"But, allow me to finish with a suggestion. All of these diet doctors- including McDougall, Barnard, and Esselstyn from the veggie side, and Eades, Cordain, and Mercola from the paleo side- they should all agree to undergo a carotid artery ultrasound at the same time so that we can find out the condition of their carotid arteries and compare. The test is harmless, and it’s not that expensive. And it tells a lot about a person's real internal health. The only caveat is that age is a factor as arteries tend to worsen with age. So, an adjustment would have to be made for that. However, some of the above-named doctors are close in age (60-ish), so a straight-up comparison would be fine. I am 60, so let me be the first to volunteer. I’ll do it; I’ll pay for it: and I’ll share the results with the world. Doctors, are you willing?"Wouldn't I savor the results of that comparison. You could say it isn't valid, that n is too small, that their results are testimonials and not statistically relevant. Certainly every body is unique. I think you'd have to account for non-dietary factors like physical activity and environmental pollutants ... and age as Dr. Cinque pointed out.
There is something else ... the aspect of generalizability. That is, if you find that one diet is better than another, can you apply those results to a population that differs from your test population. In this case, can you apply that diet to a person who is not male, not (mostly) Caucasian, and who does not possess an income and support network which fosters the diet. I'm not poo-pooing the idea. I'm just thinking out loud. It would be a provocative little data point, one I would relish.