Processed meat is considered to be any meat that has been modified in order to either improve its taste or to extend its shelf life. Methods of meat processing include salting, curing, fermentation, smoking, boiling, frying, and/or the addition of chemical preservatives.^[1] Processed meat is usually composed of pork or beef or, less frequently, poultry. It can also contain offal or meat by-products such as blood. Processed meat products include bacon, ham, sausages, salami, corned beef, jerky, hot dogs, lunch meat, canned meat, chicken nuggets,^[2] and meat-based sauces. Meat processing includes all the processes that change fresh meat with the exception of simple mechanical processes such as cutting, grinding or mixing.^[3]

Meat processing began as soon as people realized that cooking and salting prolongs the life of fresh meat. It is not known when this took place; however, the process of salting and sun-drying was recorded in Ancient Egypt, while using ice and snow is credited to early Romans, and canning was developed by Nicolas Appert who in 1810 received a prize for his invention from the French government.^[3]

Preservatives

Nitrate and sodium nitrite found in processed meats can be converted by the human body into nitrosamines that can be carcinogenic, causing mutation in the colorectal cell line, thereby causing tumorigenesis and eventually leading to cancer.^[4] Processed meat is more carcinogenic compared to unprocessed red meat because of the abundance of potent nitrosyl-heme molecules that form N-nitroso compounds.^[5]

A principal concern about sodium nitrite is Nitrosation/nitrosylation, the formation of carcinogenic nitroso-compounds in meats containing sodium nitrite or potassium nitrate,^[6] especially nitrosyl-haem (nitrosyl heme).^[7] In addition to nitrosyl-haem, carcinogenic nitrosamines can be formed from the reaction of nitrite with secondary amines under acidic conditions (such as occurs in the human stomach) as well as during the curing process used to preserve meats.^{[citation needed]}

Nitrate and nitrite are consumed from plant foods as well as animal foods, with 80% of a typical person's nitrate consumption coming from vegetables, especially leafy and root vegetables such as spinach and beets.^[8] Some nitrate is converted to nitrite in the human body.^[8] Nitrate and nitrite are classified as generally recognized as safe (GRAS) by the U.S. Food and Drug Administration, and are not directly carcinogenic. Yet, when nitrate or nitrite interact with certain components in meat, such as heme iron, amines, and amides, they can form nitroso compounds, which may contribute to the association between consumption of processed meats and higher incidence of colorectal cancer.^[9]

Health effects

The International Agency for Research on Cancer (IARC) at the World Health Organization (WHO) classifies processed meat as Group 1 (carcinogenic to humans), because the IARC has found sufficient evidence that consumption of processed meat by humans causes colorectal cancer.^[10][11][12]

A 2016 report by the American Institute for Cancer Research and the World Cancer Research Fund found that processed meat consumption also increases the risk of stomach cancer.^[13]

In 2020, the American Cancer Society stated that "it is not known if there is a safe level of consumption for either red or processed meats. In the absence of such knowledge, while recognizing that the amount of increased risk isn’t certain, the ACS recommends choosing protein foods such as fish, poultry, and beans more often than red meat, and for people who eat processed meat products to do so sparingly, if at all."^[14]

Several recent reviews have found that processed meat consumption is associated with an increased risk of cardiovascular disease, gastric cancer and stroke.^[15][16][17]