The blood type diet is a diet advocated by Peter D'Adamo and outlined in his book Eat Right 4 Your Type. Its basic premise is that ABO blood type is the most important factor in determining a healthy diet. The diet is widely derided by dieticians, physicians, and nutritional scientists as having no scientific basis.
The cornerstone of his theory is D’Adamo’s premise that lectins in foods react differently with each ABO blood type. Throughout his books he cites the works of various biochemists and glycobiologists who have researched blood groups, claiming or implying that their research supports this theory. In his book, Eat Right 4 Your Type, “Lectins: The Diet Connection”, and in following chapters, lectins which interact with the different ABO type antigens are described as incompatible and harmful, ergo the selection of different foods for A, B, and O types to minimize reactions with these lectins.
D'Adamo groups those thirteen races together by ABO blood group, each type within this group having unique dietary recommendations:
Blood group O is believed by D'Adamo to be the hunter, the earliest human blood group. The diet recommends that these supposedly muscular, active people eat a meat-rich diet along the lines of the Paleolithic diet.
Blood group A is called the cultivator by D'Adamo, who believes it to be a more recently evolved blood type, dating back from the dawn of agriculture. The diet recommends that individuals of blood group A eat a diet emphasizing vegetables and free of red meat, a more vegetarian food intake.
Blood group B is, according to D'Adamo, the nomad, associated with a strong immune system and a flexible digestive system. The blood type diet claims that people of blood type B are the only ones who can thrive on dairy products.
Blood group AB, per D'Adamo, the enigma, the most recently evolved type. In terms of dietary needs, his blood type diet treats this group as an intermediate between blood types A and B.