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Wednesday, April 25, 2012

Meat (an example of "correlation does not equal causation")

Meat, particularly red meat has gotten quite the bad rap for a long time.

Many epidemiological studies (those that study factors and disease distribution in populations) have revealed correlations between red meat consumption and various chronic diseases, most notably cardiovascular disease.

Red meat consumption and risk of heart failure in male physicians.

Red and processed meat consumption and risk of incident coronary heart disease, stroke, and diabetes mellitus: a systematic review and meta-analysis.

Associations of processed meat and unprocessed red meat intake with incident diabetes: the Strong Heart Family Study.

However, there is a huge caveat here in that these studies were PURELY OBSERVATIONAL. Factor A went up at the same time Factor B went up. We CANNOT conclude that Factor A caused Factor B to increase, or vice versa. There very well could be a Factor C which causes both to increase, or some other complex interactions of factor.

The point is, observational studies are good for coming up with ideas about where to direct research, but are NOT for drawing conclusions from. Observational studies reveal trends, which must be followed up with experimental studies in order to draw any substantive conclusions.

Now, what kind of results DO experimental studies show?

Incorporation of lean red meat into a National Cholesterol Education Program Step I diet: a long-term, randomized clinical trial in free-living persons with hypercholesterolemia.

Increased Fat-Free Body Mass and No Adverse Effects on Blood Lipid Concentrations 4 Weeks after Additional Meat Consumption in Comparison with an Exclusion of Meat in the Diet of Young Healthy Women

Now, there are still a few studies out there, experimental studies, that show some increases in risk factors for certain diseases. But then again, we must ask, what are "risk factors"? More correlations!

In some circumstances, we are sure enough about the mechanisms of diseases to actually get something from correlations, however many times, this is not the case.

I don't have time to go into the nuances of this subject, so I will leave you with someone who has gone over this topic quite well.

The Meaty Gritty on the Red Meat Debate: A Comprehensive Rebuttal of the Constant Assault On My Beloved Steaks