Red meat includes beef, veal, lamb, pork, and mutton.1 Processed meat is treated with a cure and/or is smoked, and may have chemical additives to prolong its shelf life and/or enhance flavor; these meats include sausage, bacon, ham, and some deli meats. Though red meat contains important nutrients such as essential amino acids, vitamin B12, iron, and zinc, it is associated with an increased risk of some cancers in epidemiologic studies.2

Colorectal Cancer

Several meta-analyses of observational studies demonstrated an increased risk of colorectal cancer (CRC) with higher red meat intake. In a meta-analysis of 27 prospective cohort studies, the overall summary of relative risk estimate (SRRE) indicated a significant increase in CRC risk with higher red meat consumption compared with lower intakes (SRRE, 1.11; 95% CI, 1.03-1.19), but heterogeneity was high (P-H = .014).3 Fresh red meat consumption alone (ie, not processed meats), however, did not increase the risk of CRC (SRRE, 1.05; 95% CI, 0.98-1.12), with lower heterogeneity (P-H = .328).

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A more recent meta-analysis, which included 111 cohort studies, found a 12% increase in CRC risk for each 100 g of red and processed meat consumed per day (relative risk [RR], 1.12; 95% CI, 1.04-1.21; I2 = 70%).4 When only red meat was analyzed, the significance was marginal (RR, 1.12; 95% CI, 1.00-1.25; I2 = 24%). Red meat consumption was associated with colon (RR, 1.22; 95% CI, 1.06-1.39; I2 = 12%), but not rectal cancer (RR, 1.13; 95% CI, 0.96-1.34; I2 = 0%).

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Another study, which stratified the analysis by meat subtype, demonstrated that higher beef consumption was associated with an increased risk of CRC and colon cancer, but not rectal cancer, compared with lower beef consumption.5 Higher lamb intake was also associated with an increased risk of CRC; colon and rectal cancer were not, however, evaluated in the studies included in this analysis. High pork intake was not associated with an increased risk of CRC, colon, or rectal cancers.

Findings were similar in a meta-analysis of a Japanese population, in which 6 cohort studies and 13 case-control studies were evaluated. Higher red meat intake was significantly associated with an increased risk of CRC (RR, 1.16; 95% CI, 1.001-1.34) and colon cancer (RR, 1.21; 1.03-1.43).6

Another study pooled data from the Nurses’ Health Study and Health Professionals Follow-up Study and stratified the data by tumor location.7 Red meat intake was not associated with an increased risk of distal or proximal colon cancer, but 1 serving of processed red meat per day significantly increased the risk of CRC (hazard ratio [HR], 1.15; 95% CI, 1.01-1.32; P = .03) and distal colon cancer (HR, 1.36; 95% CI, 1.09-1.69; P = .006).