Health News Review

Physician-blogger Marya Zilberberg, a professor of epidemiology at U-Mass, Amherst, writes,”Unpacking the meat data.” She says a study from Harvard – and news coverage of it – about how red meat is bad for you “deserves some unpacking.” Excerpt:

The investigators examined two large observational cohort studies totaling over 100,000 subjects and tried to estimate the risk of death associated with red meat consumption. Now, first, it has been widely acknowledged that dietary habit surveys are a difficult beast, and that is how these two studies got at the food history. Next, let us look at some of the numerators and denominators. The paper reports 23,926 deaths among these >100,000 subjects over 22 to 28 years of observation. The denominator for this type of a study is person-years, where you simply multiply the number of persons observed by the corresponding number of years of observation. In this instance, this value is 2,960,000 person-years. So, the roughly 24,000 deaths occurred over 2.96 million years of observation, simplifying to 24,000/2,960,000 = 8 deaths per 1,000 years overall. If we were to translate this to an individual’s risk for death over 1 year, it would be 0.008, or under 1%.

The study further reports that at its worst, meat increases this risk by 20% (95% confidence interval 15-24%, for processed meat). If we use this 0.8% risk per year as the baseline, and raise it by 20%, it brings us to 0.96% risk of death per year. Still, below 1%. Need a magnifying glass? Me too. Well, what if it’s closer to the upper limit of the 95% confidence interval, or 24%? The risk still does not quite get up to 1%, but almost. And what if it is closer to the lower limit, 15%? Then we go from 0.8% to 0.92%.

Does this effect size matter, even if statistically significant? What if this were a randomized controlled trial for a statin? What would we say to this result? Even if this is a real signal, which is questionable given the observational design (yes, despite holding a special affection for observational studies, I don’t think that this cause-effect is completely unconfounded; and this matters greatly in view of this minuscule magnitude), I am far more likely to die next time I get into my car than from eating burgers, even if I do indulge in one a couple of times per week.

On Twitter, she highlights this New York Times story as being “way out.”  But an online search suggests they may not be alone:

 

Comments

Elaine Schattner posted on March 13, 2012 at 1:00 pm

Marya and Gary,
I happen to agree with your assessment of this report and the hype about the dangers of eating red meat. Still, a correlation of meat consumption with an increase of deaths at 1% per year, which emerged by analysis of a very large data set, is not trivial. The findings are plausible and, if true, apply to the majority of North Americans. The NCI provides some information on particular compounds in red meat, and how those might be affected by the manner of cooking it, at this page – http://www.cancer.gov/cancertopics/factsheet/Risk/cooked-meats

But – having followed your blogs for some time, I wonder if your personal preferences influence your thinking and choice of studies to dismiss. If you (or I) “like” eating red meat, we might seek to minimize data that points to risks associated. If you or I don’t “want” to find out we have invasive breast cancer, because it involves unpleasant, costly treatments and some risks, we might tend to dismiss data revealing benefits of screening and focus, instead, on reports highlighting limitations.

Just saying,
Elaine

    Gary Schwitzer posted on March 13, 2012 at 1:21 pm

    Elaine,

    I can assure you I have no personal preference about red meat that influences anything I write on the topic – or anything I re-post about what others write on the topic.

    Marya Zilberberg posted on March 13, 2012 at 1:25 pm

    Elaine, what a great comment! Of course, I cannot escape my cognitive biases, but do hope that they are somewhat influenced by data. I think that the issue is not whether or not there is a plausible mechanism, or even whether there is a cause-effect relationship. What I am bothered by in this particular study is the microscopic effect that was inflated to gargantuan proportions in the press echo chamber. What bothers me is that there was no attempt made to say “here is the actual magnitude of potential harm, you decide what to do with it.” Instead, we all ran with the “meat kills” message that sells news.

    The bottom line in the way I think about this stuff is that the best we can do is provide people with the information and give them the tools to interpret such information, so that they can make personal choices. As for healthcare policy, it is a question of trade-offs: how much do we want to spend on ever-diminishing incremental returns? There is not necessarily a uniform answer to this question, but a rational discussions is certainly warranted.

    Again, thanks for calling me out and keeping me honest!
    Marya

Pat Marsh posted on March 13, 2012 at 2:05 pm

Correlation does not equal causation and there are far too many variables not taken in to account including the quality of the meat in the study and when you look at all of the other lifestyle factors associated with the “red meat eaters” including smoking, obesity and lack of physical activity this study doesn’t even qualify as legitimate “research”. More vegan propaganda as far as I can see.

Beth Kitchin, PhD, RD posted on March 19, 2012 at 9:42 am

I was quite disturbed by the poor reporting of this study not just by journalists but by the researchers themselves. Dr. Hu was quoted as stating “the findings are staggering”. the fact that the study is observational and that the data they reported were hazard ratios and not absolute risk didn’t much enter into his comments. I regularly appear on local TV news shows here in Birmingham, AL and do my best to point out the exaggeration of the findings – but I’m afraid my local appearances aren’t going to make a huge difference!

Anoop posted on March 26, 2012 at 10:42 pm

Hi Marya,

Thanks for the nice article!

What is a really a 13% increase or a 1.13 increase in HR? What is an HR number to really show there is a strong effect? Do you have some examples of other HR which showed some strong effects?

And Elaine I didn’t see anything on the link to show that red meat is more affected by cooking than other meats.