publication date: Oct. 4, 2019
Conversation with The Cancer Letter
Guyatt: Existing dietary guidelines for red and processed meat are based on slim evidence and are paternalistic
Department of Clinical Epidemiology and Biostatistics,
The senior author of the recent recommendation that disagrees with the dietary guidelines promulgated by mainstream health organizations said there is low-certainty evidence of increased risk of cancer, heart disease, and other harm from eating red meat and processed meat.
The Cancer Letter’s coverage of the paper is available here.
“There is low-quality evidence of a small effect. To us, it is presumptuous and paternalistic to tell people, on the basis of low-quality evidence of small effects, that they should cut down on eating their red meat,” said Gordon Guyatt, distinguished professor at the Department of Clinical Epidemiology and Biostatistics at McMaster University.
“Some people may well, on the basis of that evidence, choose to do so, but we think a majority of people would not. And it’s hard to imagine anybody claiming that all or almost everybody, on the basis of low-quality evidence of small effects, given people’s quality of life enhancement when they eat meat, that everybody would choose to cut down their stuff.”
Guyatt, the scientist credited with coining the term “evidence-based medicine,” said no mainstream health organizations have contacted him directly after his group’s paper was published in the Annals of Internal Medicine.
“From what I understand—which I mainly heard secondhand from the porch, from my colleagues—the organizations that have previously said, ‘Death awaits you if you continue to eat red meat,’ have not been terribly positive,” Guyatt said.
Guyatt spoke with Matthew Ong and Alex Carolan, reporters with The Cancer Letter.
So, doctor, may I have a smoked kielbasa tonight? How about a hamburger?
That is a matter of your values and preferences. So, the situation is that there is low-quality evidence suggesting that your hamburgers may, if you continue to eat them on a daily basis or regularly, increase your risk of cancer and increase your risk of cardiovascular disease.
But if it does increase it, and it may not, because the evidence is only low-quality, the increase will be a very small increase. So, it’s up to you. How much does the hamburger appeal to you and how much are you ready to give up to avoid a small and uncertain harm?
And the same applies to the kielbasa?
So, what led you and your team to perform these studies?
Well, one of the gentlemen who did a postdoctoral fellowship with me, Brad Johnston, now works out of Halifax, and I continue to collaborate with him.
He has taken a career direction where he wants to focus on nutrition, and particularly on nutritional guidelines, having noted that many nutritional guidelines are not high-quality, and are quite flawed, and trust me, the guidelines are necessary.
I continue to collaborate with him, and he has asked me to be part of his team, having decided to take on red and processed meat as the first of his nutritional guidelines.
Are you planning on conducting systematic reviews of all major nutritional and dietary guidelines going forward?
Well, I don’t know if we’ll ever get to all of them. However, we are currently planning our next project, which has to do with fats.
Could you briefly describe your findings from your systematic reviews? Also, why are these findings important to public health?
So, what our findings suggested is that there is only low-quality evidence available linking red and processed meat with cancer and cardiovascular outcomes.
However, that low-quality evidence does suggest a possible causal connection between meat consumption and cancer and cardiovascular risk.
However, even if there is a true causal relationship, and there may not be, the impact over a lifetime would be quite small of continuing to eat red meat. That is, the health adverse outcomes will occur very infrequently.
To put it the other way around, decreasing your red meat, even if the causal connection is true, and it may not be, would lead to only a small reduction in risk.
Anything that might have an impact across the population—clearly, everybody has to eat, and, clearly, lots of people eat red meat—so, anything that is an issue across the whole population or influences a whole population may be relevant for public health.
I noticed that everyone who participated disclosed how much meat they eat a week, and I think I saw that you are a pescetarian.
Yes. That is correct. So, to clarify that, I am not a pescetarian for health reasons. I am a pescetarian because of animal welfare and environmental reasons. And maybe I shouldn’t even be eating fish, but I still do.
Could you walk us through the methodology for your studies?
So, over the last 20 years, there have been standards for doing what we call trustworthy guidelines. And the standards include who you have on the panel.
So, nowadays, you’d like to include, as we did, people who are expert in nutrition, people who are expert in interpreting the literature—we call them methodologists, people like me—and patients, if it’s a medical condition; in this case, people from the community. So, we included all of those groups in our panel.
Second, trustworthy guidelines demand minimizing conflict of interest. So, nobody on our panel had any financial conflict of interest and we minimized intellectual conflicts of interest. And since some people might perceive what you’re eating as a conflict of interest, we declared, as you have noted, the meat in our diet.
A third element of trustworthy guidelines is up-to-date systematic reviews of the best evidence. So, we conducted what we believe is often state-of-the-art methodology in conducting systematic reviews of red and processed meat for cancer, red and processed meat for cardiovascular disease, dietary patterns and cancer and cardiovascular disease, and those were all observational studies, reviews.
We also did a systematic review on the randomized trials that have addressed the potential impact of meat consumption on health outcomes.
And finally, since this is, we believe, a value and preference-sensitive decision about meat, we conducted a systematic review of studies that had addressed people’s values and preferences with respect to meat consumption. So, those five systematic reviews—hopefully, we believe, done under the most rigorous, up-to-date standards—informed the guideline.
Some critics say that the meta-analyses place more weight on results from randomized trials, over that of observational studies, which was how your team derived the published conclusions.
Untrue. We concluded that the randomized trials also only provide us with low-quality evidence.
The randomized trials suggested there is no relationship between red and processed meat and health outcomes. In fact, when we presented our summaries and our best estimates of the magnitude of effect—as it turns out, a very small magnitude of effect—we based those on the observational studies.
Others have said that it would have been important for you to make conclusions for red meat and processed meat separately. Could you respond to that as well?
We did. If you look at our summaries, he makes separate summaries for red and processed meat. The magnitude of the associations were consistently a little bit higher with processed than with red meat.
Some experts say that they are a little suspicious of these recommendations, because some authors on your team published an article two years ago, concluding that eating more sugar is fine, and received funding from food companies, according to critics. Is this true?
First of all, and the statement was not that eating sugar was fine. I should say I was not a coauthor on that paper, but I was acknowledged, because I gave them advice, so I know what was in it. It was that the guidelines were flawed, which are two very different things.
Second, the only person with overlap in the two projects was Brad Johnston, who has not taken anything that would constitute a conflict of interest in this one.
I don’t know when Brad took the money from this group that has all sorts of food makers in it, but it was more than three years ago. The conflict of interest about funding is accurate for the stated time period. I think Brad reported his conflict of interest.
I think Brad told me that there was somebody in his group who did not. As I say, I only gave them some advice in it. But anyway, you’d either have to talk to Brad or look back at the paper.
What I can say with confidence is that our reports have no conflict of interest in the current situation.
You mentioned that the guidelines on consumption of sugar were flawed. Could you briefly describe the framework for that?
Once again, I was not an author in the paper. With all those limitations, typically they would not have done a comprehensive search.
They would not have followed the most rigorous guidelines. In particular, they would not have used grade, and they would have paid little attention to people’s values and preferences. They would not have summarized their results in summary findings, tables, or evidence profiles.
Now that, frankly, is not by my memory. This is just what I would’ve expected, because then these are the limitations that have tended to be the case in nutrition guidelines.
So, it appears many of our readers are not familiar with NutriRECS. What is NutriRECS, and what is your business model? Also how is the organization funded?
If you Google NutriRECS, you can find out all you want to know about the group. Our business model is the usual academic model—get your work done by hook or by crook, volunteer labor of folks working for an education and their names on prominent papers, graduate students whose work will be part of their dissertations, and visiting scholars and professors who come to learn how we do things and how to get publications in top journals (Miah Han on the red meat and cancer paper is a good example of the last of these).
If Brad has managed to get some funding specific to NutriRECS, I haven’t heard. So, it’s effectively in-kind funding from the universities that pay our salary to do this work, and the sources above (sometimes, we get grants to pay grad students’ salaries).
Your team’s recommendation, as it appears, is that everyone should continue consuming red meat and processed meat at current levels. Please correct me if I am mistaken.
First of all, a slight misstatement in what you said. We did not say everybody should continue their red and processed meat consumption.
We said that it should be an informed decision, and our guess is that the majority of people who were fully informed of the evidence would choose to continue their red and processed meat consumption, but that a minority—perhaps a sizeable minority—when fully informed would choose to reduce.
So, we’re not telling you that everybody should continue. We’re saying that it should be a fully informed decision, and our guess is that, when fully informed, the majority of people would choose to continue. We could be wrong.
Perhaps the majority of people would choose to reduce. But that was our guess, that the majority would choose to continue. And that’s why we made that weak recommendation. So, that’s the slight correction from the way you put it.
If the evidence is of low certainty, if the magnitude of effect is small, and if the absolute risk is low, do you consider the evidence sufficient for informing guidelines?
Well, you have to make choices; right? People either choose to eat red meat, increase their red meat, decrease their red meat, whatever. Okay?
And I’ll make a little parody of evidence-based medicine, which we try to put into practice.
A patient comes to see the physician and says, “Oh, I got this problem. Doctor, can you help me?”
Doctor turns to the computer, spends a few minutes on the computer, turns to the patient and says, “Sorry, I can’t help you. No randomized trials.”
That is not evidence-based medicine. So, evidence-based medicine is using the best available evidence to make decisions, because you need to make decisions. And the same is true here.
This is certainly not ideal to have only low-quality evidence, but people need to make decisions about their red meat consumption, and the decisions should be based on the best evidence that is available.
Unfortunately, in this case it’s only low-quality, but we should look at the best evidence available and, considering the limited quality, make our decisions accordingly.
I see that you’re credited with coining the phrase “evidence-based medicine.” What’s the story?
Well, in 1990, I took over the residency program in internal medicine at McMaster University in Hamilton.
And we had a basic notion of what we wanted to do, which is that we wanted to train a new breed of physician who would pay much closer attention to the evidence, would have a much deeper understanding of the nature of medical evidence and use that to optimally manage their patients.
And we wanted to attract people to McMaster who might be interested in that approach. And the approach needed a name.
So, my first go at coming up with a name was “scientific medicine,” which so outraged my colleagues that I decided I’d better go back to the drawing board.
And my second choice was “evidence-based medicine,” which ended up being extremely popular.
What sorts of responses have you received so far to your team’s papers from mainstream health organizations?
Well, no mainstream organizations have contacted me directly.
From what I understand—which I mainly heard secondhand from the porch, from my colleagues—the organizations that have previously said, “Death awaits you if you continue to eat red meat,” have not been terribly positive.
You’ve addressed some of the following, but I want to make sure to condense it. The statements I’ve received in response to your recommendations appear to range from A) the totality and preponderance of evidence gathered so far continue to point to the importance of limiting or reducing consumption, to B) these systematic reviews show that there is insufficient evidence to inform guidelines, so the investigators should be saying “We don’t know.” What is your response to both of these statements?
With respect to the first one, we disagree. So, there is low-quality evidence of a small effect.
To us, it is presumptuous and paternalistic to tell people, on the basis of low-quality evidence of small effects, that they should cut down on eating their red meat.
Some people may well, on the basis of that evidence, choose to do so, but we think a majority of people would not.
And it’s hard to imagine anybody claiming that all or almost everybody, on the basis of low-quality evidence of small effects, given people’s quality of life enhancement when they eat meat, that everybody would choose to cut down their stuff.
So, the first is a mischaracterization of the evidence and, in my personal view, a paternalistic or parental approach.
Instead of giving people the evidence and letting them make their decisions, telling them what to do on the basis of this evidence, to me is quite problematic.
With respect to the second statement, you’re quite right. That’s what I just dealt with. It would be absolutely wrong for doctors to say, “Oh sorry, not enough evidence. Can’t advise you.”
As a matter of fact, most of what we do in medicine, sadly enough, is still low-quality evidence. And that goes back to the parody of evidence-based medicine that I just gave you.
We don’t say, “No, sorry. No randomized trials, can’t help you.” Instead, we use the best evidence available. And, in my opinion, it is quite informative to tell a person who is inquiring, “Oh sorry, we only have low quality evidence that red and processed meat may be causing increases in cancer and cardiovascular risk, but it may not. We’re not sure. And if it does, the increases in risk are small.” That strikes me as very informative.
I believe our sources so far appear to agree that number one, your findings in these systematic reviews are in line with existing evidence, in the sense that yes, it is low-quality evidence, but nevertheless, there is an association between consumption and adverse health outcomes. And number two, certainly, that there is no positive recommendation, based on the evidence, to increase consumption. Are these statements accurate?
Those are both accurate. The only qualification would be, although we and other people focused on the observational studies—they’re limited, but one should perhaps not dismiss completely the randomized trials, which suggest no association.