Probably worthy of its own thread, but the takeaway I have from "Forks Over Knives" (and a pretty fair exposure to the several principals behind this way of thinking) is basically along these lines:
-There is very strong evidence that a diet heavy in meat and dairy creates a much stronger opportunity for heart disease in its many forms, at least many types of cancer, and a number of other diseases. There is a great deal more to the "plant based, whole foods" dietary approach than just losing weight.
-The strongest evidence, it seems to me, is that casein (a protein found in dairy products) in particular is a pretty serious hazard. I happen to agree that there's some degree of unwarranted interpolation from casein to other animal-based proteins or diets. But I also dissent from any judgment that this possibly premature set of conclusions are inherently wrong because of the zeal some people obviously have behind them.
-The data set from the so-called "China Study" (a long term study of health and nutrition conducted across China starting in the 1970s) leads in a number of sometimes conflicting directions, and this is not a shock, but there are a pretty substantial number of very, very strong correlations that point in the same direction -- the availability and consumption of animal products in the diet is a strong indicator of the prevalence of a wide variety of serious long term diseases. There truly are case after case of afflictions that are widespread in more affluent areas and are virtually absent in poorer areas (whose citizens eat far fewer animal products, but are genetically inseparable from the others).
-Beyond the highest profile studies and the cross-national scatterplots, there are really scary tidibits that point very directly to us (the public) really not getting it right on this sort of thing. For most of my life, I've been under the impression that the heart disease in my family is just a tough hand I've been dealt, and that I am likely on a progression toward real problems there (understanding that my lifestyle choices play some role, but figuring a life with heavy medication is in my present and future no matter what). Then you learn that autopsies in youngish Americans who die of unrelated causes already show early signs of heart disease... while autopsies of people from non-animal-eating cultures show essentially *none* of these signs at any age. Great pithy statement for the debate: if you're a cardiologist and you move out into rural china where nobody eats much meat, milk, or butter... you're basically going to have to sell pencils for a living, you're not going to have anything to do.
-Probably the single most consolidated fact that is deeply hard to dispute is this one: nutritionally speaking, there's basically nothing you get from eating animal products that isn't better for you coming from plants. Yes, a completely plant-based diet may require some vitamin B12 or other modest supplements, but all in all, there's really no contest at all, and virtually everyone acknowledges this.
-Amidst all this, I think the healthful effects of a much-reduced consumption of animal proteins, especially dairy, is very strongly supported. What I don't see enough clear evidence for is the health-driven necessity of going to absolute zero. The most powerful changes seem to take place when going from "high animal" to "low animal" content in the diet. This isn't as thrilling to the animal rights side of the debate, who really really want to have strong science behind their pre-existing viewpoint... but thus far there doesn't seem to be a powerful case (to me) that an absolute vegan diet is separable from one where, say, 5% of your calories come from animal proteins (still far lower than our standard diet here, of course).
-There's a quandary in the medical and scientific and regulatory communities over what to do about this. Do you advise people that they should make seemingly radical changes to diet and lifestyle? Or do you try to get them to make less drastic changes that are admittedly more likely to take root? (This takes the shape of a doctor-patient conversation, all the way up to the development of the national "food pyramid" guidelines) I think I depart from many of the true believers on these matters in acknowledging this is a legitimately tough call in many ways.
-Politics of health care subsidies set aside for the moment, it's an almost scary notion that there might well be a fairly simple, readily/universally available, and practically dirt-cheap means to very nearly wipe out heart disease, and to at least substantially (if not massively) deplete the prevalence of many cancers and long-term diseases like diabetes, asthma, rheumatoid arthritis, and the like. Not a way to do it in Sweden or in rural China in the 70s, but right here and right now.
I think it's a very intriguing area of exploration right now. And all told, I think there's a significant chance that what our society saw with smoking over the last 30-40 years could happen next to animal consumption, at least in part.