A diet called The Blood Type Diet has been popular for almost two decades now.

Proponents of this diet suggest that your blood type determines which foods are best for your health.

There are many people who swear by this diet, and claim that it has saved their lives.

But what are the details of the blood type diet, and is it based on any solid evidence?

Let’s have a look.

What is The Blood Type Diet?

The blood type diet, also known as the blood group diet, was popularized by a naturopathic physician called Dr. Peter D’Adamo in the year 1996.

His book, Eat Right 4 Your Type, was incredibly successful. It was a New York Times bestseller, sold millions of copies, and is still wildly popular today.

In this book, he claims that the optimal diet for any one individual depends on the person’s ABO blood type.

He claims that each blood type represents genetic traits of our ancestors, including which diet they evolved to thrive on.

This is how each blood type is supposed to eat:

  • Type A: Called the agrarian, or cultivator. People who are type A should eat a diet rich in plants, and completely free of “toxic” red meat. This closely resembles a vegetarian diet.
  • Type B: Called the nomad. These people can eat plants and most meats (except chicken and pork), and can also eat some dairy. However, they should avoid wheat, corn, lentils, tomatoes and a few other foods.
  • Type AB: Called the enigma. Described as a mix between types A and B. Foods to eat include seafood, tofu, dairy, beans and grains. They should avoid kidney beans, corn, beef and chicken.
  • Type O: Called the hunter. This is a high-protein diet based largely on meat, fish, poultry, certain fruits and vegetables, but limited in grains, legumes and dairy. It closely resembles the paleo diet.

For the record, I think any of these dietary patterns would be an improvement for most people, no matter what their blood type is.

All 4 diets (or “ways of eating”) are mostly based on real, healthy foods, and a huge step up from the standard Western diet of processed junk food.

So, even if you go on one of these diets and your health improves, it doesn’t necessarily mean that it had anything to do with your blood type.

Maybe the reason for the health benefits is simply that you’re eating healthier food than before.

Bottom Line:

The type A diet resembles a vegetarian diet, but type O is a high-protein diet that resembles the paleo diet. The other two are somewhere in between.

Lectins are a Proposed Link Between Diet and Blood Type

One of the central theories of the blood type diet has to do with proteins called lectins.

Lectins are a diverse family of proteins that can bind sugar molecules.

These substances are considered to be antinutrients, and may have negative effects on the lining of the gut (1).

According to the blood type diet theory, there are many lectins in the diet that specifically target different ABO blood types.

It is claimed that eating the wrong types of lectins could lead to agglutination (clumping together) of red blood cells.

There is actually evidence that a small percentage of lectins in raw, uncooked legumes, can have agglutinating activity specific to a certain blood type.

For example, raw lima beans may interact only with the red blood cells in people with blood type A (2).

Overall, however, it appears that the majority of agglutinating lectins react with all ABO blood types (3).

In other words, lectins in the diet are NOT blood-type specific, with the exception of a few varieties of raw legumes.

This may not even have any real-world relevance, because most legumes are soaked and/or cooked before consumption, which destroys the harmful lectins (4, 5).

Bottom Line:

Some foods contain lectins that may cause red blood cells to clump together. Most lectins are not blood type specific.

Is There Any Scientific Evidence Behind The Blood Type Diet?

Research on ABO blood types has advanced rapidly in the past few years and decades.

There is now strong evidence that people with certain blood types can have a higher or lower risk of some diseases (6).

For example, type Os have a lower risk of heart disease, but a higher risk of stomach ulcers (7, 8).

However, there are no studies showing this to have anything to do with diet.

In a large observational study of 1,455 young adults, eating a type A diet (lots of fruits and vegetables) was associated with better health markers. But this effect was seen in everyone following the type A diet, not just individuals with type A blood (9).

In a major 2013 review study where researchers examined the data from over a thousand studies, they did not find a single well-designed study looking at the health effects of the blood type diet (10).

They concluded: “No evidence currently exists to validate the purported health benefits of blood type diets.”

Of the 4 studies identified that somewhat related to ABO blood type diets, they were all poorly designed (11, 12, 13).

One of the studies that found a relationship between blood types and food allergies actually contradicted the blood type diet’s recommendations (13).

Bottom Line:

Not a single well designed study has been conducted to either confirm or refute the benefits of the blood type diet.

Take Home Message

I do not doubt that many people have experienced positive results by following the diet. However, this does NOT mean that this was in any way related to their blood type.

Different diets work for different people. Some people do well with a lot of plants and little meat (like the type A diet), while others thrive eating plenty of high-protein animal foods (like the type O diet).

If you got great results on the blood type diet, then perhaps you simply found a diet that happens to be appropriate for your metabolism. It may not have had anything to do with your blood type.

Also, this diet removes the majority of unhealthy processed foods from people’s diets.

Perhaps that is the single biggest reason that it works, without any regard to the different blood types.

That being said, if you went on the blood type diet and it works for you, then by all means keep doing it and don’t let this article dishearten you.

If your current diet ain’t broken, don’t fix it.

From a scientific standpoint, however, the amount of evidence supporting the blood type diet is particularly underwhelming.