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We're a little crazy, about science!

Steak raises cancer risk and now we know why

steak

Some of you may remember a recent study showing why red meat is bad for the heart, while now there is a study showing why steak — or in particular red meats — raise the risk of cancer. To be clear, I am still very much a red meat eater and this is no way intended to change anyones opinions on steak consumption, but it is nice to understand the science behind what we put in our mouths.

It has been known that people who eat a lot of red meat are at higher risk for certain cancers while other carnivores are not without a clear cause as to why. This prompted researchers to investigate the possible tumor-forming role of a sugar called Neu5Gc, which is naturally found in most mammals but not in humans.

The scientists found that feeding Neu5Gc to mice engineered to be deficient in the sugar (like humans) significantly promoted spontaneous cancers. The study did not involve exposure to carcinogens (which artificially induce cancers), further implicating Neu5Gc as a key link between red meat consumption and cancer.

“Until now, all of our evidence linking Neu5Gc to cancer was circumstantial or indirectly predicted from somewhat artificial experimental setups,” said principal investigator Ajit Varki, MD.

“This is the first time we have directly shown that mimicking the exact situation in humans—feeding non-human Neu5Gc and inducing anti-Neu5Gc antibodies—increases spontaneous cancers in mice.”

The team first conducted a systematic survey of common foods. They found that red meats (beef, pork and lamb) are rich in Neu5Gc, affirming that foods of mammalian origin such as these are the primary sources of Neu5Gc in the human diet. The molecule was found to be bio-available, too — which just means it can be distributed to tissues throughout the body via the bloodstream.

The researchers had previously discovered that animal Neu5Gc can be absorbed into human tissues. In this study, they hypothesized that eating red meat could lead to inflammation if the body’s immune system is constantly generating antibodies against consumed animal Neu5Gc, a foreign molecule. Chronic inflammation is known to promote tumor formation.

To test this hypothesis, the team engineered mice to mimic humans in that they lacked their own Neu5Gc and produced antibodies against it. When these mice were fed Neu5Gc, they developed systemic inflammation. Spontaneous tumor formation increased fivefold and Neu5Gc accumulated in the tumors.

“The final proof in humans will be much harder to come by,” Varki said. “But on a more general note, this work may also help explain potential connections of red meat consumption to other diseases exacerbated by chronic inflammation, such as atherosclerosis and type 2 diabetes.

“Of course, moderate amounts of red meat can be a source of good nutrition for young people. We hope that our work will eventually lead the way to practical solutions for this catch-22.”

Unfortunately, the study done in mice will probably be the somewhat final word on the matter and further research still needs to be done. However, it would be nice to at least understand why red meat consumption increases cancer risk and even find ways to prevent the problems that come from heavy consumption.

Sources
Samraj, A., Pearce, O., Läubli, H., Crittenden, A., Bergfeld, A., Banda, K., Gregg, C., Bingman, A., Secrest, P., Diaz, S., Varki, N., & Varki, A. (2014). A red meat-derived glycan promotes inflammation and cancer progression Proceedings of the National Academy of Sciences DOI: 10.1073/pnas.1417508112

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4 responses

  1. Jim F

    What is really hard to understand is why you continue to eat red meat. I am an 80 year old converted gradually to a vegan lifestyle. I feel better than I did in my 50s.

    December 31, 2014 at 3:00 pm

    • Because meat isn’t bad, because a vegan diet is overly restrictive, because it is at best no better than a carnivorous diet we evolved to enjoy and at the worse is horrible for you (which is most vegans anyway).

      Not to take away from how you feel, which is great and I’m happy you found something that makes you feel good, but that is hardly scientific.

      Most people who switch diets like that typically ate even worse anyway and only see an improvement from it because it’s slightly less horrible than how the person was eating beforehand.

      A vegan diet is awful and baring some odd medical condition where dairy and meat cause issues, has been shown time and time again to be worse than just a normal, less arbitrarily restrictive diet. Same goes for “gluten free” actually, both diets by the way have been studied ad nauseum.

      December 31, 2014 at 5:46 pm

  2. jack

    1. Citations would be appreciated on the author’s assertion “it is well known that…[eating red meat increases risk of cancer]” and on your assertion “It has been known that people who eat a lot of red meat are at higher risk for certain cancers while other carnivores are not”, not to mention some elaboration, since neither is well known to me, despite being somewhat familiar with the literature. This is coming across as a possibly false assertion in the “urban legend” category, and I’d really like to be better convinced of this foundational hypothesis, let alone the validity of extrapolating the results of the mouse study to human health.

    2. The PNAS paper itself would be nice to read, but alas I didn’t want to pay $25 to do so at the PNAS website, so I’ll have to try to find it at a library or something. Sorry for being cheap, but to stay up on the actual publications in any number is really expensive. I’ll find a source at some point, or buy access, but at this point I have not. So my following points may simply be off-base, not having read the actual paper. But then again, maybe they are right on target.

    2a. My own primary, bold, “uncitationed” assertion, analogous to the ones made above, is that the rodent immune system is nothing like the human immune system, or so I have been cautioned repeatedly by numerous professors of human and rodent biology at the graduate level in several institutions of higher learning. Further, a casual search of the literature shows that cancer of many kinds has been cured, over and over, in rodents, but results have yet to translate to human cancer cures (Bummer!). These two facts (or assertions if you like) give me great pause in extrapolating anything at all to human (really just my own ) health based on these sorts of rodent studies.

    2b. Assuming there is extrapolative value from rodent study to human, many questions still arise regarding the rodent study, such as…

    -What happens when they are fed an actual food diet containing a high amount of red-meat, similar to what a human on an Atkins-like or Paleo diet might eat, as opposed to somehow ingesting (drinking?) a liquid solution of dissolved neu5gc at questionable concentrations? Can any conclusions about eating real food ever be made from a study that doesn’t involve actual eating, nor of actual food?

    -What does the author mean that the mice were then “challenged with antibodies”? That sounds like a whole lot more going on than the mice ingesting the compound then developing an immune response on their own, which is what we are told to infer is likely happening in people. That sounds like a lot of reaching. Just saying. So, the knockout mice didn’t naturally make their own antibodies to the neu5Gc? What kind of changes were done to the mice besides knocking out their neu5gc-producing enzyme? Was their immune system altered too? Has such immune system alteration ever been shown to translate to anything like human immune response, which itself is poorly understood, mind you?

    All that said, the author(s?) have been researching this compound and relation to mammalian cancer for over a decade, and their past publications combined with this one are very intriguing, especially to me as a fairly strict paleo eater. A nice Review-type paper of everything to date on consumption of this particular compound, related immune response and cancer, all in one spot, and with full citations, (none of this “it is well known that” stuff), would really be nice right about now. And really valuable would be, as already mentioned by others, an actual human study.

    Cheers!

    January 2, 2015 at 2:06 pm

    • Wow and I thought I typed long comments! First thank you for the thoughtful and through reply to my post. I’m going address some of your concerns backwards as it is easier for me to work my way up your comment then start from the top and go back down.

      I agree that a meta study of all the data linking back to the sources would be great. Harvard had a great page on the subject that I liked to site, however the only page I could find (admittedly I am busy at the moment) was this one that referenced sources without actual citation: http://www.health.harvard.edu/fhg/updates/Red-meat-and-colon-cancer.shtml

      I do apologize for the language, I try to over simplify sometimes so it is easier to say “well known” bad habit, I know.

      2b. The knockout mice variable was just to help isolate what was going on, I’m sure you understand that bit. However your concerns are very valid and it was most likely assumed (from what I can gather from the study) that there was no known changes to the immune system so it (should) have no effect on the outcome of the study

      Feeding red meat to mice would be hard to do, so doing a mice study on red meat consumption is difficult without using the specific compound you are trying to test. I agree that testing individual responses to something instead of as a whole can be variable in the conclusions and trying to extrapolate the information is dangerous.

      2a. I don’t particularly care for mice studies without human trials which I tried to make clear at the end of my post. I also try to make clear that it isn’t going to dissuade me from eating meat anytime soon as well.Mice studies are useful however and I do enjoy the nice bit of controversy around what we eat. Skepticism is good though and I hope we get human studies to hopefully put this to rest (At least for a little bit).

      2. If you want access to the study, most universities (if you are affiliated with one) have access for students, alumni, teachers, etc. To be honest with you I didn’t dig too deep into who they cited their work on so I couldn’t go into depth on the matter. Keep in mind that between work and life I am fairly busy so managing the blog is on the bottom of the list of things to do.

      1. The author does cite some basis for their claim, but as I said before how good that research is I do not know.

      Hope that helps clear something up, if it sounds like I am rambling like a lunatic you will have to forgive me, it has been a long day.

      Thank you for taking the time out of yours to comment and I truly hope you find the answers about the study you are looking for, you are more than welcome to comment once more if you do find anything of interest.

      Also, you can now see what I mean by long comments 🙂

      January 2, 2015 at 5:21 pm

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