Dietary patterns and colorectal cancer: systematic review and meta-analysis

Studies on the association between single foods or nutrients and colorectal cancer have provided inconsistent results. Previous reviews did not conduct a quantitative synthesis of the relation with dietary patterns. We conducted a systematic review and meta-analysis of studies addressing the association between dietary patterns and colorectal cancer. Studies quantifying the association between dietary patterns (defined a posteriori) and colorectal cancer were identified in PubMed (until 01.08.2010) and through backward and forward citation tracking (ISI Web of Science and Scopus). Summary relative risk (RR) estimates and 95% confidence intervals (95% CI) were computed for highest versus lowest levels of exposure, for colon cancer (CC) and rectal cancer (RC), and for proximal and distal CC, by random effects meta-analysis. Heterogeneity was quantified using the I² statistic. Eight cohort and eight case–control studies defining patterns through principal components and factor analyses were included in the systematic review. Meta-analyses were conducted for three patterns: (i) ‘drinker,’ characterized by high alcohol consumption (CC: RRcombined = 0.96, 95% CI: 0.82–1.12, I² = 0.6%; RC: RRcombined = 0.83, 95% CI: 0.47–1.45, I² = 65.1%); (ii) ‘healthy,’ characterized by high fruit/vegetables consumption (CC: RRcombined = 0.80, 95% CI: 0.70–0.90, I² = 55.1%; RC: RRcombined = 1.02, 95% CI: 0.89–1.17, I² = 10.8%); (iii) ‘western,’ characterized by high red/processed meat consumption (CC: RRcombined = 1.29, 95% CI: 1.13–1.48, I² = 31.7%; RC: RRcombined = 1.13, 95% CI: 0.92–1.39, I² = 40.6%). Summary estimates for proximal and distal CC were similar. The risk of CC was increased with patterns characterized by high intake of red and processed meat and decreased with those labelled as ‘healthy.’ No significant associations were observed for RC.