Popular blood type diet debunked

Researchers from the University of Toronto (U of T) 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 U of T.

“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, individuals adhering to a diet specific to one’s 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.

3 Reasons To Avoid The Blood-Type Diet

Eat Right For Your Blood Type, a book by Dr. Peter J. D’Adamo, isn’t a nutrition work for Twilight fans. The author’s concept, simply put, is that everyone can and should follow an optimal diet according to whether their blood type is A, B, AB, or O.

It all sounds very scientific, doesn’t it, in a nerd-glasses-and-lab-coat kind of way? You know there’s some 23-year-old actress out there waiting to offer a gushing endorsement of this diet as the cure for everything that ails everyone on Earth.

Indeed, we’re all born with a different set of genetics, which we know contributes to our risk for some diseases and other medical conditions. To eat in a manner that coincides with our genetic makeup, while improving our health? Makes perfect sense, right?

The problem is, unless you recoil from garlic and sleep in a coffin, the so-called blood-type diet kind of, well, sucks.

The good doctor believes that certain foods are good for your blood type, and that others are dangerous. Eat foods from the latter category, and you may experience a variety of health issues, ranging from inflammation and bloating to a slower metabolism and even diseases such as cancer. Or so the book says.


By: Marie Spano

Popular blood type diet debunked The U of T 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.

El-Sohemy says 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. 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.” 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.

So what is the theory?

Prepare to be blinded by science! Dr D’Adamo believes our blood group determines how our bodies deal with different nutrients. His theory is based on the idea that each blood group has its own unique antigen marker (a substance that the body recognises as being alien) and this marker reacts badly with certain foods, leading to all sorts of potential health problems. Furthermore, Dr D’Adamo believes that levels of stomach acidity and digestive enzymes are linked with your blood type. Consequently, he says, by following a diet designed specifically for your blood type, your body digests and absorbs food more efficiently, with the result that you lose weight.

But here’s where the theory becomes even more weird and wonderful. Dr D’Adamo believes that because blood types evolved at different times throughout history, we should eat a diet based on the types of foods our ancestors typically ate at the time when our blood type was first recognised!
When did the blood types evolve?

Blood Group O was the first blood type to be identified, although how we know this is anyone’s guess – we’re talking about our hunter-gatherer ancestors who were around in 50,000 B.C! Nevertheless, Dr D’Adamo believes because our type O ancestors survived and thrived on a high-protein, meat-based diet, that’s the type of diet blood group Os should follow in the 21st century.

Next came the emergence of blood type A, sometime around 15,000 B.C! By this time, our ancestors’ hunter-gathering days were over and instead they started to settle into farming-type communities. The creation of blood type A around this time meant our ancestors did well on a vegetarian-based diet. And again, Dr D’Adamo recommends that blood group A’s should today follow a veggie diet.

Blood type B supposedly evolved around 10,000 B.C thanks to our nomadic ancestors. They left their farms and started wandering the land, constantly moving from place to place. Consequently, Dr D’Adamo’s theory goes, blood group B’s today can get away with eating a varied diet that consists of most foods including meat, dairy, grains and vegetables.

Finally, came blood type AB, which evolved just 1,000 years ago! Dr D’Adamo thinks this blood type helped our ancestors make the transition to modern times. Meaning that people with blood group AB can eat a mixture of the foods suitable for both blood group A and blood group B.


Michael kennedy
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University of Toronto

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