In controlled dietary intervention studies, intake of red meat, but not white meat, has been shown to increase
endogenous formation of NOCs in a dose-responsemanner.
It has been suggested that this effect is mediated by heme iron, which is highly abundant in red meat.
Although all red meat contains heme iron, there are species variations: the highest amounts have been reported in beef and lamb and lower levels in pork and veal.
Thus, if the potential carcinogenic effect of red meat in driven by heme iron, the risk might vary according to red meat subtype.
Individual associations between specific red meat subtypes (e.g., beef and pork) and risks for colon and rectal cancer have, however, been evaluated in only 3 previous prospective studies, which gave conflicting results.