Dietary Total Antioxidant Capacity and Risk of Gastrointestinal Cancers: A Systematic Review and Meta-analysis of Observational Studies

Background: Gastrointestinal (GI) cancers are common types of cancers. Among different factors that affect the etiology of GI cancers, diet has an important contribution. Dietary antioxidants decrease oxidative stress which plays a pivotal role in carcinogenesis. Several studies assessed the relation between dietary total antioxidant capacity (TAC) and risk of GI cancers. Dietary TAC was measured by three indices including FRAP (ferric ion reducing antioxidant power), TRAP (total radical-trapping antioxidant parameter), and TEAC (trolox equivalent antioxidant capacity). We performed a systematic review and meta-analysis of published studies to determine the association between dietary TAC and GI cancers risk. Methods: Eligible studies were selected from PubMed, ISI Web of Science and Scopus databases from inception until May 2018. Case-control and cohort studies that reported GI cancer risk estimates for dietary TAC were included. We ignored the distinction between case-control and cohort studies. We applied random-effects to estimate pooled relative risks. Subgroup analysis was done based on study design. Results: Among the seven observational studies that were included, four were cohort studies and three were case-control studies. Dietary FRAP, TRAP, and TEAC reduced GI cancer risk: FRAP; 0.71; 95% CI: 0.58–0.85, TRAP; 0.65; 95% CI: 0.57–0.75, TEAC; 0.70; 95% CI: 0.59–0.83, respectively. Conclusion: This study indicated that dietary TAC significantly decreased the risk of GI cancers. Nevertheless, further prospective studies are required to clarify the association between dietary TAC and risk of GI cancers.