The Blood Type Diet


I am often asked whether blood type diets are a thing. Each year there’s a new popular diet on social media platforms, promoting fast drastic weight loss, however much like many other fad diets, the blood type diet lacks scientific evidence and I’ve gathered the research to make you understand why.

The blood type diet is based on the theory that your blood type determines what you should and should not eat. The theory is that eating foods that are compatible with your blood type will help you achieve better health outcomes. This theory gained its popularity in the 60’s when Peter D’Adamo, a naturopathic physician, wrote a book called “Eat Right 4 Your Type”.

D’Adamo’s theory, states that people with blood type A should eat a vegetarian diet that is high in fruits and vegetables and low in meat and dairy. People with blood type B should eat a diet that includes meat, poultry, fish, and dairy, but should avoid wheat and other grains. People with blood type AB should eat a diet that is a mix of both the A and B diets. People with blood type O should eat a diet that is high in protein and low in carbohydrate and stay clear of dairy, grains and legumes.

However, D’Adamo failed to back these claims and the theory has been debunked by the scientific community due to a lack of evidence supporting the idea that your blood type has anything to do with how your body processes food.

So what does research state about blood type diets and how has D’Adamo’s theory been debunked?

There are four main blood types: A, B, AB, and O.

Each blood type is determined by the presence or absence of certain antigens (proteins) on the surface of red blood cells.

  • Type A has the A antigen
  • Type B has the B antigen
  • Type AB has both the A and B antigens
  • Type O has neither the A nor B antigens

When looking at variations across blood types, studies have shown that individuals with blood type A have a higher risk of cardiovascular disease when compared to other blood groups. Whereas Blood type O individuals were found to have a higher frequency of increased body weight when compared to other blood types. Chinese researchers looking at COVID-19 have also found increased odds of contracting COVID-19 in blood type A individuals.

Now considering the increased risks found to be associated with blood type A and O, it makes sense for D’Adamo’s theory to suggest individuals with a higher cardiovascular risk to eat more vegetables and fruits and avoid meats and dairy that are high in saturated fats. As it would also make sense to ask individuals with blood type O to lower their intake of carbs and increase protein to avoid weight gain.

Therefore, to investigate this theory, Dr. Neil Barnard, founder of the Physicians Committee for Responsible Medicine, and his team of researchers posed the following scenario;

If D’Adamo’s theory were to be true, if you were to place an individual with Blood type A diet and blood type O diet on the same plant-based diet, those having blood type A would do significantly better than those with blood type O (meat-eaters).

This was found to be untrue, since both blood types experienced significant weight loss after 16-weeks of diet intervention with an average body weight change of –5.7 kg for blood type A participants and –7.1 kg for type O participants. Moreover, after 16 weeks following a low-fat vegan diet,all blood types improved their overall LDL cholesterol and fasting glucose levels on a plant-based diet.

Plant Based Diet

So whether you are blood type A, O or any other, the best way to be healthy is to eat a balanced diet that includes plenty of fruits, vegetables, whole grains, and lean protein as all individuals benefited from a plant based diet.

D’Adamo’s theory that blood should determine what you should eat or not eat was therefore debunked and shown to be untrue. Following the blood-type diet will not alter your risks for cardiometabolic diseases, a plant based diet will, and it is recommended for all blood types.

With so many new diets and recommended weight loss practices on social platforms, it’s easy to get lost. Make sure to contact me if you need guidance identifying fad diets from proven scientific diets.

Rebecca Micallef Dalli
Rebecca Micallef Dalli Member of the British Dietetic Association (SENR Registered), MSc. in Exercise and Nutrition Science. SENR Graduate Registrant
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