Red meat and cancer

Red meat, including beef, pork, lamb, and veal, is classified by IARC as Group 2A (probably carcinogenic to humans), primarily based on its association with colorectal cancer (CRC). The association is most consistent for high amounts of unprocessed red meat consumed over time. Some evidence also links red meat consumption to gastric cancer and possibly to other digestive tract cancers, though these associations are less established than the CRC link.

Several mechanisms have been proposed to explain how red meat may promote colorectal carcinogenesis. Haem iron in red meat catalyses the formation of N-nitroso compounds (NOCs) in the gut and generates reactive oxygen species that can damage colonic epithelium. High-temperature cooking of red meat produces heterocyclic amines (HCAs) such as PhIP and MeIQx, as well as polycyclic aromatic hydrocarbons (PAHs) like benzo[a]pyrene, both of which form mutagenic DNA adducts when metabolically activated in colonic tissue. HCA-DNA adducts have been measured in human colon tissue and correlate with red and processed meat intake in case-control studies. A recently identified mechanism involves alkylating DNA damage from red meat components contributing to a specific SBS87 mutational signature identified in colorectal cancers, providing a molecular footprint of meat-induced mutagenesis. Diets high in red meat also tend to be low in dietary fibre, removing the counterbalancing protective effects of short-chain fatty acids such as butyrate.

A meta-analysis of studies examining meat consumption and CRC risk found significant associations for both red and processed meat, with the effect size for processed meat generally larger than for unprocessed red meat. GBD 2021 analyses identified high red meat intake among dietary risk factors contributing to CRC mortality and disability-adjusted life years (DALYs) globally, with the effect most prominent in older adults. An analysis of CRC burden in China found high red meat intake contributed to CRC burden over 1990 to 2021, though its relative contribution declined compared to other lifestyle factors. A global analysis of diet-attributable cancers projected that the burden from red meat consumption would continue rising to 2050 if dietary patterns remain unchanged. Mendelian randomisation analyses have examined relationships between dietary patterns including meat intake and specific cancers including gastric cancer, finding suggestive but inconclusive causal associations beyond the colorectal cancer evidence.

People who consume large quantities of red meat daily, particularly cooked at high temperatures such as grilling or barbecuing, face the greatest risk. Adults aged 65 and over with high red meat intake show an elevated CRC burden in global analyses. Men, who on average consume more red meat than women, may face somewhat higher risk from this dietary pattern. Individuals with a diet otherwise low in fibre and protective vegetables alongside high red meat consumption may face compounded risk. Genetic variants affecting carcinogen metabolism, such as N-acetyltransferase and cytochrome P450 polymorphisms relevant to HCA activation, may modify individual susceptibility to meat-induced DNA damage.

The IARC Group 2A classification reflects probable rather than definitive carcinogenicity, based on consistent but not fully conclusive epidemiological evidence and a credible mechanistic basis. Evidence is largely observational, with confounding as a significant challenge: red meat consumers often differ from non-consumers in other dietary and lifestyle ways that are difficult to fully separate. The consistency of findings across multiple large cohort studies and the mechanistic plausibility of proposed pathways together support a likely causal relationship for CRC, but absolute risk increases per portion are modest.

Studies suggest that high consumption of red meat is probably associated with increased colorectal cancer risk, with a dose-dependent relationship. The absolute effect per serving is smaller than that seen for processed meat. The quality of the evidence points toward high-temperature cooking methods and high quantities as the most concerning patterns, while moderate consumption with diverse preparation methods appears to carry lower risk.