Theresa Hastert, Ph.D.
Last fall the International Agency for Research on Cancer (IARC) made headlines by classifying processed meat, such as bacon, sausage, and many lunch meats, as a “Group 1” carcinogen, the same classification given to cigarettes (https://duckduckgo.com/?q=iarc+processed+meat+cancer&t=ffsb). The same report found that unprocessed red meat probably causes cancer. But what do these labels mean, and should we all stop eating bacon?
IARC is a specialized cancer research agency within the World Health Organization that evaluates existing research related to potential causes of cancer. For this report they reviewed more than 800 previous studies that looked at whether eating red or processed meat was associated with cancer risk. They rated the quality of the studies by looking at the study design used, how diet information was collected, how many people were included, and whether they accounted for other factors that could affect the study results. Although they looked at studies of red and processed meat and all kinds of cancer, the largest number of studies focused on colorectal cancer.
Based on this review of previous research, IARC determined that there is a small “dose-response” relationship between processed meat and cancer, meaning that as processed meat consumption increases, so does cancer risk. They found that colon cancer was 18% higher with each additional 50 grams of processed meat (approximately 2 slices of bacon) eaten per day, so compared with people who don’t eat bacon, colon cancer risk is 18% higher in those who eat 2 slices per day, 36% higher for people eating 4 slices per day, and so on. The link was about half as strong for red meat, with colorectal cancer risk increasing by 17% for every 100 grams (3.5 ounces) eaten per day.
Research on the health effects of eating meat on cancer survivors is much more limited. There is some evidence that higher red and processed meat intake before diagnosis is associated with higher mortality from all causes, including cardiovascular disease, after being diagnosed with colorectal cancer. (http://www.jco.ascopubs.org/content/early/2013/06/25/JCO.2013.49.1126.abstract) But recent studies suggest that eating red and processed meat after diagnosis does not affect colorectal cancer survival. (http://ajcn.nutrition.org/content/103/1/192.abstract and http://www.jco.ascopubs.org/content/early/2013/06/25/JCO.2013.49.1126.abstract)
To put things in perspective, approximately 1 in 20 Americans (5%) will be diagnosed with colon or rectal cancer in their lifetime (ACS Colorectal Cancer Facts & Figures 2014-2016 http://www.cancer.org/acs/groups/content/documents/document/acspc-042280.pdf), and raising that risk by 20% would bring lifetime risk to 6%. Eating red and processed meat does not mean any one person will get colorectal cancer, but for anyone interested in reducing their risk, cutting back on red and processed meat is one way to go.
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