Blood type diet

The blood type diets are fad diets advocated by several authors, the most prominent of which is Peter J. D'Adamo. These diets are based on the notion that ABO blood type is the most important factor in determining a healthy diet and each recommends distinct diets for each blood type.

The consensus among dietitians, physicians, and scientists is that these diets are unsupported by scientific evidence.

The underlying hypothesis of blood type diets is that people with different blood types digest lectins differently, and that if people eat food that is not compatible with their blood type, they will experience many health problems. On the other hand, if a person eats food that is compatible, they will be healthier.

That hypothesis is, in turn, based on an assumption that each blood type represents a different evolutionary heritage. "Based on the ‘Blood-Type’ diet theory, group O is considered the ancestral blood group in humans so their optimal diet should resemble the high animal protein diets typical of the hunter-gatherer era. In contrast, those with group A should thrive on a vegetarian diet as this blood group was believed to have evolved when humans settled down into agrarian societies. Following the same rationale, individuals with blood group B are considered to benefit from consumption of dairy products because this blood group was believed to originate in nomadic tribes. Finally, individuals with an AB blood group are believed to benefit from a diet that is intermediate to those proposed for group A and group B."

As of 2013 there is no scientific evidence to support the blood type diet hypothesis and no clinical evidence that it improves health. Peter J. D'Adamo is the most prominent proponent of blood type diets.

Luiz C. de Mattos and Haroldo W. Moreira point out that assertions made by proponents of blood type diets that the O blood type was the first human blood type requires that the O gene have evolved before the A and B genes in the ABO locus;phylogenetic networks of human and non-human ABO alleles show that the A gene was the first to evolve. They argue that it would be extraordinary, from the perspective of evolution, for normal genes (those for types A and B) to have evolved from abnormal genes (for type O).

Yamamoto et al. further note: "Although the O blood type is common in all populations around the world, there is no evidence that the O gene represents the ancestral gene at the ABO locus. Nor is it reasonable to suppose that a defective gene would arise spontaneously and then evolve into normal genes.

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