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Don’t Panic! Understanding the Link Between Processed Meat and Cancer

You’ve probably seen the breathless headlines today saying that eating meat gives you cancer. While it is true that eating red and processed meats has been definitively linked to an increase in certain cancers, this is no time to panic—or sell the barbecue.

The Evidence

Today, the International Agency for Research on Cancer (IARC) published findings in the journal Lancet Oncology linking the consumption of red — meat that is a deep red color before cooking, such as beef — and processed — meat that is sold preserved, like salami and hotdogs — meats to certain kinds of cancer, notably bowel cancer. (Fish and poultry meat so far have not been linked to increased cancer risks.)

According to a study in 2003, the breakdown products of heme, part of the substance that makes blood red, hemoglobin, may be to blame. When the heme in red meat is digested, it produces carcinogenic chemicals called “N-nitroso” compounds. The same compounds can form when the nitrogen-based preservatives in processed meats make their way into the gut.

The new study is the summation of over 800 studies — by looking at a large number of studies as a whole, scientists can identify larger trends or results. The strongest link is between those with the highest meat consumption and colorectal cancers. This isn’t news to the scientific community: the link between red and processed meats and cancer is now as clear as the link between smoking and cancer, according to the IARC.

The Real Risk

Putting red and processed meats in the same cancer category as smoking and asbestos is understandably scary (and invites misunderstanding, as Ed Yong points out at The Atlantic). While most people know that smoking is definitely bad for your health, the general consensus on eating meat feels closer to “probably not great, but pass me another burger.” Though we have enough evidence to say that a diet high in red and processed meat does cause cancer, the evidence also says that it doesn’t cause very many cases.

The IARC places cancer-causing agents or carcinogens into five basic categories: carcinogenic to humans (Group 1), probably carcinogenic to humans (Group 2A), possibly carcinogenic to humans (Group 2B), not classifiable as to its carcinogenicity to humans (Group 3), and finally probably not carcinogenic to humans (Group 4). Red meat has been classified in Group 2A, and processed meat in Group 1.

As you can see, these categories tell us what causes cancer or not, but not how much. In other words, something can be in the same category as cigarettes but not cause a fraction of the cancer cases cigarettes do. This is the case with red and processed meats.

MeatCancer_PIC1Image: Cancer Research UK

In an extremely informative post on the new meat classification, at Cancer Research UK features a quote from carcinogen expert Professor David Phillips that puts the findings in perspective. “To take an analogy, think of banana skins,” Phillips says, “They definitely can cause accidents, but in practice this doesn’t happen very often. And the sort of harm you can come to from slipping on a banana skin isn’t generally as severe as, say, being in a car accident.”

“But under a hazard identification system like IARC’s, ‘banana skins’ and ‘cars’ would come under the same category.”

The bottom line is that while processed meats do cause cancer like smoking does (and red meats probably do), they doe not cause nearly as many cases. According to the stats of another meta-analysis by cancer researchers in 2011, the increase in all cancer cases that come from a red and processed meat-heavy diet is three percent. Which is to say, if everyone stopped eating red and processed meats altogether, it may prevent three percent of cancer cases. If everyone stopped smoking it would prevent almost 20 percent of all cancer cases.

MeatCancer_PIC2Image: Cancer Research UK

And while smoking accounts for almost 90 percent of lung cancer cases, a heavy red and processed meat diet only accounts for 20 percent of bowel cancer cases—the cancer most linked to the meats’ consumption.

The difference here is in “absolute” and “relative” risk. The 2011 data that makes up the infographic above says that those with the biggest red and processed meat intake increase their chances of colorectal cancer (compared to those who ate the least amount of meat) by around 17 percent. That sounds scary on its own, but the risk is relative. The absolute risk of bowel cancer for those who ate the least amount of processed meat (at least in the UK) was 56 out of 1,000 people. If those people changed their diet, 66 out of 1,000 in the UK would develop colorectal cancer. Any increase is bad, but it is small when compared to something like smoking.

Another way to think about absolute and relative risk is to imagine the powerball lottery. If you buy one lottery ticket, and then decide to buy one more, you have increased your chances of winning by 100%. Sounds great, right? But if the absolute chances of winning the powerball are 1 in 175,000,000—you are 15 times more likely to get attacked by a shark—then you are increasing your chances to 2 in 175,000,000. Still not very likely.

What To Do About It

You don’t have to eliminate red and processed meats from your diet just yet: these findings are established with data from those who have the meatiest meals. If you are worried about cancer and have a very meaty diet, cutting down on the amount of meat you eat is a fine idea. You can substitute red meat for white or fish. Reduce portion sizes while adding in vegetables to round out the meal. And though no amount of cigarette smoke is a “good” amount, red meat is still a valuable source of nutrients. Just enjoy it in moderation and chances are pretty good that an occasional steak won’t do you in.

IMAGES: Featured via Braii (Barbecue) Very Well Done by Paul Saad; Infographics via Cancer Research UK

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