The blood type diet is diet that was promoted in the book Eat Right 4 Your Type by Dr. Peter D’Adamo. In the book it was claimed that the most important factor in determining a healthy diet is the person’s ABO blood type [1]. The diet became very popular in the late 90’s and the beginning of the new millennia. The diet claims that you should follow a diet according to your blood type. Even almost 20 years later, the book has 4.5 stars on Amazon and it continues to sell.

What exactly is the blood type diet?

Dr. D’Adamo lays out 4 different diets, one for each of the blood types there are 4 blood types, and therefore 4 diets recommended in the book.

Type A: The agrarian or cultivator. Blood type A people who should eat plant rich diets with no red meat. Type A diets should most resemble a vegetarian. Type B: The nomad. People with blood type B should eat plants, and can eat meat (except chicken and pork), and some dairy. They should avoid wheat, corn, lentil, tomatoes, and a few other foods. Type AB: The enigma. This person is a ‘mix’ between types A and B, and should eat a diet rich in seafood, tofu, dairy, beans and grains. However, they should exclude kidney beans, corn, beef and chicken. Type O: The hunter. People with blood type O should eat high protein diets that are rich in meat, fish, poultry, some fruits and vegetables, but limit grains, legumes and dairy (sound familiar Paleo people?).

These diets look generally healthy. What, then, is the problem? The problem is that there are hundreds of conflicting diet recommendations, and this is just one of them.

So what does science have to say about this one?

A robust systematic review found no evidence to support the blood type diet, even though in the book, Dr. D’Adamo says the diet is justified by scientific arguments derived from biology, physiology, immunology, and epidemiology. However, the author launches them simply as facts – not proving them with any scientific evidence. He is playing off people’s ignorance of biology.

The review in the American Journal of Clinical Nutrition (2013) identified 1,415 articles that may be able to shed some light on the blood type diet, and they concluded the following:

There is currently no evidence that an adherence to blood type diets will provide health benefits, despite the substantial presence and perseverance of blood type diets within the health industry.

The Norwegian Society for Nutrition held a one day seminar in February 2001 to try and identify any truths in the diet. They found that “the book is strongly marked by imagination.”

As anyone would, Dr. D’Adamo responded to these claims, saying that there has been little popular interest and money to study the link between blood types and diet. However – he’s sold over 7 million copies of his book, and this is plenty of money to fund a study. And that’s exactly what he did. In 1996 he wrote that he was beginning the 8th year of 10 year study on the blood type diet’s affect on reproductive cancers. He wrote

By the time I release the results in another two years, I expect to make it scientifically demonstrable that the blood type diet plays a role in cancer remission.

The results? 20 years later, they are still not released.

Dr. D’Adamo uses big words, but his description of blood type evolution is fundamentally wrong, making it difficult to believe any other scientific claims in the book. First, he claims that blood type O is the “original” blood type. However, other evidence shows that A was the first blood type to exist, and many agree that more studies are needed to grasp the evolution. Dr. D’Adamo also claims that blood type AB is approximately 1,000 years old – appearing somewhere between 500 BC and 900 AD. This claim is somewhat absurd – while he is correct that it is the youngest blood type, it first appeared about 260,000 years ago.

If it’s so wrong why does the book get sold and why do people see results?

Fad diets work because there is so much conflicting nutritional advice out there. And people want quick solutions to their very real health and diet problems. Read more about that here. And why to people see results? Look back at the diets for each blood type. While they may not be right for you, none of them extremely unhealthy. Results that people may see from following the blood type diet may be because that individual may simply just be eating healthier than before.

Whether you choose to follow on the 4 diets set out by Dr. D’Adamo, know that if you’re seeing results, it’s because you’re eating better – not because of your blood type.

To learn more, watch this video below from NutritionFacts.org:

Acknowledgement

Video courtesy of Dr. Michael Greger and NutritionFacts.org.

References

[1] D’Adamo, Peter J. “Eat Right 4 Your Type.” Clinical Nutrition Insight 25, no. 6 (1999): 5.