Red and processed meat intake and risk of colorectal adenomas: a systematic review and meta-analysis of epidemiological studies

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BACKGROUND: Current evidence indicates that red and processed meat intake increases the risk of colorectal cancer; however, the association with colorectal adenomas is unclear. OBJECTIVE: To conduct a systematic review and meta-analysis of epidemiological studies of red and processed meat intake and risk of colorectal adenomas as part of the Continuous Update Project of the World Cancer Research Fund. DESIGN: PubMed and several other databases were searched for relevant studies from their inception up to 31 December 2011. Summary relative risks (RRs) were estimated using a random effects model. RESULTS: Nineteen case-control studies and seven prospective studies were included in the analyses. The summary RR per 100 g/day of red meat was 1.27 (95 % CI 1.16-1.40, I (2) = 5 %, n = 16) for all studies combined, 1.20 (95 % CI 1.06-1.36, I (2) = 0 %, n = 6) for prospective studies, and 1.34 (95 % CI 1.12-1.59, I (2) = 31 %, n = 10) for case-control studies. The summary RR per 50 g/day of processed meat intake was 1.29 (95 % CI 1.10-1.53, I (2) = 27 %, n = 10) for all studies combined, 1.45 (95 % CI 1.10-1.90, I (2) = 0 %, n = 2) for prospective studies, and 1.23 (95 % CI 0.99-1.52, I (2) = 37 %, n = 8) for case-control studies. There was evidence of a nonlinear association between red meat (p nonlinearity < 0.001) and processed meat (p nonlinearity = 0.01) intake and colorectal adenoma risk. CONCLUSION: These results indicate an elevated risk of colorectal adenomas with intake of red and processed meat, but further prospective studies are warranted.