Evidence linking red meat consumption to disease is controversial because studies have been inconsistent in their findings. For example, while some studies show an association between high intakes of red meat and cancer, other studies show no such association. The inconsistent results of epidemiological studies are likely down to the confounding variables, such as the degree of processing of the meat and the amount of cooking. Meat cooked by pan frying and grilling for example, can result in the formation of carcinogenic compounds such as heterocyclic amines (HCAs) and polycyclic aromatic hydrocarbons (PCHs). Consumption of processed meats can result in the formation of N-nitroso compounds (NOCs) which can be synthesised endogenously from the nitrite and nitrate used to preserve cooked meats. The association between meat and cancer could therefore be dependent on its processing, and this may explain the inconsistent results from epidemiological results.
Because of the possibility that factors associated with red meat consumption may increase the risk of cancer, researchers1 have investigated the association of red meat intake with renal cell carcinoma (RCC) in a cohort of 492,186 healthy subjects between 50 and 71 years. A dietary assessment and the intakes of haem iron, HCAs, NOCs, PAHs, nitrite and nitrate in cooked and processed meats were calculated. Comparison of the fifth quintile of intake for red meat (62.7g per 1000kcal) to the first quintile (9.8g per 1000kcal) was associated with a significant increase in papillary RCC, but only a trend towards an increased risk for RCC. However, intakes of the HCA 2-amino-1-methyl-6-phenyl-imidazol[4,5-b]pyridine and the PAH marker benzo(a)pyrene were associated with a 20-30% increase risk of RCC and a 2-fold increase in the risk of papillary RCC.
These results suggest that the association between red meat and RCC is not strong. The reason for this is likely that there are confounding variables, namely the presence of certain carcinogenic substances that are present in some red meat. This would explain the inconsistent results seen with epidemiological studies investigating the association between red meat consumption and cancer. These carcinogenic metabolites are processed through the kidneys during metabolism and excretion and this is the likely reason that they may increase the risk of renal cancers. Interestingly, most of the detrimental effects represented by significant associations in this study were limited to subjects in the top 20% (fifth quintile) with most of the study population consuming a relatively small amount of the carcinogenic compounds present in red meat. This may further explain the inability of previous studies to find significant associations between red meat and cancer.
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