People around the world are familiar with the blood type diet, a lifestyle plan instructing followers to eat and exercise in certain ways, depending on their blood type. But new research debunks the claims made by creator Peter D'Adamo, suggesting an individual's nutritional needs do not actually vary by blood type.

The study, conducted by researchers from the University of Toronto in Canada, was recently published in the journal PLoS One.

The blood type diet, outlined in a book, suggests different diets for the four blood types, depending at what point in human development the blood type evolved:

  • Type O: this is considered the "ancestral blood group" in humans, so the plan suggests a high-animal-protein diet, typical of the hunter-gatherer period.
  • Type A: this blood type is believed to have evolved when humans settled in agrarian societies, so the plan suggests a vegetarian diet.
  • Type B: this blood group is believed to originate in nomadic tribes, so the plan suggests a high consumption of dairy products.
  • Type AB: the plan recommends a diet similar to that of type B, but there are certain restrictions, for example, only eggs and fish are recommended as sources of meat.

Along with following a specific diet, the book suggests that individuals follow specific exercise routines, in line with their blood type.

For example, people with type O blood are advised to undergo vigorous aerobic exercise each day, whereas those with type A are advised to participate in exercises that encourage mental contemplation, such as hiking, tennis or swimming.

The theory is wildly popular with individuals wanting to boost their health and lose weight. D'Adamo's book - which promises positive health outcomes and decreased risks of chronic diseases, such as cardiovascular disease - was a New York Times best-seller and has been translated into 52 languages.

'No evidence to support diet's theory'

However, the researchers say the link between dietary patterns based on blood type and health outcomes had not yet been examined, which is why they decided to conduct their study.

Examining 1,455 participants who were mostly young and healthy adults, the team collected information about their usual diets, as well as fasting blood samples that were used to determine blood type and cardiometabolic risk factors - insulin, cholesterol and triglycerides.

The researchers also calculated diet scores, based on the food items in D'Adamo's book, in order to determine the participants' adherence to the four blood type diets.

Results showed that there was "no evidence to support the blood type diet theory," says senior author Dr. Ahmed El-Sohemy, assistant professor and Canada Research Chair in Nutrigenomics at the University of Toronto, adding:

"The way an individual responds to any one of these diets has absolutely nothing to do with their blood type and has everything to do with their ability to stick to a sensible vegetarian or low-carbohydrate diet."

Health benefits 'independent of blood types'

Although there was no evidence that eating according to a blood type brings tailored health benefits, the researchers did find that, regardless of blood group, subjects experienced certain benefits.

However, they emphasize that these markers of health were independent of the participants' blood types.

In detail, adherence to each blood type diet yielded associations with the following benefits:

  • Type O: lower serum triglycerides
  • Type A: lower BMI, blood pressure, waist circumference, triglycerides and insulin levels
  • Type B: improved HDL cholesterol levels
  • Type AB: lower blood pressure, serum total cholesterol, triglycerides and insulin levels.
  • El-Sohemy explains that lack of scientific evidence does not necessarily mean the diets did not work:

    "There was just no evidence, one way or the other. It was an intriguing hypothesis so we felt we should put it to the test. We can now be confident in saying that the blood type diet hypothesis is false."

    Other diets have been reported to confer health benefits to followers. For example, a Mediterranean diet has been linked to reduced risk of type 2 diabetes, a longer lifespan and a reduced genetic stroke risk.