You'll have to ask Dr Adamo directly about that, I'm afraid I don't know, but I do know that there are many studies which prove specific conditions are linked to blood types. For example, high cancer rates are linked to Blood Type A. Here is one study which shows a positive association between pancreatic cancer and blood type A:
My cousin here beside me is B blood group and has been Lactose intolerant since childhood ..
Plus, to simplify like saying people in such and such a blood group thrive on certain foods is ridiculous imho (not scientific evidence, just practical experience and work) - its not how the body works. Plus, most of the human population dont do well on most grains in general which has been scientifically referenced to on this forum dozens of times over the last 2 years
Why not just look for scientific papers online that proves this diet works?
Oh wait, there are none.
There are certainly plenty of personal experiences I have read where people have improved their health - significantly in some cases - thanks to the blood type diet - so that's good enough for me! ;-)
I read lots of personal testimonies about those rubber bands you put on your wrist to make you all better. They must work!