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Researchers from the University of Toronto have found that the theory behind the popular blood type diet – which claims an individual’s nutritional needs vary by blood type – is not valid. The findings are published this week in PLoS One.

“Based on the data of 1,455 study participants, we found no evidence to support the ‘blood-type’ diet theory,” said the senior author of the study, Dr. Ahmed El-Sohemy, associate professor and Canada Research Chair in Nutrigenomics at the University.

“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,” said El-Sohemy.

Researchers found that the associations they observed between each of the four blood-type (A, B, AB, O) diets and the markers of health are independent of the person’s blood type.

The ‘blood-type’ diet was popularized in the book Eat Right for Your Type, written by naturopath Peter D’Adamo. The theory behind the diet is that the ABO blood type should match the dietary habits of our ancestors and people with different blood types process food differently. According to the theory, people adhering to a diet specific to their blood type can improve health and decrease risk of chronic illness such as cardiovascular disease.

The book was a New York Times best-seller that has been translated into 52 languages and sold over 7 million copies. But last year, a comprehensive review published in the American Journal of Clinical Nutrition found no evidence to support the ‘blood-type’ diet and called for properly designed scientific studies to address it.

“There was just no evidence, one way or the other," said El-Sohemy. "It was an intriguing hypothesis so we felt we should put it to the test."

The ����ֱ�� researchers took an existing population of mostly young and healthy adults who provided detailed information about their usual diets and provided fasting blood that was used to isolate DNA to determine their ABO blood type and the level of cardiometabolic risk factors, such as insulin, cholesterol and triglycerides. Diet scores were calculated based on the food items listed in Eat Right for Your Type to determine relative adherence to each of the four ‘blood-type’ diets.

"We can now be confident in saying that the blood type diet hypothesis is false,” said El-Sohemy.

Michael Kennedy is a writer with University Relations at the University of Toronto.