Does total antioxidant capacity affect the features of metabolic syndrome? A systematic review

Purpose There is some evidence that suggest a higher dietary total antioxidant capacity (DTAC) is associated with a lower risk of metabolic syndrome (MetS). Considering the conflicting results in this field, this paper aims to provide a comprehensive summary of studies on the association of DTAC and components of MetS. Design/methodology/approach A systematic review of articles indexed in PubMed, Scopus and Google Scholar, published from inception to September 2018, with defined keywords, was done. Duplicate or irrelevant reports were screened out and data were extracted through critical analysis. Finally, among the 353 articles, 19 articles met the inclusion criteria. Findings The included cohort studies revealed that higher DTAC was associated with reduced risk of MetS. Also, the association between DTAC and mortality risk of MetS was insignificant in these studies. The case-control studies showed high DTAC is inversely associated with MetS, its components and complications. The randomized controlled trials found that changes in DTAC were negatively correlated with oxidized low-density lipoprotein cholesterol and there was a positive association between DTAC and subjects' weight and body mass index. Finally, results from the cross-sectional studies were inconsistence in this regard. Originality/value The assessed relationship between MetS or its components with DTAC is inconsistent in the included studies. Different sample size, dietary assessment tools, DTAC index values and geographical location may justify the observed inconsistencies. It seems that further studies are needed to reveal more confident and reliable findings.