*2.4.1 Mechanism*

The carcinogenic compounds that form during processing include NOCs and PAHs. NOCs are exogenously introduced from nitrates and nitrites added during the preservation process [25, 27] but can also be formed endogenously. In processed meat, HI is nitrosylated because curing salt contains nitrate or nitrite. There is evidence that nitrosylated HI promotes carcinogenesis at doses that are five to six times lower than non-nitrosylated HI [25].

However, it is likely that a combination of mechanisms contribute to a higher risk of developing CRC among those who consume high quantities of processed meat. Similar to red meat, processed meat is high in fat, protein, and HI, which can promote carcinogenesis through the mechanisms described under red meat [25, 26]. In addition, processed meats such as sausages are often cooked at high temperatures, leading to increased exposure to HAAs and PAHs [25, 27], with levels varying according to meat type, temperature, cooking time, and method [25]. The invariably higher fat content of processed meat when compared to red meat may stimulate carcinogenesis through synthesis of secondary bile acids. However, human data supporting this hypothesis are weak [27].
