I've read the book. There is a good amount of research in it and it draws some logical conclusions, some good conclusions, and a whole lot of dumb conclusions. I found it overstates a lot of things and exaggerates many of its claims. It's really a narrow minded, depersonalized, over-simplified, and over-stated set of research backed conclusions that are really not what is always best for one's health.
Aren't designed to eat meat? What? We are omnivores, if we weren't designed to eat meat, we wouldn't be able to. This is an example of an over-simplified and over-stated conclusion, of which there are many in the book. We are genetically/evolutionarily hunter-gatherers, meaning we should be eating meat, nuts, fruits, veggies, whatever is available. Just because we are much better at digesting fruits and veggies than meats does not mean we should not eat meat. We are unable to digest fiber too; should we cut that out of our diets? We only recently attained the enzymes to digest milk; a lot of the population is still lactose intolerant; should we stop drinking milk? The book has some good info in it, but don't read too much into the bull**** they try to sell you.
If you want good health then put the natural healthy foods in, and keep the sugary and over-processed foods out... pretty simple.