Editor's Note: Large European and American studies are the most recent to examine the link between red meat and cancer. Medscape talked to the study authors and reviewed other evidence to determine whether there is reason to have a beef about eating beef.
Red Meat and Colorectal Cancer
The preponderance of data gathered in recent decades has supported a link between colorectal cancer (CRC) and red meat consumption, especially processed (cured) red meat (hot dogs, bologna, sausages, bacon, ham, lunch meats). A dose-response relationship was demonstrated by Chan and colleagues, who reported that the risk for CRC increased by 21% for every 50 g/day of processed red meat intake and by 29% for every 100 g/day consumed.
Biologic plausibility for this relationship has been proposed and potential mechanisms of carcinogenesis examined. Pro-cancer factors in red meat might be excess fat, protein, or iron, or heat-induced mutagens. Red meat contains high levels of heme iron (the "red" in red meat), which has a catalytic effect on the endogenous formation of carcinogenic N-nitroso compounds and on the formation of cytotoxic and genotoxic aldehydes by lipoperoxidation. Processed meats contain nitrites and sodium. Cooking meat at high temperatures or on an open flame produces heterocyclic amines (HCAs) and polycyclic aromatic hydrocarbons (PAHs), which are potent carcinogens. Despite numerous investigations, to date none of these hypotheses have been able to convincingly explain the link between red meat intake and cancer risk. For example, in a study that demonstrated a dose-dependent effect of red meat intake on colon cancer, the etiologically relevant compound in cooked meat was thought to be HCAs. However, grilled and fried chicken contain much higher levels of HCAs than beef, but the intake of poultry is not related to cancer risk.
The investigation into the role of red meat consumption in cancer of the colon has extended to cancer precursors and to cancers at different colorectal subsites. A meta-analysis found high ingestion of red and processed meat to be positively associated with increased risk for colorectal adenoma.[6,7] The population-based Norwegian Women and Cancer cohort examined associations of meat intake with incident cancer at different subsites within the colon in 84,538 women, finding that high processed red meat intake (especially sausages) was associated with increased risk for cancer of the proximal colon, distal colon, and rectum.
Researchers were looking not only at the link between red meat and cancer, but also at the mechanisms that would explain such a link, because saturated fat was no longer believed to be sufficiently explanatory. Genetic polymorphisms that might increase susceptibility to CRC through gene-environment interactions have been the subject of study. Because products of high-temperature meat cooking, including PAHs and HCAs, require metabolic activation to exert carcinogenesis, it was believed that metabolizing isoenzymes such as N-acetyltransferase 1 (NAT1) and 2 (NAT2) might modify risk for CRC. Findings have been variable. Shin and colleagues suggest that genetic polymorphisms involved in the metabolic activation of HCAs may indeed modify the risk for colorectal polyps, a possible precursor to cancer.
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Cite this: Red Meat and Cancer: What's the Beef? - Medscape - Jun 20, 2013.