According to the Canadian Cancer Society, "the evidence is convincing that eating processed meat increases the risk of colorectal cancer. The reasons why eating processed meat increases the risk of colorectal cancer are currently being studied.."
The Canadian Cancer Society notes that one of the possible reasons for this link is the presence of nitrites. "Nitrites and nitrates are not cancer-causing by themselves, but in certain conditions in the body they can be changed into by-products called N-nitroso compounds, such as nitrosamines and nitrosamides. N-nitroso compounds are associated with an increased risk of cancer."
The society also recommends that people "save processed meat for special occasions, such as ham for a holiday dinner or a hot dog at a sporting event," noting that "An increased intake of red and processed meat appears to modestly increase the risk of death from cancer, heart disease and other diseases."
Marketplace contacted the Canadian Cancer Society for our original story and confirmed that this position would also apply to "natural" processed meats currently on the market.
Similarly, the American Cancer Society and the Public Health Agency of Canada recommend reducing intake of processed meat as much as possible to reduce cancer risk.
The World Cancer Research Fund and the American Institute for Cancer Research looked at all the existing evidence in their report "Food, Nutrition, Physical Activity and Prevention of Cancer":
The report states that: "There is a substantial amount of evidence, with a dose response relationship apparent from cohort studies. There is strong evidence for plausible mechanisms operating in humans. Processed meat is a convincing cause of colorectal cancer."
The researchers also expressed concern, specifically, about the role that nitrites might play in this link. "There is concern that nitrite, from processed meats for example, nitrates in vegetables, and preformed nitrosamines may be involved in carcinogenesis, particularly in the stomach... Dietary nitrates and nitrites are probable human carcinogens because they are converted in the body to N-nitroso compounds."
The report concludes that people should eat little or no processed meat. Read the full report.
Given the body of research linking processed meat consumption and an increase in cancer risk, the US-based Physicians Committee for Responsible Medicine has been lobbying to have processed meat removed from school lunches in the US. You can find out more about this campaign at cancerproject.org/.