Systematic review of the prospective cohort studies on meat consumption and colorectal cancer risk: a meta-analytical approach.

The relation between meat consumption and colorectal cancer risk remains controversial. In this report, we quantitatively reviewed the prospective observational studies that have analyzed the relation between meat consumption and colorectal cancer. We conducted electronic searches of MEDLINE, EMBASE, and CANCERLIT databases through to the end of June 1999 and manual searches of references from retrieved articles. We used both fixed and random-effects meta-analytical techniques to estimate the overall association and to investigate possible sources of heterogeneity among studies. Thirteen studies were eligible for inclusion in the meta-analysis. Pooled results indicate that a daily increase of 100 g of all meat or red meat is associated with a significant 12-17% increased risk of colorectal cancer. The marginally significant between-study heterogeneity for all meat and red meat was explained by a number of study-level covariates. A significant 49% increased risk was found for a daily increase of 25 g of processed meat. The individual study estimates for processed meat showed no detectable heterogeneity. On the basis of this quantitative review of prospective studies, the overall association between meat consumption and risk of colorectal cancer appears to be positive, with marginal heterogeneity between studies. The finding for processed meat and data from experimental studies suggests that it may also be an important predictor of colorectal cancer risk. However, because only a few of the studies reviewed here attempted to examine the independent effect of meat intake on colorectal cancer risk, the possibility that the overall association may be confounded or modified by other factors cannot be excluded.