Systematic review, meta-analysis and regression of randomised controlled trials reporting an association between an intake of circa 25 g soya protein per day and blood cholesterol

Aims To determine the effect of a daily intake of circa 25 g soya protein on blood lipids in adults with normal or mildly elevated cholesterolaemia. Methods Medline and other scientific databases were searched to identify randomised controlled trials (RCTs); these were systematically reviewed against pre-determined criteria. Eligible RCTs evaluated the effect of 25 g (range 15–40 g) soya protein on measures of blood lipids. Results from RCTs were pooled using standard meta-analysis methods. Results Thirty studies containing 42 treatment arms (n = 2913), with an average soya protein intake of 26.9 g met the inclusion criteria. Soya protein inclusion led to reductions in standard difference in mean low density lipoprotein (LDL), total cholesterol and blood triglycerides of 0.23 mmol/L (95% confidence interval (CI) −0.160 to −0.306, p < 0.0001), 0.22 mmol/L (95% CI −0.142 to −0.291, p < 0.0001) and 0.08 mmol/L (95% CI −0.004 to −0.158, p = 0.04), respectively. There was no effect on mean difference in apolipoprotein A (ApoA), but ApoB was reduced by 0.021 g/L (p = 0.01) in the soya group. Meta-regression analysis indicated no dose response relationship between soya protein intake in the range of 15–40 g and standard difference in LDL or HDL. All data were tested for heterogeneity and none identified. Conclusions The inclusion of modest amounts soya protein (ca. 25 g) into the diet of adults with normal or mild hypercholesterolaemia resulted in small, highly significant reductions in total and LDL cholesterol, equivalent to ca. 6% LDL reduction. This practically achievable intake, particularly when combined with other dietary measures, can make a useful contribution to blood cholesterol management.