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

Abstract

ABSTRACT Background Elevated concentrations of serum inflammatory cytokines, specifically TNF-α 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% CIs. A total of 24 RCTs assessing the effects of soy intake on serum concentrations of CRP, TNF-α, 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-α. 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 ∼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. This systematic review was registered at www.crd.york.ac.uk/prospero/ as CRD42020179232.