Having type O, A, B or AB blood is a feature of each of us that is closely linked to health, especially in cases of emergency, such as an accident, surgery or other problem that requires us to receive a blood transfusion.

Beyond this widely known fact, having a certain blood type determines some aspects of our metabolism and from birth, it establishes what kind of food is best for us. One result of this theory is the so-called blood type diet.

Its mastermind was Dr. Peter J. D�Adamo, who in the early 1980s discovered that not all human blood types emerged at the same time. Rather, some did so before others.

Thus, the variety that exists today stems from changes in people's activities, habits and customs, from their adaptation to their surroundings throughout history and how, as a result of these factors, people's eating habits changed. According to this theory, type O blood was the first to appear, followed by A, B and finally AB.

The planet's first inhabitants, who were basically nomadic meat-eaters, belonged to the first group. When agriculture was discovered and the first permanent settlements emerged, humans with type A blood arose. As man evolved and turned to raising livestock, nourishing himself from their milk, type B blood emerged. The sum of the last two gave rise to type AB blood, the most modern and also one of the least common today.

Blood type has an important role in the body's immune system. So, in an indirect way, choosing foods that do not suit us can weaken our defenses.

All foods have proteins of varying degrees of completeness. Some tend to knock down our defenses if they are not compatible with the characteristics of the proteins. So according to this diet, then, you have to adjust your diet to suit your blood type.

Following the logic of this theory, people with type O blood are predisposed to digesting meat and fish well, and can also handle fruits and vegetables. They do not do as well with grains and cereal. On the other hand, people with type A blood have as their best allies these same grains and cereals, plus vegetables. They should opt for fish rather than meat.

Type B people tolerate dairy products well and can handle meat and fish, but they should avoid grain. Finally, type AB blood, as it is the most evolved and a product of the other three types, allows for a more varied diet so long as you don't overdo it with the meat.

As you can see, grains are among the foods with restrictions, except for the blood types in which they are welcome. They cause different kinds of nutritional intolerance because of the makeup of their proteins and their capacity for destroying the body's cells.

The blood type diet can be efficient and is not harmful so long as you follow it carefully and don't forget to eat all kinds of food at least once in a while. But there are doubts about its premises and in particular, its scientific development and the conclusions it yields.