> Don't forget that it is not easy to remove confounding with smoking, drinking, low physical activity etc. as, incidentally, those who eat most meat happen to also score worse with those factors.

And those who aim to be healthy will probably try to be at least moderate w.r.t their meat intake because they have heard that meat is unhealthy, which further "proves" that meat is unhealthy, while in reality it might be because of other habits that they might have, like exercising.

Things like paleo might make things a little less one-sided.