So Meat Causes Cancer Now? Dr. Kern Explains.

Guest post by Dr. Joshua Kern

Forward from Amber: pretty much everyone has written about the ‘MEAT CAUSES CANCER OMG’ news from the World Health Organization last week. You know me, I like to put things in perspective for you guys so you don’t have to run out and completely overhaul your entire diet and lifestyle if it’s not totally necessary. For this one, I asked my friend and coaching partner Dr. Joshua Kern to take a look at the study and provide some perspective and, well…balance for you. At the end I’ll list some of my own blog posts on other media-hyped-up health news reports like this one. So now, without further ado, Dr. Kern’s post. Enjoy!

Virus

Recently the World Health Organization released a report about processed and red meat and rates of cancer. You probably saw some coverage of it in the media.

The viral nature of both the mainstream media reaction and the science-minded backlash to the “meat causes cancer” news following this report have been fascinating to witness.  I think the strong emotions this report provokes make a pretty good case study on the reactionary nature we have when it comes to health in Western nations. As a culture we’ve become obsessed with health, as we’ve realized that we probably aren’t doing it right.  But despite the answer being pretty basic (eat more vegetables, exercise more, and eat enough to support healthy activity and weight – so simple, yet so hard to implement) we are always looking for “it”- that singular piece of news or supplement which will finally get us down the road to health. I feel like the reaction to the WHO report is no different.

Many bloggers have already covered this report, some with a balanced and science-minded view but some quite biased in favor of various diet ideologies. I saw a great piece by examine.com that looks at the science of the article and ends with a very commendable and moderate summary:

“But all that being said, the evidence is mostly observational or mechanistic in nature. Due to the practical impossibility of running multi-decade controlled trials, the increased risk from eating different amounts of red meat is not really known. In this case, as in many others, moderation may be key.”  

I don’t think I need to beat the dead horse that this report is based on pretty low-quality evidence that shows correlation only, not causation.  A diet high in processed meat also tends to be low in vegetables and fruit and associated with a lifestyle high in other risk factors for cancer. So with the type and quality of evidence in this report, there is no way it can “prove” it’s the meat that’s the issue, and yet most media coverage of it stated that a link had been proved between processed and red meat and cancer. It’s been a reaction typical of how our culture treats questions of health and lifestyle.

I’d like to spend a moment putting the reported increase in risk in context. I don’t know if we can blame “increased risk” hysteria on low science literacy of the media or the people reading it. I suspect both. We humans tend to make decisions based on fear, not fact.

One example of this is the absolute fear of hormone replacement therapy that’s ingrained already in American culture since the Women’s Health Initiative study was published in 2002. When I have very uncomfortable menopausal women as patients and suggest that we consider hormones, you’d think I was recommending cyanide pills to them.  The fact is that this fear is because of a very, very small increased risk of heart disease which was misrepresented somewhat in the initial paper and in the lay media. Something important to understand about that big study was that the average age of the women was about 75. They were taking women who had been menopausal for an average of 25 years and putting them on hormones, and that’s the study that created all this fear and hysteria.  If you are 50, your risks and physiology are pretty different from someone who’s 75 years old. So right off the bat, how can we know if anything about this study applies to an early menopausal woman with crippling hot flashes?

The actual risk of hormones increasing cardiovascular disease in the study was quoted widely as “29%”. This is only sort of true – that number is based on a hazard ratio of 1.29. The absolute risk was very small, because even the women in the hormone group had so few heart attacks!  The total number of women in the hormone group had a .37% incidence of heart disease in a group of 10,000.  The placebo group had an incidence of .30%, which means the actual absolute increase in risk was .07%.  I personally would make very few medical decisions about myself based on absolute risk increases that low. In fact, with some reanalysis, that increase in risk wasn’t felt to be statistically significant, meaning that there’s a very good chance that finding was related to random chance. Yet many people still make decisions about hormone replacement based on the fear generated by the misrepresentation of low-quality data from one study. For more information on the reanalysis of that paper view this: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1630688/

With that example in mind, let’s turn our attention to the increased risk reported in the WHO report about meat.  This PBS article is pretty typical of the types of reporting that people were reading and then freaking out about eating meat.

From that PBS article:

“That meta analysis found that colorectal cancer risk jumps by 17 percent for every 100 grams (3.5 ounces) of red meat consumed each day. Meanwhile with processed meat, colorectal cancer risk increases by 18 percent for every 50 grams (1.7 ounces) eaten each day.”  

Before we jump on the “OMG increased risk!” bandwagon, let’s objectively look at what that even means by putting it in perspective.  Again, I’m ignoring the fact that this report doesn’t actually prove an increased risk. It indicates a correlation, and the authors of one of the biggest studies used to create this WHO report actually state,“In the large prospective cohort of American Nurses (NHS), it was estimated that women who consumed high amounts of red and processed meat, did not exercise, had a low folate intake, and had a consistent excess in body weight.”  http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0020456

Ignoring those other factors and pretending that this is a real effect purely from the meat, we are going to take these numbers at face value. The baseline risk of an average person for developing colon cancer is about 5% in their lifetime. By eating one hotdog per day every day of your life you increase that risk to 5.9%. That’s what these numbers say.  I’d argue that everyone knows that eating one hotdog per day is probably not optimal for health, but even if you did eat one every day, the overall increase in risk seems pretty small to me. Should that keep you from ever eating a hotdog? That’s for you to decide. I’ll continue to eat a few hotdogs a year when I go to a ballgame because that’s what I do when I go to a ballgame.

To put this increase in risk in further perspective, what’s the increased risk of developing colon cancer if you have a family member who had colon cancer?  That’s one of the biggest known risk factors. The increased risk of that is more like a true doubling from 5% baseline risk to 10% baseline risk. To me that’s a truly significant increase in risk, but it still means that if one of your parents had colon cancer you still have a 90% chance of NOT getting colon cancer (though I still recommend all adults follow colon cancer screening guidelines anyway).

I hope that helps put this report and the reaction to it in some perspective. This is why I don’t change my diet every time a headline comes out that claims “this kills you” or “that saves you”.  I think a recommendation to eat more fruits and vegetables and get more exercise is one of the things I can really get behind, because the level of evidence is pretty overwhelming that it improves health. It’s just not sexy because it’s so…moderate.

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Dr. Joshua Kern went to medical school at University of Washington. He practices Family Medicine in a small town in southern Idaho where he does a little of everything including colonoscopy, delivering babies, and inpatient medicine. He runs a residency and trains family medicine doctors and medical students. He’s an assistant clinical professor at the University of Washington.

He lives with his wife and three children. He also is a lifter of heavy things, and author of the blog Go Maleo. He’s my partner in moderating my Facebook group Eating the Food, a friend, and an all-around awesome person.