Does anyone know the theory (and how proven it is) behind the book "Eat Right 4 Your Type"?

I was perusing through a bookstore the other day and came across a book called "Eat Right 4 Your Type". I was only able to briefly flip through it, but the gist seems to be that there is a particular diet & exercise regimen specific to each blood type. In addition to my first question, I would also like to know if anyone has tried following this diet. (I would especially like to hear from anyone who has tried this who is blood type O+.)