What you need to know about claims that whole grains can prevent diabetes

Mary Chris Jaklevic is a reporter-editor at HealthNewsReview.org. She tweets as @mcjaklevic.

Check out these enticing headlines based on a recent study linking whole grains to lower diabetes risk:

If that’s not enough to make you stock up on quinoa and oatmeal, the Post offered this catchy lead: “Eat your Wheaties to avoid diabetes.”

But before you run the grocery store, consider why it might not be advisable to start eating more whole grains based solely on this study.

As we’ve written many times, observational studies such as this one can’t prove cause and effect; they can only show an association.

It’s possible that people who eat a lot of whole grain in Denmark — where this study was conducted — engage in other healthy behaviors or have other characteristics that make them less prone to diabetes.

While researchers may attempt to adjust the data to account for those factors, it’s not possible to know whether all of the numerous variables have been taken into account. The lingering effect of these issues is known as “residual confounding.”

Nevertheless, some news organizations love to feed the public’s hearty appetite for a dietary “magic bullet” — a single nutrient that will avert disease.

In this case, Chalmers University of Technology accommodated by serving up a heaping course of misleading causal language in its news release:

“It doesn’t matter if it’s rye, oats, or wheat. As long as it is wholegrain, it can prevent type 2 diabetes. … The comprehensive study is a strong confirmation of previous research findings on the importance of whole grains for prevention of type 2 diabetes.”

“Can prevent” diabetes? “Comprehensive” study? “Strong confirmation” of previous findings?

That’s not what the study authors actually wrote in their published paper. They concluded that they found “consistent inverse associations between whole-grain intake and the risk of type 2 diabetes.”

It’s possible this study constitutes a useful clue when considered in the context of other research, but on its own it does not prove that whole grains prevent diabetes.

News coverage wasn’t supported by evidence

Unfortunately, that more cautious message wasn’t transmitted to the public in these three news stories.

For example, HealthDay suggested the data did show cause and effect, writing: “Exactly how whole grains help prevent type 2 diabetes isn’t clear from this study.”

In the next sentence, HealthDay flip-flopped, acknowledging that suggestion wasn’t really valid: “Because it’s an observational study, it isn’t designed to prove a cause-and-effect relationship.” If that’s the case, why did HealthDay use cause-and-effect language earlier in its story?

The Post quoted a researcher suggesting the study’s findings challenge trendy low-carb diets. The Post advised: “So feel free to indulge in a slab of whole-wheat sourdough with dinner.”

With zero data, the Spectator asserted that the ability to use whole grain to prevent type 2 diabetes has actually “been known for a long time.” It reported that this study contributed data on the “role of different wholegrain sources” and “how much wholegrain is needed to reduce the risk of developing diabetes.”

Bias in nutrition research is under attack

In a recent op-ed that reflected widespread frustration with nutrition research, Stanford researcher John Ioannidis, MD, wrote that studies showing associations — often erroneously reported in the news media as demonstrating cause and effect — might erode public trust and harm public health.

“Unfounded beliefs that justify eating more food, provided ‘quality food’ is consumed, confuse the public and detract from the agenda of preventing and treating obesity,” he wrote in the piece, which appeared in the Journal of the American Medical Association.

He noted that in studies like this one, the estimates of benefit “probably reflect almost exclusively the magnitude of the cumulative biases in this type of research, with extensive residual confounding and selective reporting.”

In a recent interview with CBC News, Ioannidis more bluntly described nutritional epidemiology a “scandal” that “should just go to the waste bin.” Rather than embrace such research, he said news outlets should ignore it.

“What it ends up being is that you get things published that are what the investigators, the reviewers and the editors want to see,” he said.

Please note: Observational studies (as with the research that linked smoking to cancer and other problems) can indeed pile up such overwhelming evidence that it would be prudent to make public health recommendations on that basis. However, it’s rare that observational studies reported in the news media rise to this level of evidence. Moreover, an observational study cannot prove cause and effect. Statistical association is not proof of cause-and-effect. It is not unimportant. But no one should make it more than what it is.

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Comments (4)

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September 12, 2018 at 11:00 pm

I very much respect your almost-Cartesian approach and appreciate your voluminous output, but sometimes HNR feels a little formulaic, and sometimes no more robust and no less glib that the articles it is critiquing. For example, here we’ve given an uncritical repeat of an opinion from a doctor who thinks nutrition epidemiological health news ought to just stop (tell that to the plant-based health movement!!). First of all, this seems like a profoundly controversial if not ludicrous and offensive suggestion that is barely defended here. Second, we aren’t offered any contrary/different opinion to balance it (which is more crucial than it might otherwise be due to the eyebrow-raising nature of his opinion). Third, what are that doctor’s conflicts of interest, I wonder–if he takes research grants from diary interests, for an extreme example, we should know that. I tried to investigate it myself, but the article is behind a paywall so I can’t even check his first footnote, which cites the claim that nearly all foods have “significant association to mortality risk” (oh really, even broccoli, kale, potaotes, brown rice, beans, etc etc etc — simply No, that claim is overstated to the point of ridiculous). I actually have read quite a bit of the literature he is suggesting should be kept from the public, and I am a little offended by this very elitist attitude embraced here.
It just seems that in any newsroom, even HNR’s “newsroom” that “experts” who agree with the editorial point of view are offered uncritically to readers. But this is a fairly horrible point of view to embrace, I must say. Still love y’all and what you do, but wanted to offer this.

    Kevin Lomangino

    September 13, 2018 at 6:57 am


    Although we don’t normally post comments from people who don’t provide a full name, I’ll bend that rule in this case because you’ve raised some substantive issues that deserve to be addressed.

    First, I’m glad that we made you think about whether nutritional epidemiology should be reported on. This concept is neither ludicrous nor offensive. We’ve been documenting the problems with this type of reporting for years and while this particular post — taken in isolation — may not seem robust to you, it’s only one of dozens of such posts we’ve published on this topic.

    Our publisher Gary Schwitzer wrote recently about why we are paying more attention than ever to the problems with epidemiological studies and writing more of these types of posts:


    In addition, our primer on this topic provides a good overview of what’s wrong with most reporting on epidemiolocal studies:


    And you’ll find some links to a few of the dozens of posts we’ve written on this topic here

    If, like many news consumers, you aren’t aware of the major problems with these types of studies — and how those problems are rarely discussed in news coverage about them — then I can understand why you might be confused and offended.

    But this is an idea whose time has come and we are not the only ones who are raising pointed questions about this issue. More on the topic here:


    Finally, Dr. Ioannidis reports no conflicts of interest and you can learn more about him in this podcast:


    I don’t think it’s “elitist” at all to keep what is often useless noise from these types of studies from polluting our public discussion about health care. I hope you’ll take a moment to consider the substantive issues raised in this post and the dozens of others we’ve written on this topic.


    Kevin Lomangino
    Managing Editor

Valerie Sims

September 17, 2018 at 5:27 pm

Kevin, thank you for responding to Jesse, but I wish you had addressed other concerns that Jesse stated. The greatest concern is that most of us cannot access the full article and citations because they are behind a paywall. How can we learn from information that we cannot see without expense? How many articles that end up having no value to us as individuals must we pay to read and that were accessed based on the title and opening paragraphs with no readable citations? I myself believe most nutritional research is useless because it is reductionist, but all people need the same access as the author of the article. I would have appreciated Dr. Ionnidis’s opinions, and I think that your response, while correct in many respects, did not address the dominant questions that Jesse brought up. While we can look up Dr. Ionnidis’s credentials, we do not know if he has any conflicts of interest with this particular opinion piece. These are the elitist aspects to which Jesse refers.
Thank you for all the Health News Review does, but some of us want to take the next steps and are thwarted.

    Gary Schwitzer

    September 18, 2018 at 12:38 pm


    Kevin is traveling, so I’ll attempt to respond to your note.

    I’m sure you’re aware that we have no control over journals publishing behind a paywall. I share your concerns about the public’s lack of access to such papers which are often promoted by the journals but then not available to the general public. This is one component of the tsunami of health care news that drowns the American public every day, often leaving people desperate for more information.

    Regarding the Ioannidis viewpoint piece in the Journal of the American Medical Association, this is what was published at the end of the article:

    Conflict of Interest Disclosures: The author has completed and submitted the ICMJE Form for Disclosure of Potential Conflicts of Interest and none were reported.

    Funding/Support: The Meta-Research Innovation Center at Stanford (METRICS) has been funded by the Laura and John Arnold Foundation. The work of Dr Ioannidis is funded by an unrestricted gift from Sue and Bob O’Donnell.

    The ICMJE referenced in that disclosure is the International Committee of Medical Journal Editors.

    I hope this helps.

    Gary Schwitzer
    Publisher, HealthNewsReview.org