk protein, soy significantly lowered E-selectin (−3.93 [−7.05, −0.81], p=0.014) but not leptin (−656.5 [−2298.2, 985.3], p=0.43) or resistin (0.71 [−0.74, 2.15], p=0.34). Most other inflammatory and endothelial biomarkers, including CRP, IL-6, TNF-a, VCAM-1, ICAM-1, thrombomodulin, and adiponectin, showed no meaningful changes. The authors concluded that soy protein may have beneficial effects on endothelial and metabolic function.

The intervention was short at 8 weeks and assessed biomarkers rather than clinical cardiovascular outcomes, so durability and clinical significance remain uncertain. Several endpoints were null or only borderline significant, and the trial was conducted in a relatively selected population from two U.S. centers, which may limit generalizability.