If a blood-type diet works for you, it's probably a happy coincidence

by Jennifer Bowden / 25 June, 2018
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Certain blood-type diets are linked to a reduction in cardiometabolic risk factors, but this is completely independent of blood type.

There is no one alive who is youer than you, wrote Dr Seuss. Indeed, you are genetically unique, so should your diet be unique, too?

US naturopath Peter D’Adamo is among those who has offered an answer to that question. He asserted that, because our blood group is associated with the risk of certain health conditions, we should tailor our eating to our blood type.

In his 1996 book Eat Right for Your Type, D’Adamo outlined diets for each of the four blood types with the aim of improving health and reducing the risk of chronic diseases.

D’Adamo’s theory is that those with blood type O would thrive on a diet that resembles the meaty high-protein fare typical of certain groups in the hunter-gatherer era. Type O is considered the ancestral blood type in humans. Those with blood type A would thrive on a vegetarian diet, as this blood type is said to have evolved when humans began cultivating land. Blood type B originated in nomadic tribes, he says, so they would benefit from dairy products. Finally, blood type AB is lumped with a diet midway between that of type A and type B.

Some of D’Adamo’s nutritional recommendations, irrespective of blood type, fit with current nutrition advice, such as advising those with type A to “limit sugar, caffeine and alcohol”.

What’s more, there is substantial evidence that blood type is linked to disease risk. For example, those with type O have a reduced risk of deep vein thrombosis, and type B individuals have a lower risk of type 2 diabetes compared to type O.

In 2010, Scandinavian researchers noted that those with type A had an increased risk of gastric cancer, while peptic ulcer risk was highest among those with type O.

In 2017, a Shanghai cohort study following over 18,000 Chinese men found that people with type B had a statistically lower risk of all cancers than those with type A. This suggests that genetic traits linked to our blood type may play a role in the development of cancers in the gastrointestinal and urinary tracts.

Interestingly, in 2012, researchers noted that blood type seems to modulate the composition of our all-important gut microbiota.

To get to the bottom of whether the blood-type diet uniquely benefits our health, researchers at the University of Toronto analysed data from 1455 participants in the Toronto nutrigenomics and health study. The researchers assessed dietary intake and used a diet score to calculate the similarity of the participants’ diets to each of the four blood-type diets proposed by D’Adamo.

Their findings, published in 2014 in the PLoS One journal, revealed that, irrespective of blood type, those whose diets were most similar to the type A diet had a lower body mass index (a measure of body fat based on height and weight), waist circumference, blood pressure, serum cholesterol, triglycerides and measures of insulin resistance.

Those who stuck to the type AB diet also had lower levels of these biomarkers, with the exception of their BMI and waist circumference.

Those adhering to the type O diet only had lower triglycerides, whereas no significant changes were linked to the type B diet.

However, when they analysed the participants’ results based on their adherence to the diet specifically for their blood type, there was no greater effect on these biomarkers.

In summary, certain blood-type diets are linked to a reduction in cardiometabolic risk factors, but this was completely independent of the individual’s blood type.

So, if you’re following the type A or type AB diet, you might expect to have better health, but that has nothing to do with your blood type and everything to do with the fact that you’re eating more healthily.

This article was first published in the June 2, 2018 issue of the New Zealand Listener.

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