I tried this diet some months ago - my friend is Group 0 and devoted to it -- not for weight loss, but health, she believes it is right for her. ( regarding arthritis, etc.) As an 0, she has increased meats, etc and as a vegetarian she has found this a challenge. But ( not surprisingly to me) she feels better for it.
On the other hand, I as a group A, should eat .... wait for it......high carb, mostly vegetarian, lotsa pulses, rice etc. I managed 2 weeks and felt half dead. seriously, not well at all. Reading the book was interesting though and we all have to find our own way. There is a website you can find through Google.
My opinion ? Possibly ok if youre group 0 and therefore very meat orientated. as a group A...... well.......forget it !!!! I could not possibly try it again.