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

Current evidence indicates that red and processed meat intake increases the risk of colorectal cancer; however, the association with colorectal adenomas is unclear. 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. 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. 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. These results indicate an elevated risk of colorectal adenomas with intake of red and processed meat, but further prospective studies are warranted.