February 2021

Diet Not Right? What’s Your Blood Type?

Patients are increasingly interested in how their blood type affects their overall health. Today, a lot of this interest is fueled by research linking people with blood type O to a lower risk for COVID-19 infection. But COVID-19 isn’t the only reason patients might ask about blood type – the Blood Type Diet, popularized in the 1990s, is back in the headlines after a recent study debunked its purported benefits. What is the theory behind this diet, and how can you explain this new evidence to patients?

The Blood Type Diet was developed by Peter D’Adamo, ND, and promoted in his 1996 book “Eat Right 4 Your Type.” The diet is based on the theory that blood type affects how the body metabolizes food, and that this is directly related to how we evolved. People with blood type O are claimed to be the original hunters, and therefore should maintain a diet high in animal protein. People with blood type A evolved from the original farmers – they should maintain a vegetarian diet and avoid meat and dairy. Those with blood type B evolved from the original nomads and should eat a balanced diet including meat, vegetables and dairy. People with blood type AB evolved from the mixing of people with blood types A and B. This group should maintain a diet that is mostly vegetarian, and occasionally include meat and fish. But is there anything more than evolutionary theories backing up these recommendations?

Not exactly. While there is some observational data linking certain blood types to risk of certain health conditions, clinical evidence supporting the Blood Type Diet plan is limited. But recently, a secondary analysis of a large clinical trial has been getting a fair amount of press. Patients with obesity were assigned to a strict low-fat vegan diet, similar to the recommendations made for blood type A in the Blood Type Diet. After 16 weeks, there were no differences in cardiovascular outcomes or weight loss between different blood type groups. This contradicts D’Adamo’s theory that only people with type A would benefit from a strict vegetarian diet.

If patients ask about the Blood Type Diet, explain that as long as nutritional needs are met, there isn’t any reason to recommend against it. But it’s important to emphasize that there isn’t any clinical evidence showing that your blood type should dictate your diet. Additionally, the diet requires restrictions that may be difficult for some patients to maintain. Until more research is available, advise patients to focus on healthy lifestyle choices, and point them towards dietary modifications with more supportive clinical evidence, such as the Mediterranean or ketogenic diets.

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