Blood type diet
The Blood type diet is a type of fad diet that claims that your blood type affects how you digest different kinds of food, and thus what you should eat is determined by your blood type. This is based on the idea that your blood type is linked to your genotype, and that A type blood, for example, is linked to reduced ability to digest meat.
The diet was founded by Peter D'Adamo (a naturopathic doctor) and published under the catchy-titled Eat Right 4 Your Type. It was founded based on the evolutionary theory of blood type. Although the diet ignores factors such as Rhesus negative/positive and other rarer sub-types, D'Adamo claims that 90% of the properties of the blood are due to the ABO groups.
There are four primary blood groups in the ABO system. Types A, B, AB and O. For each group, a different diet is recommended for healthy living.
- Blood group O: The Hunter; stated to be the earliest human blood group. D'Adamo recommends a higher protein intake for people of this type.
- Blood group A: The Cultivator; claimed to be a more recent blood type that has evolved since agriculture. As a result, the diet claims group A people should avoid meat and consume vegetables instead.
- Blood group B: The Nomad; D'Adamo claims that people with group B blood can indeed thrive on dairy products due to it being associated with a healthy and highly evolved immune system.
- Blood group AB: The Enigma; As a combination of types A and B, it is considered the most recently evolved blood type. As a result Eat Right 4 Your Type suggests a diet part way between that of A and B.
 The bullshit
While it is certainly true that genetics plays a part in what humans can effectively digest and that blood type is also dependent on genetics, correllating the two is as dubious as linking metabolic rate to hair colour. One of the central aspects of the diet claims that lectins in food react differently depending on blood-type, something currently not backed up by any biochemical research.
There is also a considerable lack of genuine clinical trials testing the diet, despite multiple claims by D'Adamo to the contrary. His own trial, which has apparently lasted 10 years, still has not been published - so the results he claims cannot be taken as true at all. Indeed his unwillingness to publish is an indication that the trial has either shown a negative result, was methodologically flawed or possibly outright fraudulent. The only evidence he has properly presented was a survey on his website, saying that about 70% of people thought it worked. However, self-reported "data" like this aren't considered valid by academic standards.