No, Veganism Doesn’t Cure Cancer

I was recently subjected to an atrocious meme — think the sort of out-of-context, hyperbolic, grammar-impoverished, citation-free, viral images that helped elect Donald Trump. Lucky for you, I can’t find it anywhere, so your eyes are safe for the time being.

The meme said something along the lines of: “Nobel prize winner finds veganism cures cancer!” It’s portrayed as some stunning breakthrough in which, finally, veganism will be recognized for the cure-all many vegans think it to be.

The study that this meme was based on was published in 2013 in The Lancet. The lead author on the paper is Dr. Elizabeth Blackburn, winner of the Nobel Prize in Physiology or Medicine 2009 “for the discovery of how chromosomes are protected by telomeres and the enzyme telomerase.” (My understanding of the relationship between telomeres and cancer is that telomeres act as a sort of aglet that prevent chromosomes from becoming damaged, which can lead to the development of cancer. Or something like that.)

Co-author Dr. Dean Ornish is a well-known and outspoken advocate for plant-based diets. I believe it’s fair to say his life’s work is “proving” that veganism, in combination with exercise, is the fountain of youth. Ornish, as well as naive readers and unscrupulous journalists, often report on his research (which typically features very small samples) as proof that veganism, not a broader lifestyle change, cures cancer.

This study in particular recruited men who all had “biopsy-proven low-risk prostate cancer.” The researchers compared ten men who received the intervention — “comprehensive lifestyle changes (diet, activity, stress management, and social support)” — with 35 men who did not receive any intervention.

After 5 years in the respective conditions, the researchers “took blood samples […] and compared relative telomere length and telomerase enzymatic activity per viable cell with those at baseline, and assessed their relation to the degree of lifestyle changes.” In other words, they looked at how five years of drastic changes in diet, activity, stress management, and social support, corresponded to telomere length and “enzymatic activity.” Was there a change for those in the experimental condition? And if so, how does this change compare to those in the control condition?

They found that telomere length increased in the intervention group and decreased in the control group. They also found that the degree to which the ten participants adhered to the lifestyle changes was a significant predictor of telomere length. These findings suggest that the intervention worked.

There are several problems with this research that present significant limits on the conclusions that can be drawn.

As we’ve discussed before, the health benefits of a vegan lifestyle have yet to be conclusively demonstrated. One of the reasons is that research such as Ornish’s does not isolate the veganism variable from the other variables. For instance, it could be that case that the exercise portion of the lifestyle intervention accounts for these apparent changes. It could also be the case — though unlikely — that the lifestyle intervention would be even more effective without the plant-based diet. And it could also be the case that the diet is solely responsible. We simply don’t know.

As others have pointed out, this was not a randomized controlled trial. The sample was very small, and the participants who successfully maintained 5 years of comprehensive lifestyle changes were undoubtedly different from the others in important ways.

As mentioned, all participants had prostate cancer — which may indicate an unhealthy lifestyle at baseline. What if the improvements are simply a result of shifting away from an unhealthy lifestyle, and not a result of moving toward a healthier one?

Unfortunately, Ornish’s research commonly features outsized conclusions following shaky evidence. In another paper in which Ornish again teamed up with Blackburn, it is claimed that a vegan diet caused more than 500 genes to change in just three months. Curiously, I could not find the original paper, so we’re relying on journalists to get it right.

Again, the intervention was the same. It was not just a plant-based diet, but regular exercise, more social support, etc. These changes cannot be attributed to veganism, but Ornish isn’t doing much of anything to make this point clear. (As an aside, I previously read an article that quoted Ornish as saying that the 500 genes changed in a positive way “every time,” a claim that I simply don’t buy.)

I hope that Ornish’s lifestyle intervention really works. I suspect that it does. I also hope that veganism contributes to these positive effects, as that will add a solid third pillar to the case for adopting veganism — and quite an attractive one at that.

But it’s currently too early to tell, and these sorts of unwarranted claims can actually be dangerous when taken too seriously.


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  1. Here’s the paper:

    The study was done on 31 men with prostate cancer. The term “changes” includes good and bad: 48 genes producing cancer cells were MORE active after the three months, but that was overshadowed by the 453 genes responsible for producing tumor proteins have LESSENED their tumor production after three months on a plant based diet…AND the introduction of an active exercise routine.

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