It may have come as a surprise to the approximately 60% of Americans who consume red or processed meat that the International Agency for Research on Cancer (IARC), a part of the World Health Organization, recently reported that processed meat is a carcinogen, and red meat is probably a carcinogen to humans.2
This report was based on a review of the world’s body of human and laboratory research by an international working group of experts convened for the IARC Monographs Programme. Since 1971, the IARC Monographs Programme has specifically sought to evaluate the potential carcinogenic effects of a range of exposures – from specific chemicals, complex chemical mixtures, and occupational exposures to physical and biological agents – and lifestyle factors, including dietary factors.
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Because of the growing evidence on the potential carcinogenic effects of processed meat and red meat intake, it was not surprising that in 2014, an IARC advisory committee recommended the evaluation of processed and red meat.
While the new report has generated considerable media attention, and many questions about whether or not it is safe to consume processed meat (for example, hot dogs, bacon, sausage, deli meats, etc.) and red meat (e.g., mammalian muscle meat such as beef, pork, and lamb), the working group’s conclusions were not unexpected.
Based on review of earlier studies, the American Cancer Society first recommended limiting consumption of red and processed meat in 20023 and has maintained this recommendation in its latest (2012) Guidelines on Nutrition and Physical Activity for Cancer Prevention.4
The conclusions also are consistent with the World Cancer Research Fund (WCRF)/American Institute for Cancer Research (AICR) Continuous Update Project,5 which found the evidence “convincing” that diets high in red meat and processed meat are associated with increased risk of colorectal cancer.5 Moreover, the IARC conclusions support the United States 2015 Dietary Guidelines for Americans Advisory Committee’s recommendation to consume a healthful dietary pattern that is “lower in red and processed meat.”6
The classifications for both red and processed meats are based primarily on evidence showing an increased risk of colorectal cancer, the third most commonly diagnosed cancer among men and among women in the United States.
In the IARC report, it was noted that a meta-analysis of 10 prospective studies showed a statistically significant 18% (95% confidence interval, 1.10-1.28) increased risk of colorectal cancer per 50 g (about 1.75 ounces) per day of processed meat consumption, and a 17% (95% CI, 1.05-1.31) increased risk of colorectal cancer per 100 g (about 3.5 ounces) per day of red meat.7
In terms of lifetime risk, this means that eating an extra 50 g of processed meat per day would be expected to increase the average person’s risk of ever developing colorectal cancer from about 5% to about 6%. A similar excess risk would be observed for 100 g of red meat consumption.
While this increased risk is modest, for heavy meat eaters and for those at high risk of colorectal cancer, limiting processed and red meat consumption is one way to help reduce their risk of colorectal cancer.
Some mechanisms thought to be responsible include consumption of N-nitroso compounds formed during meat processing, and the endogenous formation of N-nitroso compounds in the gut, which can be catalyzed by heme iron in red meat. High-heat cooking methods such as pan frying or barbecuing produce high concentrations of known or suspected carcinogens, including heterocyclic amines and polycyclic aromatic hydrocarbons.8,9
The data for other cancers are more limited, but positive associations were also seen for processed meat consumption and stomach cancer, and for red meat and cancers of the pancreas and prostate (advanced prostate cancer in particular).2
It is worth keeping in mind that preventing smoking initiation and improving smoking cessation rates remain the most important ways to reduce cancer mortality rates worldwide. In addition, there is considerable evidence that other healthful lifestyle habits also are important for minimizing cancer risk, including limiting alcohol consumption, maintaining a healthy body weight throughout adulthood, being physically active, and consuming a mostly plant-based diet.
Our own research,10 using data from the Cancer Prevention Study II and that of others,11,12 has shown that a lifestyle most consistent with following the American Cancer Society’s Guidelines on Nutrition and Physical Activity for Cancer Prevention13 has marked impact on reducing the risk of developing many types of cancer, as well as dying from cancer, cardiovascular disease, and all causes.
In terms of meat consumption, the American Cancer Society’s guidelines emphasize choosing fish, poultry, or beans as alternatives to processed and red meat. For those who choose to eat red meat, selecting lean cuts and eating smaller portions are recommended.4 The guidelines also recommend preparing meat, poultry, and fish by baking, broiling, or poaching, rather than frying or charbroiling, to reduce the formation of carcinogens during the cooking process.