Forty-one RCTs were included (n=1,756) comprising of 18 crossover trials (n=421), four Latin square trials (n=66), 17 parallel trials (n=1,185) and two factorial trials (n=84). There was no evidence of publication bias.
Pooled analyses showed soy protein supplementation was associated with a significant reduction in mean total cholesterol (-5.26mg/dl, 95% CI: -7.14, -3.38), low-density lipoprotein cholesterol (-4.25 mg/dl, 95% CI: -6.00, -2.50) and triglycerides (-6.26 mg/dl, 95% CI: -9.14, -3.38) and a significant increase in high-density lipoprotein cholesterol (0.77 mg/dl, 95% CI: 0.20, 1.34).
In subgroup analyses, soy protein supplementation was associated with a reduction in total and low-density lipoprotein cholesterol levels in all subgroups, with a slightly greater effect in participants with a mean baseline total cholesterol level of less than 240mg/dl and low-density lipoprotein level of less than 160mg/dl compared to those with elevated cholesterol levels. The effect of soy protein supplementation on high-density lipoprotein cholesterol was slightly greater in participants with an elevated cholesterol at baseline (at least 240mg/dl).
The amount of soy protein and isoflavone supplementation was significantly inversely related to net changes in cholesterol, low-density lipoprotein cholesterol and triglycerides. Net change in high-density lipoprotein was positively related with amount of soy protein and isoflavones.
The sensitivity analyses showed similar results.