Regular consumption of red meat is thought to increase the risk of colorectal cancer. However, the link between red meat and disease is controversial because red meat is a group of foods and the causative factor could therefore be only part of that group. Processed meats for example are thought to cause cancers in the gastrointestinal system because they contain nitrites and nitrates that can be converted to carcinogenic nitrosamines under conditions present in the human gut. The association between red meat and cancer can therefore be biased by the inclusion of processed meats. In addition, red meat is not all the same. Quality varies depending on the source of the meat and this too can have an influence on the association with cancer. For example conventionally farmed animals are fed hormones and other drugs that can increase growth rates, but may also accelerate cell proliferation in humans, thus increasing the risk of cancer in those eating contaminated meat. grass fed and organic meat on the other hand may not alter risk.
Therefore studies that have investigated the association between red meat and cancer but not analysed individual meat components and their individual effects do not accurately represent the true picture. To address this problem, one recent study analysed the associations between red meat sub-types and colorectal cancer using data from the Danish Diet, Cancer and Health cohort study which included 53, 988 subjects1. During the 13.4 year follow up, 644 cases of colon cancer and 345 cases of rectal cancer were reported from medical records. When they analysed the results the researchers found that total red meat intake did not correlate with the risk of cancer. There was also no evidence of an association between consumption of poultry and gastrointestinal cancers. However, the risk of cancer did correlate with the sub-types of meat and the origin of that meat. In particular, the risk of colon cancer was significantly elevated with regular consumption of veal and lamb, and the risk of rectal cancer was significantly elevated with regular consumption of pork.
However, beef was inversely associated with the risk for rectal cancer. When the authors investigated the protective factors that may decrease the risk of cancers associated with meat they found that substituting fish for lamb, but not pork or veal, significantly lowered the risk of cancer. However, the lower risk of colon cancer in those with high fish intakes was only present if the subjects had a low fruit fibre intake, with higher fruit fibre intakes ameliorating the protective effect of fish. Those with a low fibre intake of less than 8 grams per day had a 13 % increase in colon cancer for each 25 gram incremental increase in processed meats, supporting other studies that have shown protective effects of fibre on colon cancer. However, dietary fibre from either fruit fibre or cereal fibre did not affect the association between red meat, processed meat, fish or poultry and rectal cancer. Substituting poultry for lamb also lowered the risk of cancer. These results suggest that only sub-groups of red meat increase cancer risk and other factors modify this risk.