Following the publication of the book "Eat Right For Your Type" by Peter J D'Adamo, MD, the Blood Type Diet has become a popular alternative diet that many celebrities have followed.
The theory behind the diet is that you should eat according to your blood type. Type O is the dominant, hunter/caveman type that requires food that is rich in fat and protein, The type A blood appeared later in Western farming cultures, making As more suited to diets heavy on grains and carbohydrates. Blood type B developed with nomadic peoples in Eastern Europe, who relied on herding and the use of dairy products. Blood type AB evolved in relatively recent times from a mingling of groups A and B. Therefore ABs do better on a balance between the A and B type diets.