Friday, January 28, 2011

Women, Red Meat, And Stroke Risk

My doctor sent me a link to this study:

Does Red Meat Consumption Raise Stroke Risk [In Women]?

We've discussed my diet change, and exchanged thoughts and emails about it.  It's nice to know that he's concerned enough to send me stuff like this, even though he does apparently refer to me as "Caveman" now (some of my friends are also his patients).  But who can blame him?  First running in toe shoes, and now the Paleo diet...  If the shoe fits, wear it.

Am I concerned about this news?  Not really, and here's why:

"Comment: These results agree with those from the Nurses' Health Study, in which women who consumed [greater than or equal to]1 serving of red or processed meat daily were at excess risk for ischemic stroke (as well as hormone receptor-positive breast cancer [JW Womens Health Jan 11 2007])."

Tom Naughton has a great post titled "Meaningless Associations":

"Perhaps you recall the estrogen fiasco. Examining data from the Harvard Nurses Study [aka the Nurses Health Study], researchers found that post-menopausal nurses who took estrogen had a lower rate of heart disease. Based on that finding, doctors were ready to start prescribing estrogen to every middle-aged women in the country. Just one little problem: when estrogen was tested in a controlled clinical study, the women who took it ended up with a higher rate of heart disease, not lower. Same thing happened in a clinical study with men.

"As it turned out, the nurses who took estrogen were simply more health-conscious than most other nurses and were taking estrogen because they believed it was good for them — not because it actually was (at least for heart health). Health-conscious people are different. They exercise more, eat less sugar and other junk food, make sure they get enough sleep, take their vitamins, are less likely to smoke or drink alcohol to excess, and more likely to see a doctor if something doesn’t seem quite right with their health. Estrogen wasn’t making nurses healthy … healthy nurses were taking estrogen."

In other words, just because an epidemiological study shows that X is associated with Y doesn't really tell you anything.  If fact, you may find out, as in the case above, that what is going on is exactly the reverse of what you might think. 

Next, we have this:

"One limitation of this study is that constant consumption of red and processed meat for 10 years was assumed (diet was only ascertained once)."

That's one heck of a big assumption.  It pretty much means that this is a wild guess, with a tenuous attachment to reality.

But what do I know: I'm not a doctor, or a scientist, nor do I have any specific expertise...  Fortunately, people like that exist, have web sites, and have looked at this study:

"'This study is an observational study that relies on dietary recall, which is a notoriously unreliable parameter. Further, the ‘42 percent increased risk,’ while making for a good headline zealously exploited in simplistic reporting, makes me wish yet again that epidemiologists would be a little more honest so that unless they observe a relative risk in such a study of at least double, perhaps they should not bother reporting it. As long as data dredging like this is published by allegedly respectable journals, we can’t blame reporters for jumping on it.'

"The study, like so many lacking proper controls, presents an array of problems with regard to confounding variables and the problem of separating cause and effect.

"The media has capitalized on the research, however, because 'it fits in with the popular wisdom that red meat is bad, and the less of it you eat, the healthier you are,' says ACSH’s Dr. Elizabeth Whelan. 'Other retrospective analyses have demonstrated that red meat actually has no effect on stroke risk, yet they get thrown down the epidemiology garbage chute because it doesn’t create nearly as big of a media splash.'

Don at Primal Wisdom also looked at this study recently:

"Thus, we know that the absolute incidence of cerebral infarction in the low meat group was not more than 4%, and conclude that in the high meat group not more than 5% of subjects had a cerebral infarction type stroke--which means that more than 95% of women eating the so-called high meat diets (more than 3 ounces daily) did not have a stroke. The absolute difference between the two groups was not more than 1%, but by using relative risk, the authors get to report it as a 22% increase in risk. Creative accounting."

A one percent difference in a study like this is pretty much noise.

But here's the meat of his post (pun most definitely intended):

"Now take a close look at the last sentence of the abstract of the journal article:

"Fresh (unprocessed) meat consumption was not associated with total stroke or with any stroke subtype."

"What? In the immediately previous sentence, they stated that red meat was associated with a 22% relative risk in cerebral infarction type stroke, but the last sentence says that fresh meat was not associated with total stroke or any subtype, which would include cerebral infarction.

"I feel confused. How can "high" red meat consumption be associated with a 22% greater risk of stroke, and yet not associated at all with total stroke or any stroke subtype? It seems that the trick must be in combining both fresh and processed red meat to get the positive association.

So the final conclusion of that original link:

"Nonetheless, these results show that even healthy, nonsmoking women can lower their stroke risk by cutting back on red meat intake; clinicians should consider inquiring about the dietary habits of all their patients."

Is entirely bogus.  The results show nothing at all, in fact, except that the scientific establishment and the media are to be treated as one would any other source of information: with extreme scepticism.

Caveat Emptor.

Ladies, start cutting your steaks...