The past few days have been a media frenzy over the International Agency on Cancer Research (IARC), a subsidiary of the World Health Organization (WHO), concluding that processed meats cause cancer. When I first saw the headlines, I thought, “Duh. We’ve known this. How is this new information?” With the gaining traction, I sought out information from my dietitian colleagues. And I thought, if I needed a little help making sense of all this, maybe you did, too. So let’s break it down together.
The Players and History
IARC is a research group. Their job is to understand the research pertaining to cancer. Then organizations like WHO and the USDA turn the information into recommendations and guidelines (think: 2015 Dietary Guidelines).
IARC put together a panel of 22 experts from 10 countries to evaluate over 800 studies on red and processed meats to help us better understand what research can tell us about their relationship to cancer.
WHO has been recommending that we avoid processed meat and limit red meat intake for years. So has the American Institute for Cancer Research. So have many dietitians and health professionals.
MANY studies have shown a relationship between certain cancers (especially colorectal, stomach and pancreatic) and processed and red meats. But correlation is not causation*. Additional research and evaluation of the research was truly needed to say that the meat causes cancer.
*To highlight this point, I heard someone say that wearing a size extra-large is highly correlated to obesity. But we can all agree that if a normal-sized person started wearing extra-large clothing, it would not - on its own - cause them to become obese!
What the Report Said
The report was intended to evaluate the strength of evidence that links these meats to cancer. Was the research done well, what kind of studies were done, how many are there, were confounding factors accounted for, etc.
According to the IARC Q&A, processed meats are defined as “[meats that have been] transformed through salting, curing, fermentation, smoking, or other processes to enhance flavor or improve preservation. Most processed meats contain pork or beef, but [not all].”
So while this includes the obvious meats like hotdogs, bacon and beef jerky, it also includes some of the less obvious ones like deli meat and poultry sausages. The evidence was very strong associating carcinogenicity and processed meat. So strong that the IARC puts processed meats into Group 1: Carcinogenic to Humans (for colorectal cancer).
The IARC Q&A defines red meat as “all types of mammalian muscle meat, such as beef, veal, pork, lamb, and goat.” The evidence was moderately strong associating carcinogenicity and red meat, which means that IARC puts it into Group 2A: Probably Carcinogenic to Humans.
This report also looks at the size of the risk.
The dose makes the poison, right? So how much processed meat does it take until it’s carcinogenic? An analysis of data from 10 studies estimates that for every 50-gram portion (about 2-ounce) of processed meat eaten daily, there is an 18% increase in risk of colorectal cancer.
In the United States, the average person's risk for developing colorectal cancer in their lifetime is about 4.5% according to the National Cancer Institute of the NIH. An additional 18% risk from 2 ounces per day of processed meats per day puts that risk at 5.3% over their lifetime. This is still a very small risk. We hear that our risk jumps by almost 20%, and it sounds really scary. This number is clinically significant, but doesn't have the intense real-world significance.
From a worldwide perspective, according to the Global Burden of Disease Project, about 34,000 cancer deaths per year are attributable to diets high in processed meat. Contrast that with the 1 million cancer deaths globally due to tobacco smoking. The fact that both processed meats and smoking are in IARC’s Group 1 does not mean that they have equal impact on your cancer risk. The way that most of the media worded their articles seemed to equate eating bacon with smoking. That is either sensationalized journalism, or a journalist who didn't understand the report.
What Does This Mean?
Keeping your processed meat in check is still worth it, especially if you have other risk factors for cancers (like family history, a sedentary lifestyle and/or obesity). But it’s not reason to freak out and never eat bacon again. Or to become a vegetarian.
”These findings further support current public health recommendations to limit intake of meat,” says Dr Christopher Wild, Director of IARC. “At the same time, red meat has nutritional value. Therefore, these results are important in enabling governments and international regulatory agencies to conduct risk assessments, in order to balance the risks and benefits of eating red meat and processed meat and to provide the best possible dietary recommendations.”
As Dr. Wild said above, red meat contains lots of valuable nutrients – specifically high-quality protein, B vitamins, iron and zinc. But too much of anything is a bad thing. Also, we don’t know what it is about the meat that causes the increased cancer risk. In fact, it might not be the meat itself, but rather how it’s cooked or processed.
For instance, curing and smoking can form carcinogenic chemicals, like N-nitroso-compounds (NOC) and polycyclic aromatic hydrocarbons (PAH). Cooking can produce PAHs and heterocyclic aromatic amines (HAA). These compounds are produced in high temperature cooking, or when the food is in direct contact with a flame. Think of grilling or pan-frying, here. We don't know how much of a factor this played in the research the IARC evaluted, because there weren't enough studies that differentiated among cooking method.
So… What Should I Do?
First, take a deep breath. I'm not saying never eat bacon or a steak. I don't even think that's what the recommendations are saying.
But do take this opportunity to look at your diet. How much processed or red meat do you eat? How often? The answer should not be every day, and it shouldn’t be a 72-ounce steak. Stick to portions of 2 ounces of processed meats and 3-4 ounces of red meat (that’s a ¼-pound burger).
Consider varying your protein sources. Including dairy, poultry, eggs and seafood are other ways to get high-quality proteins into your diet. Don’t forget about plant-based protein, as well: peas, legumes, beans, lentils, nuts and seeds.
Amp up your vegetable intake. Part of the reason that processed and red meats are associated with cancers is likely due to a lower fruit and vegetable intake. Don’t forget that nutrition is about more than just individual components - it's about your diet as a whole. Research continues to show us a correlation between fruit and vegetable intake and lower rates of cancer.
To paraphrase research by Katz and Meller, a diet of minimally processed foods (mostly plants) is associated with both health promotion and disease prevention. These tenets work whether you’re following a vegan, Paleo, or Mediterranean diet. Our public health crisis isn’t due to a lack of knowledge, but due to our failure to take what we know and put it into practice.
Thanks to all the RDs who responded on Facebook and through listservs who helped compile this list. Just in case you can't get enough on this subject :)