Effect of Soy Protein Supplementation on Serum Lipids:
A Randomized, Controlled Clinical Trial
Clinical trials have indicated that soy protein supplementation reduces blood cholesterol in patients with hypercholesterolemia and in postmenopausal women. We examined the effect of soy protein supplementation on serum lipids in a randomized, double-blinded, placebo-controlled trial. A total of 60 male and 90 female study participants aged 35 to 65 years were recruited from the community in Beijing, China. They were randomly assigned to receive 40 g isolated soy protein per day (n=76) or complex carbohydrate placebo (n=74) for 12 weeks. Fasting serum total cholesterol, HDL-cholesterol, and triglyceride were measured at baseline, and at interim (6 wks) and termination (12 wks) follow-up visits using standard methods. Overall, 92.0% (138/150) of the study participants completed the trial. The results were determined using an intention-to-treat analysis. At baseline, the supplementation and control groups were similar in age (55.8 vs. 55.9 yrs), blood pressure (135.9/82.6 vs. 134.5/82.2 mm Hg), weight (70.1 vs. 67.7 kg), total cholesterol (201.2 vs. 205.5 mg/dl), HDL-cholesterol (44.3 vs. 45.6 mg/dl), LDL-cholesterol (129.7 vs. 129.7 mg/dl), and triglyceride (135.7 vs. 151.1 mg/dl) levels. Compared to the carbohydrate control group, the soy protein supplementation group had a net increase in serum lipid of 3.3% (p=0.047) for total cholesterol, 4.7% (p=0.038) for HDL-cholesterol, 3.0% (p=0.21) for LDL-cholesterol, and 2.6% (p=0.67) for triglyceride levels. Our study suggests that soy protein intake may increase HDL-cholesterol but not affect LDL-cholesterol significantly in populations with a normal blood cholesterol level and consumption of a relatively low animal protein diet.