A Meta-Analysis of Randomized Controlled Trials of the Effects of Soy Intake on Inflammatory Markers in Postmenopausal Women

Background: Elevated concentrations of serum inflammatory cytokines, specifically TNF-alpha and IL-6, as well as C-reactive protein (CRP), are commonly observed after menopause. Objectives: Because soy isoflavones may have some anti-inflammatory potential, the aim of the present systematic review and meta-analysis of randomized controlled trials (RCTs) was to explore whether soy intake affects serum markers of inflammation in postmenopausal women. Methods: PubMed, Web of Science, and the Cochrane Library were systematically searched up to August 2020. All RCTs that met the following criteria were included: 1) studies of the effects of soy intake on inflammatory markers; 2) any date of publication; 3) conducted on postmenopausal women; 4) with sufficient quantitative data for meta-analysis. Effect sizes were expressed as weighted mean differences (WMDs) and 95% Cls. A total of 24 RCTs assessing the effects of soy intake on serum concentrations of CRP TNF-alpha, and IL-6 were included in the analysis. A random-effects model was used to determine the overall effect. Results: Soy supplementation significantly reduced CRP by 0.11 mg/L in postmenopausal women (95% CI: -0.22, -0.004 mg/L; P= 0.0414), but did not affect IL-6 or TNF-a. Significant reductions in CRP concentration occurred when natural soy products were given (WMD: -0.23 mg/L; 95% CI: -0.29, -0.17 mg/L; P < 0.001). This is equivalent to a similar to 9% reduction in CRP concentration from baseline. Conclusions: Although our meta-analysis found evidence that soy products significantly reduce CRP concentrations in postmenopausal women, the mechanisms by which soy foods and their constituents affect inflammatory biomarkers still need to be clarified.