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Blood type diet? No evidence for it, and no explanation why it would work

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Does your blood group affect the type of food you should eat? Should you change your diet according to whether you are type A, B, AB or O?

A Facebook post lays out four different diets, claiming each is suitable for people with a specific blood group. “Choose a diet based on your blood type to fight fatigue,” it says.

The post on Healthy First advises people with blood type A to avoid animal-based protein and eat mainly plant protein and some seafood.

People with blood type B should eliminate wheat and corn from their diet, while those with type AB should say goodbye to chicken. People with blood type O should not eat wheat products.

Would this be the healthy thing to do? We checked.

An Indian blood bank official tests a slide covered with a blood sample as he checks a donor's blood group in Salugara Monestry on the outskirts of Siliguri on May 10, 2019. - Some 50 donors as well as monks donated blood due to a shortage on the blood banks. (Photo by DIPTENDU DUTTA / AFP) A blood bank official checks a donor's blood group in India in May 2019. Photo: DIPTENDU DUTTA / AFP)

A Google search for “blood type diet” brings up the website of Dr Peter J D’Adamo, widely recognised for having created the diet.

Throughout your life, you've probably observed that some people tend to lose weight more easily, while for others, their weight is an ongoing battle,” D’Adamo says. “Or wondered why some people are plagued by chronic illness while others stay healthy and vital well into their advanced years.

“Very simply, the answer is in your blood type.

Theory yet to be proven

But the established health websites WebMD, Healthline and Harvard Health Publishing say no research proves the blood type diet works.

A  2014 journal article on the blood type diet by researchers at the University of Toronto’s department of nutrition concluded that while the diet was associated with improved health, this improvement had no relationship to a person’s blood type and so did not support the blood type diet theory.

Dr D’Adamo challenged this study. But his rebuttal acknowledges that the blood type diet theory is yet to be proven. “That the BTD theory is currently unproven by rigorous scientific study is not argued. Hopefully in time this can be rectified by studies which accurately and comprehensively prove or disprove the hypothesis,” he says.

‘Serious questions about why it should work’

But what’s the theory behind the diet?

According to Dr Robert H. Shmerling of Harvard Health, type O “was said to be the original ‘ancestral’ blood type of the earliest humans who were hunter-gatherers, with diets that were high in animal protein”. Blood type A is said to have evolved when humans began to farm, about 10,000 years ago. The group B blood types were “said to arise among nomadic tribes who consumed a lot of dairy products”. And so on.

“Each of these theories has been challenged,” says Harvard Health. “There is evidence that type A was actually the first blood group to evolve in humans, not type O. In addition, there is no proven connection between blood type and digestion.

“So, in addition to a lack of evidence that the diet works, serious questions remain about why it should work in the first place.”

‘Very false information’

Africa Check asked Dr Walter Mwanda, a haematologist at the University of Nairobi’s School of Medicine, if eating according to your blood type was good advice. He was unequivocal.

“That is very false information,” he said. “Forget about it, there’s nothing like that.”

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