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Cracking open the claim that walnuts “may help slow colon cancer growth”

New Harvard research finds walnuts may help slow colon cancer growth A walnut-enriched diet may cause beneficial genetic changes in animal cancer cells, affecting inflammation, blood supply and growth of tumors

Our Review Summary

Mice are not people. Yet many medical research headlines about mouse studies extend the implicit promise that whatever is discovered may cure diseases in humans. This release tries to correct that by mentioning “animal study” in the sub-headline and in its first sentence. That’s more than many releases would do, but the main headline (not the subhead) is what appears in search results about this release, and we still worry most people will assume the wrong implicit promise.

The study discussed here is about the biochemistry surrounding certain genetic changes in mice fed walnuts while growing colon cancer tumors. It appears the mouse tumors grew more slowly in the mice fed the equivalent of a human diet of two ounces of walnuts per day. The study is trying to unpack the mechanism of that impact. And apart from the headline, it mostly does a satisfactory job of communicating the results of the study in a responsible, measured way.

But let’s remember that these findings in mice are many years away from any human application. And yet a public relations company connected to the California Walnut Commission is very eager to make sure you — probably not a cancer scientist, but definitely a human potential walnut consumer — are aware of what happened in these mice. Yes, the study carries tantalizing information about the way the walnut diet appears to influence the genetics of colon tumors — in the mice — but it will take much more investigation before it yields the kind of results that warrant a headline, “New Harvard research finds walnuts may help slow colon cancer growth.”


Why This Matters

According to the National Cancer Institute, colorectal cancer (CRC) is the third most common cancer worldwide and the second leading cause of cancer deaths in the United States. If something as simple as eating walnuts could reduce that risk or slow down cancer progression, it would matter quite a bit.


Does the news release adequately discuss the costs of the intervention?

Not Applicable

In this very narrow discussion of a small study in mice, the suggestion is that someday maybe walnuts (or some nutritional element of walnuts) could help people by slowing the growth of colon cancer. But while the study doesn’t mention how much (or how little) such a therapy might cost, we think this criterion is Not Applicable here for two reasons: 1. the cost of walnuts is generally well known, and 2. the research is at early enough stage — and the release establishes the preliminary nature of the study — that it’s hard to know what any walnut-related therapy might cost.

Furthermore, while the criteria of cost is integral to what we all agree is good reporting about health outcomes, incorporating information about the potential cost of walnuts — or any other foodstuffs — in a release about a study that’s so preliminary might actually reinforce the suggestion of a useful therapy. Including that info wouldn’t improve anyone’s understanding of the importance of the research.

Does the news release adequately quantify the benefits of the treatment/test/product/procedure?


The research on a small group of mice showed slowing of the growth of colon cancer tumors. The research proved that tumors in mice fed walnuts had “10 times the amount of total omega-3 fatty acids, including plant-based alpha-linolenic acid (ALA), in the tissue compared to the mice fed the control diet.” Although the quantification here is limited, we’ll give the story credit for accurately reporting the outcomes in broad strokes. The detailed results of what happened in a mouse study have limited use for the average human reader anyway.

But while the release does not state that the mouse study could lead to prevention for humans, we’re worried that a normal reader may see the suggested effects of an enhanced walnut diet — increased anti-inflammatory activity, reduced angiogenesis, increased protective lipid content — and assume that these affect actual cancer outcomes. Set aside the major caveat that it is an animal study for a moment — the release says that walnuts “may” slow the growth of colon cancer.  It also equally may not.

Does the news release adequately explain/quantify the harms of the intervention?

Not Applicable

The limited study did not appear to investigate potential harms, and the release didn’t comment on them. For humans, consumption of too many calorie-dense walnuts could precipitate weight gain. But the equivalent of two ounces a day doesn’t sound like it could be very harmful. We’ll rate this Not Applicable.

Does the news release seem to grasp the quality of the evidence?


While the main headline was not upfront about the fact that the study involved mice, the body of the release itself was carefully worded and did a fair job of describing the evidence. It’s always helpful to see “animal” in the very first sentence of a study involving mice.

microRNAs are a complicated topic, as are changes in gene expression, which is at the root of the questions that the study addressed. The release adequately describes the evidence drawn from the work but does so sparsely. The eight-page paper is reduced to an eight-paragraph release, only three paragraphs of which actually convey an explanation of the work. What the release offers is acceptable by our standards but more information, properly couched, could aid readers in assessing the study’s true value.

Does the news release commit disease-mongering?


There was no disease mongering.

Does the news release identify funding sources & disclose conflicts of interest?


Funding sources were identified, netting this release a Satisfactory rating, but when a fundor is integrally related to the substance of the research, that mention belongs higher up in the story or release, rather than tagged onto the end, allowing readers to consider the context of the funding early in their reading of the material.

Does the news release compare the new approach with existing alternatives?

Not Satisfactory

The release discusses the chemistry of inflammation and the growth of tumors in the mice. It briefly mentions “diet and lifestyle changes” as means to reduce risk, but does not discuss what specific changes are shown to be helpful. It also does not discuss screening and polyp removal, arguably the best-supported intervention for catching colon cancer before it spreads.

Does the news release establish the true novelty of the approach?


There has already been research on the potential protective influence of omega-3 fatty acids for inflammation. The release clearly explained the novelty of this specific mouse study investigating underlying chemistry and how it may work.

Does the news release include unjustifiable, sensational language, including in the quotes of researchers?


While we aren’t happy with the headline, we think this release squeaks by because the main text is accurate and we applaud the first sentence clearly labeling it an “animal study.”

The release clearly avoids any sensationalized verbiage, a feat to be lauded in cases like this when an inference of a simple activity — like eating nuts — might lead a reader to jump to wrong conclusions.

Total Score: 7 of 8 Satisfactory

Comments (2)

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December 28, 2015 at 8:25 am

I appreciate your concern about dishonest reporting. But pick on something more dangerous than walnuts, perhaps. Like drugs-not walnuts. Walnut eating is good. They don’t seem to cause cancer, obesity, or anything else that will kill you, unlike the vast array of procedures that might kill you or get you very sick. I would encourage you to stop reviewing fruits and vegetable claims altogether. If the world gets tricked INTO eating them, then that’s not a bad result. Consider the tremendous buying power wherein inappropriate observational studies were widely used to dissuade people from the concern about saturated fat consumption and wound up having butter on the cover of Time magazine. Demonize that to your heart’s content, and you will be doing a great service.


    Kevin Lomangino

    December 28, 2015 at 8:48 am

    Thanks for your comment Richard. We think any “trickery” in health news is unacceptable, and walnuts are no exception. As your comment seems to acknowledge, the promotion or demonization of any one food or nutrient based on weak evidence can have unintended consequences. Selling walnuts as a way to slow colon cancer, based on a mouse study, is questionable at best, and such reports serve to erode the public’s trust in journalism and science. The end result of such erosion is an ill-informed public that is incapable of separating fact from fiction when it comes to health news. We hope to avoid that outcome by advocating for a higher standard.