[intro theme]

Hank Green: Last week the International Agency For Research On Cancer released a report establishing a link between eating processed meat -which I love- and cancer; specifically, colorectal cancer. And you might have heard people say things like "eating meat is as dangerous as smoking cigarettes!" And "the World Health Organization has declared war on deliciousness!"

But both of those extreme examples are a little misleading. There is no war on deliciousness. The World Health Organization is not drafting you into an eternal conflict against the forces of bacon. It's not even telling not to eat bacon, and processed meat is not as carcinogenic as cigarettes. The IARC is the cancer agency under the umbrella of the World Health Organization, and one of their main goals is to identify stuff that causes cancer.

And now they've analyzed red meat: the muscle of a mammal like beef, or pork, or lamb, and processed meat: meat that's been treated in some way before you cook it: like sausage, or hot dogs or bacon.

The compiled the results of more than eight hundred epidemiological studies -which examine entire populations of people for patterns- taking into consideration the mechanistic evidence: the stuff that we can see happening under a microscope or in a chemical reaction.

And what they concluded is that processed meat does cause cancer. The IARC found that for every 50 grams of processed meat you eat, on average, per day, your risk of developing colorectal cancer goes up by 18%. Which does not mean that you have an 18% chance of developing that cancer. According to current statistics, if you live in America you have a 5% chance of developing colorectal cancer at some point in your lifetime. That's an average for everybody, no matter their risk factors, and if you eat 50 grams of processed meat a day, that 5% chance becomes a 5.9% chance. Because .9 is 18% of 5, it's an 18% increase to your starting cancer risk, not a flat 18% increase in your chance to develop that cancer, those are two totally different things.

So yeah, if you eat a portion of bacon for breakfast every morning, your risk of developing colorectal cancer is about 1% more than somebody who doesn't. Does that mean that you should stop eating bacon? I don't know, how much do you like it? It's up to you.

But because the IARC concluded that processed meat definitely can cause cancer, they categorized it as group 1, with all of the other definite carcinogens. The IARC's categories are there to tell you the strength of the scientific evidence saying that something can cause cancer, not how dangerous that something is.

The group one list does include stuff like cigarettes, it also includes plutonium, and wood dust, and the soot from a home chimney. Not all of those things are equally dangerous. In terms of health risk, I'll take working in a wood shop over a smoking habit any day, and processed meat is not one of the more dangerous things on that list.

Red meat, on the other hand, is categorized as group 2A: things that are probably carcinogens, but there isn't enough evidence to say for sure. While most of the evidence supported the hypothesis that red meat could also cause cancer, there were too many well-designed studies that couldn't establish a link.

So what is it about processed meat that can cause cancer? Cancer happens when the DNA in one of your cells mutates or is damaged in a way that causes it to replicate out of control. That runaway cell division forms a tumor which will keep growing even as it invades and destroys neighboring tissues.

Certain chemicals are formed in the meat during the process of processing and cooking the meat can then produce even more chemicals. These compounds are what's dangerous, because they break down in your body to form free radicals that can rip apart your DNA. Free radicals are ions that want to bonds with the organic compounds in your body - DNA is one of the things that it can bond with.

Of these, the N-nitroso compounds or NOCs are the most dangerous, they're formed when amino acids in meat are exposed to oxides of nitrogen compounds where a nitrogen atom and an oxygen atom are bonded together. This exposure happens naturally during smoking, pickling, or drying, like during smoking, the meat is exposed to the nitrogen in the smoke. And it can also happen when nitrates and nitrites are added on purpose, which many manufacturers do because those compounds prevent growth of bacteria, like the guy that causes botulism.

But those oxides of nitrogen bonded to amino acids can form these N-nitroso compounds which are massively bad for you, but super good at causing the DNA mutation that can lead to cancer. Like, for example N-nitroso dimethylamine, or NDMA, which is one of the most carcinogenic compounds on Earth. It's actually used by researchers to induce tumors in lab rats.

When your body metabolizes this stuff, NDMA breaks into nitrite and methyl radicals. The nitrite bonds with other molecules in your cells to produce formaldehyde, the stuff they used to embalm corpses, until they stopped doing that because it caused cancer. And the methyl radicals can do a lot of things - most of them bad - but they particularly like to form bonds with guanine, which is one of the base molecules of your DNA. When they do, they rip guanine out of its bonds with the other bases, producing new, potentially cancerous errors.

So, can eating processed meat lead to cancer? Yes. Should you stop eating it? I mean, if you're eating like pounds of hot dogs every day, yeah, you might want to cut back, but the new report doesn't make any recommendations, that's not what it's for. The World Health Organization puts out these reports just to keep people informed. Which is also our goal, so I hope that you are more informed now. This way, you can understand what the risk is and decide for yourself whether it's worth it.

Thank you for watching this episode of SciShow news and thanks especially to all of our patrons on Patreon who make this show possible. If you want to help us out and help us keep making videos like this, Patreon.com/SciShow is the place to go, and if you just want to keep getting smarter with us, you can go to YouTube.com/SciShow and subscribe.

[endscreen]