I’m sure you’ve seen the rash of fear-mongering headlines proclaiming red meat to be as carcinogenic as smoking. In fact, I know so because dozens of you have asked me for my thoughts. What’s going on? Do we need to worry? What actually happened? Why have your vegan friends become even more smug than before? Why did your crazy aunt send an email in all caps pleading for you to stop eating “so much beef”?
Let’s look at what the WHO actually meant. When they analyze a substance’s cancer-causing potential, the WHO places it into one of three categories:
Group 1, for “established carcinogens”—things like smoking, asbestos, nuclear bomb blasts, and, now, processed meat.
Group 2A, for “probable carcinogens”—your glyphosates, your UV radiation, your grass-fed lamb leg.
Group 2B, for “possible carcinogens”—judging from the list, almost everything qualifies here.
Whether something ends up in Group 1, 2A, or 2B depends only on the strength of the evidence, not the degree of risk. If a compound has been confirmed beyond doubt to increase breast cancer risk by 2%, it goes in Group 1. If a compound has a reasonable but not overwhelming amount of evidence suggesting that it increases breast cancer risk by 25%, it goes in Group 2A. The second compound is likely more dangerous and confers greater risk than the first compound.
Okay, so what is the actual degree of risk? In the paper, each additional intake of 100 grams (about a quarter pound) of red meat was associated with a 17% increase in colorectal cancer risk. 17%’s a big number. It’s almost 20%, which is basically 25%. Then you’re halfway to a 50% increase, and it only gets worse from there.
But that’s a relative risk. Though it’s the third most common cancer (and cause of cancer-related deaths), the absolute risk of developing colorectal cancer, even in old age when the risk is at its highest, isn’t exactly high. For the average 50 year old, his or her lifetime risk of colorectal cancer is 1.8%. If that 50 year old has a relative with colon cancer, the risk is 3.4%. Having two relatives with a history of colon cancer pushes it up to 6.9%. On the big scale of things that can kill you, colorectal cancer isn’t even in the top five.
Don’t get me wrong: colorectal cancer is deadly. Particularly if you have familial history of colorectal cancer, you should do your best to avoid it. It’s not a pleasant cancer. It’s just that the relative risk increase of 17% doesn’t amount to nearly as much absolute risk.
In addition, the epidemiology portion of the paper is based on data drawn from food frequency questionnaires (FFQ). FFQs require people to recall their typical diet over the last year. Here’s a sample FFQ (PDF); see how you do trying to recall the last 12 months. Suffice it to say, they aren’t very reliable. People lie. People forget. People tell you what they think you want to hear. FFQs are probably the best option available for assessing, but they aren’t good enough.
There’s also the fact that red meat suffers from an “unhealthy user bias.” Most heavy red meat eaters aren’t sprinting, lifting weights, and going for walks every day. They’re eating their meat between buns, and with fries. They’re getting their red meat from Burger King or the 7-11. They can try to control for most of these associations, but it’s impossible to account for everything.
Mechanisms for Carcinogenicity
That’s not to say the paper relies entirely on epidemiological research based on food questionnaires. They do propose a few mechanisms for meat-related carcinogenicity.
One is the formation of nitrosamines in the gut after consumption of nitrate-cured meats and red meat. Cured meats, like bacon and sausage, contain ample nitrosamine precursors and have been shown to create the carcinogenic metabolites when consumed. The iron in red meat also acts as a nitrosamine precursor.
Another is the formation of carcinogenic compounds during the processing, er, process. Polycyclic aromatic hydrocarbons and n-nitroso-compounds form during smoking and curing, respectively. Both are carcinogenic.
The last is the formation of carcinogenic compounds during high-heat cooking of meat. Grilling, sautéing, searing, and caramelization of red meat all have the potential to create heterocyclic amines and, over open flame, polycyclic aromatic hydrocarbons. The higher the temp and longer the application, the more carcinogenic the resulting meat. Well-done meat is more carcinogenic than rare-cooked meat, for example.
On one hand, these are definite carcinogens. The linked summary paper contains some strong references, and I’ve written about these very same compounds in previous posts.
On the other hand, the carcinogenic potential of red meat is mitigated by certain cooking and marinating techniques, and the risk can also be modified and even eliminated by the addition or subtraction of different foods to the rest of the diet. What are these?
Marinating your red meat using herbs, spices, garlic, onions, citrus, vinegar, wine, and even honey before high-heat cooking can reduce the formation of carcinogens.
Cooking in liquid. Simmer, braise, pressure-cook, slow-cook, steam—these “gentler” cooking methods reduce carcinogen formation. Doubly so if you incorporate some of the mentioned marinade ingredients into the process.
Eating green vegetableslike broccoli with your meat can reduce the carcinogenicity of red meat-related compounds.
Eating prebiotic fibers and resistant starch. In the original summary paper, they reference a study as evidence of red meat consumption causing colon cancer. Human volunteers who consumed 300 grams of cooked red meat each day showed evidence of pre-cancer metabolites in their poop. But the real finding was that adding 40 grams of prebiotic fiber to the 300 grams of red meat each day prevented the formation of those colorectal cancer indicators. The fiber used was a maize powder high in resistant starch. Any source of resistant starch should work—cold potatoes, potato starch, green bananas.
Could grass-fed/pasture-raised meat eliminate or reverse the association? Maybe. For one, pastured meat contains conjugated linoleic acid (CLA), a healthy trans-fat with anti-cancer effects. Two, pastured animal fat tends to be naturally imbued with antioxidants from all the greenery the animals consume; this protects the fat from oxidation, and certain antioxidants found in pastured animal fat, like lutein, are even associated with lower risks of colon cancer in humans and actively reduce colon cancer in animal trials. But many of the proposed mechanisms for carcinogenicity apply equally to grass-fed red meat. I wouldn’t hang my hat on that one.
I would hang my hat on the following suggestions, however.
Don’t live off bacon, hot dogs, and salami.
The more red meat you eat, the more vegetation you should be eating. Make sure some of that vegetation contains prebiotic fiber, especially resistant starch. Maybe all that plant matter is unnecessary if you maintain a perfect carnivorous diet, but why risk it? Besides, plants are delicious.
If you’re gonna sear or grill something over high heat, which is completely and utterly delicious and thus necessary from time to time, consider using a marinade—especially if you cook this way frequently.
Mark Sisson is the founder of Mark’s Daily Apple, godfather to the Primal food and lifestyle movement, and the New York Times bestselling author of The Keto Reset Diet. His latest book is Keto for Life, where he discusses how he combines the keto diet with a Primal lifestyle for optimal health and longevity. Mark is the author of numerous other books as well, including The Primal Blueprint, which was credited with turbocharging the growth of the primal/paleo movement back in 2009. After spending three decades researching and educating folks on why food is the key component to achieving and maintaining optimal wellness, Mark launched Primal Kitchen, a real-food company that creates Primal/paleo, keto, and Whole30-friendly kitchen staples.