Bacon, sausages, and other processed meats are now classified as Group 1 carcinogens according to an announcement made by the World Health Organization on 26 October 2015. The organisation also mentioned red meat as a likely cause of cancer. These conclusions came from the review study of a scientific panel that examined 800 epidemiological studies from the United States, Europe, Japan, Australia, and elsewhere.
The International Agency for Research on Cancer of WHO invited 22 scientists to assess the association between the consumption of red meat and processed means and more than 16 types of cancer.
Based on the review and analysis of scientific literature, the researchers concluded that there is sufficient evidence linking the consumption of processed meat with the development of colorectal cancer. The WHO said that colorectal cancer is the second most lethal form of cancer in the U.S. with death tolls amounting to nearly 50,000 per year.
Red meat also carries a slightly lower albeit substantial risk. Apart from colorectal cancer, red meat consumption has been positively associated with pancreatic cancer and prostate cancer.
The review also cited a 2011 study by Doris S. M. Chan et al that involved a meta-analysis of 28 studies on meat consumption and cancer risk dating back to 1996. The analysis found that risk for developing colorectal cancer jumps by 18 percent for every 50 grams or 1.7 ounces of processed meat consumed each day. The risks involving daily consumption of red meat is 17 percent for every 100 grams.
Another study involving rodents and human tissue revealed the consumption of red and processed meats increases the production of chemical compounds, including N-nitroso-compounds—known for causing oxidative damage to intestinal tissue.
Curing meat leads to elevated levels of NOCs and other carcinogenic compounds known as polycyclic aromatic hydrocarbons. Heating meat leads to the formation of heterocyclic aromatic amines, a known mutagen and cancer-causing agent. The review study puts emphasis on the fact that exposing these meats to high-temperature through pan-frying or grilling results in the highest levels of these chemicals.
The International Agency for Research on Cancer of WHO maintains a list of compounds or activities with suspected, probable, and definitive links to cancer, with each possible item falling into a designated grouping based on whether or not it causes cancer.
Processed meats are now classified as Group 1 carcinogens alongside tobacco smoking, exposure to asbestos, and the most dangerous variant of the human papillomavirus. Red meats are classified as Group 2A carcinogens alongside inorganic lead, DDT, and vinyl fluoride, among others. A Group 1 classification means that a compound or activity definitely leads to the development of cancer depending on exposure levels while a Group 2A classification means a mere probability for a compound or activity to cause cancer.
Further details of the WHO scientific panel study are in the article “Carcinogenicity of consumption of red and processed meat” published in 2015 in the journal The Lancet Oncology. More details of the study of Chan et al are in the article “Red and processed meat and colorectal cancer incidence: Meta-analysis of prospective studies” published in 2011 in the journal PLOS One. The list of suspected, probable, and definitive carcinogenic compounds or activities maintained by the International Agency for Research on Cancer of WHO can be accessed on this website.