Red meats, processed meats and colorectal cancer. Central role of heme iron and of catalysis of lipid peroxidation. Towards nutritional prevention?

The International Agency for Research on Cancer (IARC) classified in October 2015, the consumption of red meats as probably carcinogenic (Group 2A) and consumption of processed meats as carcinogenic in humans (Group 1). This ranking is primarily based on epidemiological studies with meta-analyses that demonstrate a convincing positive association between consumption of both these meat products and the risk of colon cancer. Experimental studies have identified the mechanisms involved. Several hypotheses, found in the literature, involve lipids, proteins, heterocyclic amines (HCA) and polycyclic hydrocarbons from cooking with high-temperature, N-nitroso compounds (NOCs) and heme iron. Although human studies have excluded hypotheses with proteins and lipids, recent experimental studies have demonstrated the central role of heme iron without additives or a synergistic effect of the HCA and NOC; role of heme iron confirmed in humans on the E3N cohort. This promoting effect of heme iron is explained by its ability to induce a strong luminal lipid peroxidation leading to the formation of cytotoxic and genotoxic alkenals. The identification of the role of peroxidation opens the door to nutritional prevention by adding antioxidants in the diet or directly in meat products.