I read the book and tried the diet for a while.

It was convincing since I am a type O and was eating a "healthy" plant-based diet which was making me sick, fat and miserable. I had nothing to lose by trying meat and vegetables. No doubt I felt a thousand percent better and thought there must be something to it. But as soon as it got into type O subtypes and eliminated arbitrary vegetables like cucumbers, I got turned off to it and went on to the next thing. What I took away from it, though, was that my body was much happier eating meat and vegetables than beans and grains.