Recently, the International Agency for Research on Cancer (IARC), a part of the World Health Organization (WHO), has classified processed meat (e.g. hot dogs, ham, sausages, corned beef, beef jerky, canned meat & meat-based preparations and sauces) as carcinogenic to humans (Group 1); and red meat (all mammalian muscle meat e.g. beef, veal, pork, lamb, mutton, horse and goat) as probably carcinogenic to humans (Group 2A). The food we eat daily suddenly becomes “toxic” and consumers are scared by the classification instantly.
Image Source: BBC, 2015
Although some stakeholders do not agree with the conclusion made by the IARC that meat is carcinogenic or probably carcinogenic, there’s no doubt that some carcinogenic chemicals may form during meat processing and cooking.
1. N-nitroso compounds
Nitrate is commonly added in cured meats to inhibit toxin formation by Clostridium botulinum bacteria. When nitrate combines with amines or amides in food, carcinogenic N-nitroso compounds (e.g. nitrosamines) are formed. Nitrosamines have been shown to be carcinogenic in experimental animals and epidemiologically implicated carcinogenicity.
2. Polycyclic Aromatic Hydrocarbons
High temperature food processing (e.g. roasting & grilling), smoking or cooking food will generate a huge amount of polycyclic aromatic hydrocarbons (PAHs), especially in charred foods.
Some PAHs can bind DNA inside cell. This in turn affects gene expression and may finally lead to cancer development. For example, benzo[a]pyrene, the most toxic PAH, is classified by IARC as Group 1 agent whereas three other PAHs (cyclopenta[c,d]pyrene, dibenzo[a,l]pyrene & dibenz[a,h]anthracene）are classified as Group 2A agent.
Apart from PAHs, high-temperature cooking (e.g. barbecuing / grilling, broiling or pan-frying) will also generate heterocyclic amines (HCAs) in cooked muscle meat.
Some HCAs are genotoxic. For example, 2-amino-3-methylimidzo[4,5-f]quinoline, is classified as a probable human carcinogen (Group 2A) whereas nine other HCAs are considered as possible human carcinogens (Group 2B).
Should We Stop Eating Meat?
It is impossible to completely avoid eating foods that might contain carcinogens (zero intake from daily diet). This is because carcinogens are somehow present in many commonly consumed foods other than processed meat e.g. arsenic in rice, aflatoxins in cereal and their products、acrylamide in deep fried food (e.g. fried potatoes、bakery products).
In this connection, we should reasonably treat the “carcinogenic meat” issue, and there’s no need for undue concern. As long as processed meat and/or red meat are not “over-consumed”, adverse health consequences to the human body will not occur. We should not ignore nutritional aspects of meat, even though consuming in moderation of foods that contain carcinogens is definitely correct. In fact, WHO also states that eating meat has known health benefits.
The key question to ask is therefore “risk” of eating meat. WHO estimated that every 50 gram portion of processed meat eaten daily increases the risk of colorectal cancer by about 18%. However, the data available for evaluation did not permit a conclusion about how much meat it is safe to eat.
“The dose makes the poison” is an adage in toxicology. Any substance beneficial for health (e.g. pharmaceutical drug) can turn into toxic if the consumption amount is too much (e.g. overdose of pharmaceutical drug is equivalent to eating poison). Therefore, food safety authority should advise people the “safe level of intake” of processed meat and/or red meat, without leading to illnesses.
Apart from limiting the intake of meats, practices in processing and cooking meats should also be improved to reduce the formation of carcinogens, so as to minimize dietary exposure to carcinogens. For example, maximum levels are set for nitrate use in cured meats with consideration of minimum level to achieve the desired effect; and optimization of cooking temperature & time to avoid overcooking.