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IARC Working Group on the Evaluation of Carcinogenic Risks to Humans. Red Meat and Processed Meat. Lyon (FR): International Agency for Research on Cancer; 2018. (IARC Monographs on the Evaluation of Carcinogenic Risks to Humans, No. 114.)
4.1. Digestion and metabolism
The composition of red meat and processed meat, as well as their potential contaminants, is described in detail in Section 1 of this Monograph. Red meat and processed meat are sources of high-quality protein, fat in highly variable amounts, and a range of micronutrients.
A diet high in red meat or processed meat may contain high levels of fat. The digestion of food lipids consists of a series of enzyme-catalysed steps resulting in absorbable components, whereby the release of bile from the gallbladder is essential. It has been suggested that dietary fat promotes the development of cancer of the colorectum (Boyle et al., 1985; Reddy, 1992). Several mechanisms have been postulated to explain this association, including the stimulating effect of high-fat intake on the secretion of secondary bile acids in the gut; this proposed mechanism has received the most attention. These bile acids may promote tumour formation by acting as aggressive surfactants on the mucosa, thus increasing cell loss and proliferation (Bruce, 1987; Owen, 1997; Bernstein et al., 2005). Other proposed mechanisms for the promoting role of dietary fat include an increase in the amount of free fatty acids in the colonic lumen, which may damage the colonic epithelium and induce cell proliferation, and an augmented risk for obesity (Calle & Kaaks, 2004). Dietary fat intake is also associated with peroxidation of unsaturated fatty acids (see Section 4.5.2).