Thirty randomised crossover or parallel studies (n=2,913; 42 treatment arms) were included in the review. Sample sizes ranged from 22 to 216 participants. The average Jadad score was 3.5; six studies scored 5 and 10 scored 4. Seventeen studies were double blinded; two were single blinded.
Soya protein significantly reduced low density lipoprotein cholesterol (SMD -0.23 mmol/L, 95% CI: -0.160 to -0.306, p<0.0001; 42 treatment arms, four studies showed a statistically significant difference). This translated into around a 12% reduction in risk. High density lipoprotein cholesterol was not effected significantly.
Soya protein also significantly reduced blood triglycerides (SMD -0.08mmol/L, 95% CI: -0.004 to -0158, p=0.04; 39 treatment arms, only one study showed statistically significant differences) and total cholesterol (SMD -0.22 mmol/L, 95% CI: -0.142 to -0.291, p<0.0001; 41 treatment arms, five trials showed a statistically significant difference).
There was no evidence of heterogeneity for any of the analyses.
Subgroup analyses showed no significant relationships between soya protein intake (range of 15g to 40g) and low or high density lipoprotein. Further subgroup analyses and secondary outcomes were reported in the review.
There was no evidence of publication bias using funnel plots.