The Blood Type Diet is pseudoscientific hogwash. The ideas were published in a 1994 book by Peter D'Adamo. While some of his advice may be beneficial, such as avoidance of whey protein or wheat, the logic behind it is entirely fabricated and fraudulent. I will list a few of the bogus claims he makes and you can judge if he knows what he is talking about.
D'Adamo claims that type O is the original blood type in humans, and other types evolved as humans adopted different lifestyles (e.g., pastoral, agricultural). In 1990 “Evolution of Primate ABO Blood Type Genes and Their Homologous Genes,” Saitou and Yamamoto state [p. 405] that type A was the first to evolve in early primates. This happened long before humans even existed, let alone developed agriculture or other lifestyles.
There is no correlation between the blood types found in native populations in the world and their lifestyle. Alaskan Inuit hunter gatherers who have never practiced animal husbandry or agriculture have a higher frequency of Type A blood than Type O. Same for Blackfoot Indians (Niitsítapi) who were nomadic buffalo hunters. On the other hand, Cantonese Chinese who have farmed rice for millenia have more Type O blood than Type A.