A role for milk proteins in cancer prevention

Evidence from animal and cell culture studies suggests that milk proteins, especially those associated with whey, have anti-carcinogenic properties. These properties appear to be related to components rich in the sulphur amino acids cysteine and methionine and containing the gamma-glutamyl-cysteine residue which makes cysteine readily bioavailable for synthesis of glutathione, a strong xenobiotic deactivating and anti-neoplastic agent. Methionine, which can also be utilised for glutathione synthesis in times of cysteine deficiency, is also important as a methyl donor. Hypomethylation of DNA is an important risk factor for cancel at a number of sites. The provision of glutathione precursors by whey proteins may, at least in part, explain the ability of dietary whey protein to enhance both humoral and cell-mediated immune responses in laboratory animals. The whey protein fraction contains a number of high-affinity binding proteins that bind iron, folic acid, vitamin B12, riboflavin, retinol and vitamin D. Binding of iron by lactoferrin may make this potential pro-carcinogen unavailable for intestinal damage, whereas the vitamin D. binding proteins make their vitamins (potential anti-cancer agents) more bioavailable and protect them from utilisation by intestinal micro-organisms. Whey also contains growth factors (transforming growth factor-beta and basic fibroblast growth factor) and an inhibitor (mammary-derived growth inhibitor) with anti-cancer action at extremely low concentrations. These compounds may survive digestion in sufficient quantities to generate a physiological response. The anticancer properties of the membrane phospholipid sphingomyelin, a strong tumour suppressor lipid, associated with whey protein concentrate and skim milk powder, and the calcium content of the products, should be taken into consideration when assessing the role of milk proteins in cancer prevention.