> However, many of the epidemiological studies are over very large populations and time periods, so it's not as though the body of evidence consists of a 6-8 week studies. And honestly the fact that the effects are so strong in such a short period of time strengthen the argument in some ways.
The studies all tell us nothing about the long term implications of diet. The long study tells us nothing because it is purely correlational. The short studies tell us nothing because they are not measuring the thing we care about (long term health outcomes). You can't somehow generate knowledge by combining two types of studies which each are incapable of generating knowledge about the thing we care about.
> I never claimed that meat was bad, only that leafy vegetables were good.
Yeah, I clearly was hallucinating. Nowhere did you mention red meat. And yet I rambled on about it for a paragraph. :-) Sorry!
But:
> I find it almost incredible that your argument against the nutritional value of leafy vegetables is that there aren't enough double blind clinical trials, and then your defense of red meat uses a time correlation that doesn't adjust for any confounding variables at all.
That's because correlation cannot demonstrate causation, but it can demonstrate the lack of causation. It's all about confounding variables, as you point out. If you have two trend lines which correlate, there can always be a third, unmeasured variable which is actually causing the two measured variables. However, if you have trend lines which do not correlate, then the only way they can be related is by some extremely convoluted chain of causation. Which, I guess, is technically possible, but rapidly approaches 0 probability.
In other words, epidemiology is very useful for narrowing the possibly explanations for some phenomena, and it can suggest places where we should continue focusing our attention, but it can't actually tell us if we've found the right culprit.