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The theory behind another fad diet has been debunked.

The popular blood type diet, which claims an individual’s nutritional needs vary by blood type, is not valid, according to a new study.

Food scientists say that doesn’t mean the diet doesn’t work. It’s just that the idea upon which it is based isn’t correct.

The diet was popularised in the 1997 book Eat Right for Your Type, a New York Times best seller by naturopath Peter D’Adamo. More than 7 million copies have been sold.

Ahmed El-Sohemy, Associate Professor and Canada Research Chair in Nutrigenomics at the University of Toronto, says there’s no evidence to support the diet.

“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 Dr 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 theory behind the diet is that the blood type should match the dietary habits of our ancestors and people with different blood types process food differently.

According to the theory, individuals adhering to a diet specific to one’s blood type can improve health and decrease risk of chronic illness such as cardiovascular disease.

For example, a higher protein diet is recommended for blood group O and mainly vegetables for group A.

The researchers took 1,455 mostly young and healthy adults who provided detailed information about their usual diets and provided fasting blood that was used to isolate DNA, determine their blood type and the level of 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.

El-Sohemy said that a previous lack of scientific evidence doesn’t mean the diets didn’t work.

“There was just no evidence, one way or the other,” he said. “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.”

The results of the University of Toronto study were published today in the journal PLoS One.

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.

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