In the journals: Blood-type fad diet theory fails a test
Special diets tailored to a person's blood type produced no health benefits, according to a study in PLoS ONE. The research tested the highly dubious idea that certain diets match up to blood types based on when those blood types first evolved. For example, people with type O blood types would supposedly thrive best on diets rich in animal protein because type O evolved when our ancestors were hunter gatherers.
Is this pure pseudoscience? To test that, researchers carefully assessed the diets of more than 1,400 people to determine how closely their eating style matched their purported blood-type diets — type O, type A, type B, or type AB. Researchers also graded the participants on various standard markers for health, including body mass index (a measure of obesity), blood pressure, cholesterol, triglycerides, and blood insulin levels.
In the end, the researchers could find no evidence that sticking to one's blood-type diet was associated with better health. Of course, the lack of proof for a link doesn't prove there isn't one, but it certainly didn't show up in this study.