my mom has been following eat right for your type diet for a few years now and she feels awesome. she lost weight, her headaches went away, she had more energy, she used to be super constipated all the time, now she's super regular. i think it has validity. i am the same blood type as she is, so she tells me all the time what and what not to eat. i dont listen for the most part, but pre-contest i listen to her just in case she's right - there's no room for error when you're pre-contest. haha.
it is true that i feel worse when i eat certain things that im not supposed to according to the blood type diet. doctors dont ALWAYS know everything. imo lots of doctors prescribe an expensive medication instead at looking at what else could help - like natural supplements or diet. i say try that diet out for a month, see how you feel.