As of today, the World Health Organisation has officially classified processed meat as "carcinogenic", alongside such notorious substances as tobacco, arsenic, and pesticides. The decision was made by the International Agency of Research into Cancer (IARC), based on a review of 800 studies from around the world that found "sufficient evidence in humans that the consumption of processed meat causes colorectal cancer".
At the same time, red meat has been classified as "probably carcinogenic", because while a direct link between it and cancer has yet to be found in humans, studies have found strong evidence for it in lab animals. So what does this mean for everyone who isn't vegetarian right now?
Long story short, yes these classifications are serious and based on real science; no you don't have to give up bacon, sausages, beef, or any other kind of meat in an effort to avoid a higher risk of cancer. Here's why.
First off, when we talk about processed meats, we're talking anything that has been salted, cured, fermented, or smoked, which means hot dogs, sausages, bacon, ham, corned beef, dried meat such as beef jerky, and canned meat or meat-based sauces. Red meat, on the other hand, is classified as any mammalian muscle meat, so beef, veal, venison, and pork.
According to the IARC review, for every 50 grams (1.8 ounces) of meat eaten on a daily basis - so two rashers of bacon a day - the average risk of developing colon cancer is 18 percent higher. As Joshua A. Krisch explains at Vocativ, right now, your lifetime risk of colorectal cancer is about five percent. This means that if you eat 50 grams of processed meat every day, your risk for colorectal cancer increases by 18 percent of five percent - so your total risk is 5.9 percent.
Next, we need to understand the classification system used by the IARC, which is the cancer-focussed arm of the WHO. Their job is to classify everything according to five possible categories: Group 1 is established carcinogens, Group 2A is "probably carcinogenic", Group 2B is "possibly carcinogenic", Group 3 is for things that cannot be classified, due to a lack of data, and Group 4 is "probably not carcinogenic". Group 4 includes just one entry: caprolactam, a substance used to make synthetic fibres such as the nylon in your yoga pants and brush bristles.
Two things about these groups. As Ed Yong points out at The Atlantic, the language used here, e.g. "probably" and "possibly", is fairly ambiguous, and not particularly helpful. But most importantly, while it's easy to interpret the things in these categories as equal, they in no way impart the same risk of cancer as each other. For example, smoking tobacco and eating processed meat are both Group 1 carcinogens, but they do not give you the same risk of cancer. Not even close.
As this Cancer Research UK infographic illustrates, the risk of getting lung cancer if you smoke is extremely high. Studies have found that out of the 44,488 new cases of lung cancer in the UK in 2012, 86 percent of them were caused by tobacco. On top of that, research has shown that 19 percent of all types of cancers are caused by smoking. Add all that up, and if you got rid of smoking, you'd have 64,500 fewer cases of cancer in the UK every year.
By that same logic, if we got rid of processed meat, just 8,800 cases of cancer would be prevented in the UK every year. Both smoking and processed meat have been directly linked to cancer, but that doesn't mean the level of risk is equal. "The classifications reflect how strong the base of evidence is," David Wallinga, senior health officer for the US Natural Resources Defense Council, told Kaleigh Rogers at Motherboard. "It doesn't say anything about how strong of a carcinogen that particular thing is. It's not saying eating hot dogs is as potent at causing cancer as being exposed to asbestos."
So don't believe the headlines that try to get you to make that kind of connection in your head, such as this one from The Guardian earlier today: "Processed meats rank alongside smoking as cancer causes - WHO."
With that in mind, what makes processed meat definitely carcinogenic? The exact cause is not yet clear, but here's what the IARC report says:
"Meat consists of multiple components, such as haem iron. Meat can also contain chemicals that form during meat processing or cooking. For instance, carcinogenic chemicals that form during meat processing include N-nitroso compounds and polycyclic aromatic hydrocarbons.
Cooking of red meat or processed meat also produces heterocyclic aromatic amines as well as other chemicals including polycyclic aromatic hydrocarbons, which are also found in other foods and in air pollution. Some of these chemicals are known or suspected carcinogens, but despite this knowledge, it is not yet fully understood how cancer risk is increased by red meat or processed meat."
While the jury is still out on the actual reason why processed meats and possibly red meat are linked to higher instances of bowel cancer, we certainly shouldn't just sit around and be complacent until scientists can figure it out. But that doesn't mean we should panic either. The key here is the amount of processed meat you're eating.
So if you're eating two rashers of bacon every single day of your life, or a ham sandwich every lunchtime, if you're not comfortable with the fact that you're definitely increasing your chances of getting cancer, you need to cut back. A sausage sandwich or bacon and egg roll here and there isn't going to cause you much dramas, but you shouldn't be eating them more often than that anyway, as Ottawa-based physician, Yoni Freedhoff, pointed out to Motherboard: "I didn't think it was news that hot dogs aren't good for you." A good trick is to just swap some of that processed and red meat with less questionable - but still delicious - proteins, such as chicken, turkey, and fish.
In light of everything, the advice from experts is pretty much what it's always been: for god's sake, just eat healthy. "Our advice on diet stays the same: eat plenty of fibre, fruit and vegetables; cut back on red and processed meat, and salt; and limit your alcohol intake. It might sound boring but it's true: healthy living is all about moderation," says Casey Dunlop at Cancer Research UK. "Except for smoking: that's always bad for you."
You can read the entire study at The Lancet.