Nitrates are added as preservatives to processed meats. Nitrates can be readily reduced to form nitrites, which in turn can interact with dietary substrates such as amines and amides to produce N-nitroso compounds (NOCs): nitrosamines and nitrosamides, which are known mutagens and carcinogens. Nitrates or nitrites are used in smoked, salted, and pickled foods. Sodium and potassium nitrates are present in a variety of foods and give hot dogs and processed deli meats their pink color, but the main dietary sources are vegetables and drinking water.
There are different types of nitrosamines, and many can increase the risk for cancer. Nitrosamines are some of the main carcinogens in tobacco smoke, for example Bacon, hot dogs, and processed meat can contain high levels of both sodium nitrite. They’re also high in protein, which is made up of amino acids. On exposure to high heat, this combination creates the perfect conditions for nitrosamines to form. Cooking vegetables, however, is less likely to produce nitrosamines. People rarely cook vegetables at very high heat, and they don’t contain large amounts of protein.
NOCs are also produced endogenously in the stomach and colon of people who eat large amounts of red meat. Studies looking at the detrimental effects of smoked foods have not demonstrated a clear, consistent connection between these foods and stomach cancer.
Charring or cooking meat at high temperatures over an open flame (400° F or more) can cause the formation of polycyclic aromatic hydrocarbons (PAHs) and heterocyclic amines (HCAs). PAHs have shown clear indications of mutagenicity and carcinogenicity.
Normal roasting or frying food does not produce large amounts of PAHs compared with the amount produced when cooking over open flames. Animal proteins that produce the greatest dripping of fat on to the flames register the highest PAH formation. For example, grilled beef produces larger amounts of PAHs than grilled chicken, which produces higher amounts than oven-grilled chicken. The source of the flame can also influence PAH production; charcoal grilling promotes the most, followed by flame gas, and finally oven grilling.
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