The World Health Organization (WHO) recently released the International Agency for Research on Cancer’s (IARC) report(PDF) classifying processed meat as “carcinogenic to humans” and red meat as “probably carcinogenic to humans.” The topic appeared all over the media and raised more questions than answers. This post is intended to help LSO readers understand the report’s 
implications.
An understanding of the IARC is important to digesting the news. The IARC Monographs review published studies and determine if evidence is strong enough to support the identification of factors (such as chemicals) as cancer-causing. The IARC divides researched factors into groups that identify an agent as…
- “Group 1: Carcinogenic to humans,”
- “Group 2A: Probably carcinogenic”
- “Group 2B: Possibly carcinogenic,”
- “Group 3: Not classifiable,” or
- “Group 4: Probably not carcinogenic.”
The IARC reviewed over 800 studies(PDF) analyzing the risk of cancer from red and processed meat. Roughly half of the reviewed studies observing cancer and red meat intake in humans found an association between red-meat consumption and colorectal cancer (cancer in the colon or rectum). The majority of studies observing cancer and processed meat intake found a positive association between processed meat consumption and colorectal canc
er. The analysis showed(PDF) that for every 50 grams of processed meat eaten per day, the risk of colorectal cancer increased by 18%.
From these findings, The IARC classified(PDF) red meat in Group 2A and processed meat in Group 1. Red meat = unprocessed muscle meat from mammals like beef, pork, and lamb. Processed meat= ANY type of meat that has been altered through salting, curing, smoking, or fermentation. Examples of processed meat include sausage links, bacon, chicken nuggets, hot dogs, and many cold cuts/lunch meat (click here for a list(PDF) of processed meats).
Processed meat was placed in the same cancer risk group as smoking–a known cause of cancer; while, red meat was placed in a group representing a likely cause of cancer. Red meat was identified as a probable cause because the associations between colorectal cancer and meat intake were inconsistent across studies. On the other hand, the link between colorectal cancer and processed meat was highly consistent.
Why would processed meat cause cancer? This is still being answered. Much of the evidence relies on studies observing groups of people and comparing meat consumption habits of those who develop cancer and those who don’t. These studies are useful but don’t provide an understanding of what causes colorectal cancer. Studies involving mice have provided possible causal explanations. These possible explanations include 4 ideas:
- High fat consumption promotes the secretion of bile acids which may play a part in promoting colon tumors
- Cooking meat at high temperatures causes the formation of Heterocyclic Amines and Polyciclic Aromatic Hydrocarbons which are carcinogenic
- Nitrites and their associated compounds are present in many processed meats and may contribute to cancer formation
- Heme (found in animal muscles and blood cells) may contribute to the formation of cancer in conjunction with Nitrites
What does this mean for you? While the IARC has identified processed meat as a known carcinogen–like cigarette smoke– this does NOT mean they bear equal cancer risks. WHO estimates that there are 34,000 global cancer deaths per year caused by processed meat. In contrast, 1,000,000 global cancer deaths per year are caused by smoking. USDA Guidelines currently recommend most adult women and men consume 5oz and 6oz of protein foods (including meat daily). Because meat still provides valuable nutrients, The WHO calls for limited intake of processed meats to reduce risk 
of colorectal cancer.
Since the 2010 National Dietary Guidelines already call for limited intake of red and processed meats as a means to lower our fat and calorie intake, this new finding simply adds further reason to follow the guidelines that already exists: Now is the time to search for healthier meat alternatives, such as fish, non-processed chicken, etc. and to save our “bacon-sausage sandwich” for an occasional treat.
For more easy-to-understand information on the link between colorectal cancer and red or processed meat, visit the WHO Q&A webpage.
Stay Tuned: On January 4th, we’ll publish another blog post on easy ways to reduce and replace processed meat in your diet as part of your 2016 New Year Resolutions!
