Red Meat & Cancer—Again! Will It Ever Stop?

Red Meat & Cancer—Again! Will It Ever Stop?

by Chris Kresser

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The media and blogosphere are abuzz with the latest report from the WHO, which classified cured and processed meats as carcinogens and put them in the same category as asbestos, alcohol, arsenic, and tobacco. But what does the research really tell us about the link between red meat and cancer?

Well, here we go again. Each year, like clockwork, the conventional medical establishment mounts an attack against red meat.

For decades, we were told not to eat it because of the cholesterol and saturated fat it contains. When that argument became less convincing, a new one was offered: we shouldn’t eat red meat because it increases production of a compound called TMAO, which causes heart attacks.

Now we’re being told not to eat red meat—and especially cured and processed meat—because it will give us cancer. In a recent report, the World Health Organization (WHO) ranked bacon, sausage, and other cured and processed meats as “group 1 carcinogens,” which puts them in the same category as tobacco, asbestos, alcohol, and arsenic. It also placed fresh red meat in the “group 2A” category, which suggests that it is “probably carcinogenic” to humans.

Of course, this isn’t a new argument; it’s been around for at least 40 years. As far back as 1975, scientists speculated that the consumption of animal products was linked to cancer. (1)

How Strong Is the Evidence Linking Red Meat to Cancer?

However, the evidence supporting this claim has never been as strong as its proponents suggest. I have critically reviewed this evidence on several occasions in the past, as have many of my colleagues. Here’s a list of a few articles and podcasts I recommend reading and/or listening to if you’d like to go deep on this topic:

I realize that many of you don’t have the time to sift through all of that material, so I’ll do my best to summarize the salient points here.

Is eating bacon the same as smoking cigarettes when it comes to cancer?

Let’s start with a critical review of the evidence linking red meat to cancer that was published in one of the most prestigious scientific journals in the world (Obesity Reviews) in 2010. (2) The authors looked at 35 studies that claimed to find an association between red meat and cancer and found numerous problems. Here are some key passages from this paper, with my commentary.

Collectively, associations between red meat consumption and colorectal cancer are generally weak in magnitude, with most relative risks below 1.50 and not statistically significant, and there is a lack of a clear dose–response trend.

Translation: the association between red meat and cancer is not strong (i.e. comparing bacon to cigarettes is absurd), and in fact is often not distinguishable from chance. If red meat really did cause cancer, you’d expect to see a linear (continuous) increase in cancer rates as red meat consumption increased. But that’s not what we see in many cases. In fact, in some studies you actually see a decrease in cancer rates in the people who ate the most red meat. (3)

Results are variable by anatomic tumour site (colon vs. rectum) and by gender, as the epidemiologic data are not indicative of a positive association among women while most associations are weakly elevated among men.

Translation: the studies claim that red meat causes different rates of cancer in different parts of the intestinal tract, and different rates in men and women. For example, in the study I just referenced above (#3), there was an inverse relationship between red meat intake and colon cancer (meaning people who ate more red meat had less colon cancer), but a positive relationship between red meat and rectal cancer. And in an analysis of data from the Women’s Health Study, researchers found a strong (and linear) inverse relationship between red meat consumption and colon cancer. (4) Without a clear explanation of why red meat would be prevent some types of intestinal cancer while contributing to others, and have different effects in men and women, the likelihood of a causal relationship between red meat and cancer is reduced.

Colinearity between red meat intake and other dietary factors (e.g. Western lifestyle, high intake of refined sugars and alcohol, low intake of fruits, vegetables and fibre) and behavioural factors (e.g. low physical activity, high smoking prevalence, high body mass index) limit the ability to analytically isolate the independent effects of red meat consumption.

Translation: the studies linking red meat and cancer are plagued by “healthy user bias.” This is a fancy way of saying that people who engage in one behavior perceived as healthy are likely to engage in other behaviors they perceive to be healthy. On the flip side, people who engage in one behavior perceived to be unhealthy are likely to engage in other behaviors perceived to be unhealthy.

In an ideal world, we would be able to conduct a randomized, controlled trial to determine whether red meat causes cancer. We’d create two groups of people that are relatively similar in age and other characteristics. Then we’d isolate them in a medical ward, strictly control their diet, exercise, and other lifestyle factors, and then feed one group more red meat and the other group less.

Unfortunately, this will never happen. Cancer can take decades to develop, so these poor souls would be living in a ward for at least 20 years. Even if we could find people to volunteer for such a study, it would be astronomically (and prohibitively) expensive.

As a result, we’re left to rely on observational studies to shed light on the question of whether red meat causes cancer. The problem with this is that observational studies do not prove causality—they just demonstrate an association, or relationship, between different variables. Sometimes the association is causal, and sometimes it’s not.

Let’s consider red meat. Regardless of whether consuming fresh and/or processed red meat is unhealthy, it has certainly been perceived that way for the past half-century in the industrialized world. What this means is that people in observational studies that eat more red meat also have a tendency to smoke and drink more, eat fewer fresh fruits and vegetables, exercise less, and engage in other unhealthy behaviors that could influence cancer risk. This isn’t just speculation; it has been shown in numerous studies. (4, 5)

For example, most Americans that eat red meat eat it with a huge bun made of white flour, with a serving or more of other refined carbohydrates (chips, fries, soda) cooked in rancid, industrially processed vegetable or seed oils. How do we know that it’s the red meat—and not these other foods—that is causing the increase in cancer?

The better observational studies attempt to eliminate the influence of these other factors, but in practice that is difficult if not impossible.

You Can’t See What You’re Not Looking For

What’s more, there are certain factors that are likely to play a significant role in the relationship between any food that we eat and cancer, but to my knowledge, have never been adequately controlled for in any study.

One of these is the gut microbiome. Previous work has shown that the composition of the gut microbiota may directly affect the influence of dietary factors on cancer risk. (6)

For example, Streptococcus bovis, Bacteroides, Fusobacterium, Clostridia, and Helicobacter pylori have been implicated in tumor development, whereas Lactobacillus acidophilus, L. plantarum, and Bifidobacterium longum have been shown to inhibit colon carcinogenesis. (7) Other studies have found that certain species of bacteria were higher in populations with high colon cancer risk, while other species were higher in populations with low colon cancer risk. (8) Finally, a recent paper compared the gut microbiota of 60 patients with colorectal cancer with that of 119 normal controls. The patients with cancer had significant elevations of Bacteroides/Prevotella (both species that are recognized as potentially harmful) when compared to the control group, and the difference was not affected by general patient characteristics (e.g., age, body mass index, family history of cancer), tumor size or location, or disease stage. (9)

We still have a lot to learn about the influence of the microbiome on health and disease, but we know enough already to conclude that it is significant. It is possible—and I would argue likely—then, that the variability we see in studies showing an association between red meat consumption and cancer may be in part due to the status of the patient’s microbiome.

In other words, a patient with a dysbiotic (i.e., compromised) microbiome may be at increased risk for cancer if he or she consumes high amounts of either fresh or processed red meat. But a patient with a normal, healthy microbiome may not be.

There is, in fact, some research that hints at this possibility—though it wasn’t what the study authors intended. A couple of years ago, scientists from the Cleveland Clinic published a paper linking red meat consumption with the production of a compound called TMAO, which has been associated with cardiovascular disease.

That paper was riddled with problems (which I outlined in this critique), including the most glaring one—that several foods, including seafood, increase TMAO production by a much greater margin than red meat. However, there was one section of the paper that I found to be very interesting.

It showed that omnivores who eat red meat produce TMAO, whereas vegans and vegetarians who hadn’t eaten meat for at least a year do not. The researchers claimed that this means eating red meat must alter the gut flora in a way that predisposes toward TMAO production.

However, there’s another explanation that I believe is much more plausible: the red meat eaters are engaging in unhealthy behaviors that lead to gut dysbiosis. This could include eating fewer fruits and vegetables and less fermentable fiber, while eating more processed and refined flour, sugar, and seed oils. All of these behaviors have been shown to be more common in the “average” red meat eater, and all of them have been associated with undesirable changes in the gut microbiota. (10, 11, 12)

Apples and Oranges (Or, Paleo vs. Standard American Diet)

Observational studies are useful for generating hypotheses and identifying general trends. But another limitation they suffer from, in addition to those I’ve described above, is that they aren’t able to detect the effects of crucial differences between study participants.

Consider two different people. One follows a standard American diet, doesn’t exercise much, and has a compromised gut microbiome. The other follows a Paleo-type diet, exercises regularly, and has a healthy gut microbiome. In an observational study looking at the relationship between red meat and cancer, at least 95 percent (if not more) of the red meat eaters in typical studies will fall into the former category. If the study concludes that there is a link between red meat and cancer, the 5 percent of the participants that eat a healthy diet, exercise, and have a healthy gut—and are thus highly unlikely to experience the same impact from eating red meat—will be lumped together with the other 95 percent.

Put a different way, it should be fairly obvious, given what we already know about the influence of diet, lifestyle, and the microbiome on cancer risk, that someone following a Paleo-type diet and lifestyle will not share the same cancer risk as someone following a Standard American Diet and lifestyle, even if they are eating an equivalent amount of red meat. Yet these two groups of people are always lumped together in the studies and media reports. This is a huge problem in research, and it has not been adequately addressed.

What’s the Bottom Line?

Even if you ignore everything I’ve written in this article and accept the WHO report at face value, just how much would your risk of cancer increase if you eat cured and processed meats?

About three extra cases of bowel cancer per 100,000 adults. That means you have about a 1 in 33,000 chance of developing bowel cancer from eating cured and processed meats.

This is a far cry from how much smoking cigarettes, which the WHO now classifies in the same category as eating bacon and salami, increases your risk.

As Professor Ian Johnson of The Institute of Food Research said in an interview with The Guardian:

It is certainly very inappropriate to suggest that any adverse effect of bacon and sausages on the risk of bowel cancer is comparable to the dangers of tobacco smoke, which is loaded with known chemical carcinogens and increases the risk of lung cancer in cigarette smokers by around twentyfold.

What’s more, the report from the WHO classified 940 other agents, along with red meat, as potential carcinogens. In the Guardian article above, Betsy Booren, the vice-president of scientific affairs for the North American Meat Institute, put it in perspective:

The IARC says you can enjoy your yoga class, but don’t breathe air (class 1 carcinogen), sit near a sun-filled window (class 1), apply aloe vera (class 2B) if you get a sunburn, drink wine or coffee (class 1 and class 2B), or eat grilled food (class 2A). And if you are a hairdresser or do shift work (both class 2A), you should seek a new career.

At this point, given what the research indicates, I do not feel that modest consumption of cured or processed meat is likely to pose a significant health risk, provided you are doing other things right (i.e., nurturing your gut microbiome, eating nutrient-dense, real foods, exercising, etc.). I think there is even less evidence suggesting that we should limit consumption of fresh red meat, especially when it is cooked using gentle methods (rather than charring it) and when you eat “from nose to tail.”

Okay, that’s it for this year’s installment of “red meat won’t kill you.” See you next year!

265 Comments

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  1. They should really leave the meat eaters alone and not try to help them live longer. Trying to get meat eaters to stop eating meat is simply wrong, even if it results in cancer, heart disease, diabetes, arthritis, IBS and obesity.

    Be sensitive, keep your alleged fountain of youth to yourself. many would not want to live longer without bacon and burgers.

  2. This whole website is based on pseudo-science just like the whole Paleo diet is.
    Some of the healthiest societies in the world eat the most carbs and very little meat and dairy.

    • Like India? India has the highest rate of type 2 diabetes, heart attack, stroke, top 5 for cancer and 61% of adult females have iron deficiency anemia, and because of diabetes rate, over 50% of type 2 diabetics will develop early dementia, and 70% will die of heart attack. 70% have a gene defect from too many generations of vegetarianism. This makes them produce high levels of arachidonic acid, the precursor of inflammation in your body. The healthiest culture on earth are Masai warriors of Kenya. THEY ONY EAT MEAT, MILK, AND BLOOD FROM A COW. No veggies or fruit.

        • Mark Littlewood- Why can’t both diets (Blue Zones, as well as Low Carbohydrate/ High Meat)- be effective? Just because one diet is successful, doesn’t automatically mean the other isn’t. These are all “real food”, native diets. Many different diets work for many different groups of people. And the problem with the Inuit studies you cited was that they were done too late; in this time period, they were no longer eating their native, mostly meat/seafood diet. Once they changed to modern foods, their health deteriorated. Also, I would like to mention that there were other very healthy, mostly carnivorous populations as well: the Plains Indians and the Mongolians, among others. This is not to say that the more plant based diets of the Mediterranean and “Blue Zones” are also not healthy. I don’t think it’s an either/or situation.

          • I dont rule that out but the problem for me is that in todays world plant based are doing very well and it is very difficult to dodge bad meat, the factory farmed antibiotic fueled immitation of anything the pop’s you describe would eat. The big problem I have is that when people get the message out that meat is OK the general population do not read the small print, they are just getting good news about their bad habits and think its a licence to continue eating highly factory farmed meats from the supermarket. The healthiest option for the general population from a budget and convenience point of view is whole food plant based

            • Isn’t eating GMO, pesticide-ridden, nutrient -deficient plants just as harmful as eating animals that ate GMO, pesticide-ridden, nutrient -deficient plants? If so, isn’t it just as dangerous for people to hear the message that “eating plants” is OK? How is it more difficult to dodge bad meat than bad plants? Isn’t it harder (not impossible) to get the nutrients you need from plants than from meat?

              Plant foods are cheaper, calorie for calorie, but does that mean they are cheaper based on total nutrients? I think your assumption that “plant based are doing very well” might need further inspection.

  3. Taken from your cited (3) paper defending red meat

    “Red meat intake was associated with increased risk of cancer of the rectum, with evidence of a dose–response relationship.”

  4. Do a little research on present Africa and you will find that their modern diet is about the same or worse than in the US with one exception, they consume little meat. However, colon cancer is just about non-existent.
    Forget all your research and find something in Africa that explains the low colon cancer if not the limited meat consumption because it is not more fiber or less processed foods than we consume in the US…

    • They also eat very little sugar, that’s another explanation
      You’re making the same mistake this article is pointing out.
      Saying red meat causes cancer because a group who avoid it don’t get cancer is not even close to a cause and effect. There is a million other factors involved.
      If this was the case why do vegans still get colon cancer / heart disease / diabetes, which are all supposed to be what red meat causes.

      People who eat red meat, eat breads, sugars and probably don’t work out much, as everyone thinks “red meat causes cancer ill stay away from that”, so the majority who eat it don’t give a fuck and probably do a lot of other damage to their bodies from other sources.

      The red meat thing has been going on for 60 years almost, and it initially started as a guess from little accurate research, but because your doctors, the government and the world has been spouting it as gospel ever since, no-one wants to admit the’re wrong now all this new research is coming out.

  5. 1 in 2 people in the uk will experience cancer at some point in their lives. Go figure! And McDonald and all the processed foods are aimed at children. Makes me sick.

  6. I have been training for close to 32 years i will be 45 in June, i recently stop the protein shakes and switch to a Intermittent fasting whole food diet, i never smoked or drank alcohol, i did eat junk and sugar food that i am cutting now.

    I recently added meat and eggs to my diet on a daily basis because they are the highest source of protein you can have and the Guru Vince Gironda was very fond of this too.

    Vince Gironda at the age of 46 did a 10 month of eating twice per day eggs and steak….. he looked amazing he did a carb up every 4 5 days and used is 8 x 8 program.

    There is a lot of propaganda with the vegans and meat i read a few books about the vegetarians and its like a religion.

    Meat is important for a man even more to keep high level of testosterone and have all the vitamins and mineral we need.

    I always buy low fat ground beef and steak sandwich those are fat free.

  7. Here’s a scientific paper from Meat Science journal, that not only explains why the studies that found red meat to be a cancer risk factor are questionable, but also indicates why proper consumption of red meat is actually good for your health, and might reduce risk of cancer:

    http://www.sciencedirect.com/science/article/pii/S0309174009002514

    People… you have to understand… the processed sausage, bacon, and burgers we buy at the supermarket or Mcdonalds have a ton of bad stuff in them (like high fructose corn syrup). Correlation DOES NOT equal causation. And guess what, people who tend to eat more red meat, don’t care much about their health (due to people so worried about their health follow the mainstream advice). So what we are seeing, is people with unhealthy lifestyles, who happen to eat a ton of red meat…

    • I still have a problem with the fact that amongst seven day eventists those that eat meat as opposed to being veggies have a 1.5 times risk of CHD. The risk increases with amount of meat consumed. This does at least take a cohort that are as close as you can get to being similar in outlook. I still think that sourcing grass fed free range meat is a minefield for the average consumer so the best advice is go veggie or perhaps only eat meat that is pretty much likely to be free range grass fed eg Rheindeer or Bison

  8. Seems to me that people invested in high protein diets (bodybuilders etc) and high meat diets (paleo etc) do not want to believe red meat causes cancer and will go the extra mile to pick apart the studies showing it probably does.

    • NeilC- I’ve said this before, and I’ll say it again. I got cancer after many years of being on a mostly vegan diet, with no red meat whatsoever. I am now almost 8 years cancer free after eating a Paleo, low carb diet with as much meat as I naturally feel like eating. I don’t think “they” know what causes cancer! Go figure…..

      • It’s possible that you are healthier now and cancer free because as following the Paleo diet you are avoiding processed foods, grains and sugar. Many people go vegan for humane reasons and know very little about health. A person can follow a healthy vegan lifestyle by avoiding these same things (processed foods, additives, grains, sugars, etc) eat more whole fruits and vegetables and improve in health without the consumption of meat.

        • Binx- yes, all true. When I was eating mostly vegan, I ate a lot of grains, both whole grains as well as white, and lots of white rice, etc. I was also less concerned with sugar, as the dietary advice at the time seemed to look at it as being benign. Though I wasn’t eating huge amounts of dessert and white sugar, I was eating a very high carb, high glycemic diet, which would have turned to sugar in the body; as well as fruits, muffins baked with some kind of sweetener (like maple syrup), etc. I also ate a lot of foods that I personally couldn’t digest properly, like starchy beans. Though at the time I thought I was eating a healthy diet (because I was avoiding meat), I don’t deny that there are healthier vegan diets out there- (though I seriously don’t think vegan is for everyone!) I was mostly making the point that I don’t believe meat causes cancer. There have been many hunter gatherer societies who ate high meat diets and yet had no cancer whatsoever. In my case, meat certainly wasn’t the cause of my cancer, and since I’ve started eating it again, I haven’t relapsed (at least not yet). I have a personal problem with people who are convinced that meat causes cancer and going vegan will cure all ills because I, too, used to believe this! I learned the hard way.

      • Hi Morgana,
        if you dont mind me asking what cancer did you have and which treatments? Also, how long prior to diagnosis was you vegan? Furthermore, yes there are and have been hunter gatherer societies but no way of knowing if cancer was the cause of deaths within them.
        thanks,
        Darren

        • From the EPIC Oxford study

          “Within the study, the incidence of all cancers combined was lower among vegetarians than among meat eaters, but the incidence of colorectal cancer was higher in vegetarians than in meat eaters.”

        • Darren- This is a very late answer. The kind of cancer I got was ovarian, not colorectal, as Mark Littlewood implied. Ovarian cancer is associated with- (not necessarily caused by)- vegetarian and vegan diets. Although Seventh Day Adventists have a lower cancer incidence than the general (American) population, they do have a higher risk of ovarian, as well as prostate cancer, than the general population. But mostly, I believed a vegan diet would keep me from getting cancer- (and that meat would cause disease). So I ate a diet that didn’t feel good to my body, because my head believed I was doing the right thing. (I was mostly vegetarian for about 5 years, and vegan for about 2 years before I was diagnosed; this is an estimation though, I don’t know exactly). Now I feel much better eating low carb with poultry, fish and meat. This is the diet that suits me much better.

  9. The title is a little sensational, but I like the article.

    Here’s the thing though, while it’s possible red meat isn’t the true cause, there’s also no benefit to eating it. So at worse it gives you cancer, at best it does nothing but provide you nutrients you can get elsewhere easily.

    Keep in mind, moderate, under 500g cooked weight of red meat is said by the WHO to be ok to eat per week as long as it’s fresh.

    The gut hypothesis could be true, but we don’t really know what microbiome is ideal and how to get it. Not yet, so it’s not a practical advice.

    Also all diets are simply recommendations, and all studies are probabilities. You can do all the wrong things and still live long and healthy if you’re lucky. So if you want even more chances on your side then avoid red meat as much as possible. How much more chances it’ll give you isn’t really known yet, and it’s hard to know, so pick your battles. Doing more exercise, being less inactive, sleeping more, keeping your brain challenged, eating more fruits, veggies, good fats and keeping your weight down will all help your chances also. There’s probably other things too like drinking less, keeping your stress low, stop smoking, move to a less polluted area, making sure your walls agent moldy, avoiding unneeded antibiotics, etc. Up this you to decide how many of these you’re ok doing. In the end, living longer and being healthy is only worth it if you still enjoy some things in life.

  10. This is the most stupid thing I’ve read in… years!
    Really, you’re seeing (so desperately) what you wanna see…
    Just SEARCH in scientific search engines like PUBMED or EBSCO: “meat and cancer” OR “diet and cancer” or JUST “diet and health”… and MOST studies you’ll find will say what’s obvious… RED meat consumption DO have a strong relation with a huge variety of cancers, and also a VERY STRONG relation with heart failure.
    This is not to discussion, thousands of studies came to the same conclusion, why in the world are you trying to prove otherwise? Against the opinion of very qualified medical comunity…
    I can only think in two reasons:
    1. You’re an as*hole, really, if you love red meat so much, IT’S OK! It’s a free country, feel free to eat as much red meat as you can, no one is taking you that right. What you eat and don’t eat is totally up to you. But red meat, will still be carcinogenic and principal cause of heart failure, and it doesn’t mean that all the doctors in the world are against you, you sound like you’re taking these news very personal, it’s just medicine man, it doesn’t matter how many tantrums you make, that won’t change, grow up man!
    2. You’re part of OR paid by the livestock industry… it is very well known that livestock industry is VERY angry after the WHO decisions on meat, it wouldn’t surprise me that all of these cheap articles were paid by ’em.
    Good luck eating red meat, you’ll need it
    PS: Get a good health insurence, you’ll need it too

    • I am amazed at the number of trolls with negative and sometimes insulting comments. If they disagree in principle with eating meat, why are they on this website to begin with? Besides, the WHO/IARC report was biased from the start and supplemented with cherry picking. To base a study on reports from the recipients is only a survey, not science. So, how many people ate only red meat? How many high carbs? There is no cause and effect proven.

      • Indeed, I think that the WHO has been bought by the powerful brussell sprout lobbying group but then I’m just an old fashioned conspiracy theorist. People have a right to be on here to learn about health and when they disagree they should do so. I think Chris is very wrong on this and is giving the wrong message but to his credit he has not, to my knowledge, censored people.

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