The Blood Type Diet Is Popular Again. Here’s What the Science Says.

PEOPLE OFTEN ADOPT different diets for different reasons. They may start eating Mediterranean-style to improve their heart health, or go vegan for ethical reasons. But what about eating according to your blood type?

This idea was first introduced in a 1996 book, Eat Right 4 Your Type, by naturopathic physician Peter D’Adamo, which suggested that people could improve their health, live longer, and maintain their ideal weight by eating specific food groups based on their blood type, according to Harvard Medical School.

More recently, TikTokers have been talking about the blood type diet and its purported benefits and downsides. But is there any scientific evidence that the diet works? Here’s what experts say.

What Is the Blood Type Diet?

• People with type O blood should consume high-protein foods, including meat, fish, fruits, and vegetables, but limit legumes and whole grains.
• People with type A should eat a vegetarian diet, with lots of fruits, vegetables, and whole grains, and avoid meat.
• People with type B or AB blood should eat a balanced diet covering all food groups.

The theory is that there’s a link between blood type and how well you digest different foods, and that eating based on blood type could improve digestion, help maintain a healthy weight, boost energy, and lower your risk of disease.

For example, the book links type O is to the earliest humans, who were hunter-gatherers and ate mostly animal proteins. Type A possibly evolved after humans began farming and ate more fruits and vegetables, while B types may have arisen from nomadic tribes who ate dairy. AB eating recommendations are between the suggestions for types A and B.

Does It Work?

THERE’S NOT ENOUGH scientific evidence to suggest that it does, as no high-quality studies have been done to verify claims about the blood type diet, explains Randy Gould, D.O., a cardiologist at Manhattan Cardiology and a contributor to LabFinder.

A 2013 systematic review found no studies showing benefits of a blood type diet. However, a 2014 study suggested that people who followed a blood type diet had lower BMI, waist circumference, blood pressure, cholesterol, and blood sugar—but the improvements weren’t actually linked to subjects’ blood types.

Blood type also wasn’t linked to improvements in body weight, body fat, blood lipids, or glycemic control for people who followed a low-fat vegan diet, according to research published in 2021.

Any potential benefits of the diet are likely to do with what it encourages people to eat and not eat, rather than their actual blood type.

“All three types of diets for different blood types encourage many fruits and vegetables and also avoidance of ultra-processed foods,” Weinandy says. “This is healthy for anyone.”

It’s also important to note that blood type may play a role in other aspects of health, Dr. Gould says. Some studies have shown that people with type O blood have a lower risk for heart disease compared to people with types A, B, and AB.

And, people with type A or AB may be at a higher risk for gastric cancer, and types A, B, and AB at a higher risk for pancreatic cancer, according to Northwestern Medicine.

Who Should (and Shouldn’t) Try the Diet?

ONE BARRIER TO trying the diet is that most people actually don’t know their blood type, according to the American Red Cross. To find out, you can ask your doctor to test it, or if you donate blood, they can likely tell you.

Trying the blood type diet could be beneficial for people who don’t normally eat many fruits, vegetables, or whole grains, Dr. Gould says.

However, it’s “very prescriptive and lacking in evidence,” Weinandy says. “Cutting out entire food groups like dairy or even wheat when it likely isn’t necessary can cause inadequate nutrient intake.”

She doesn’t recommend the blood type diet to anyone: “Like most unproven diets and claims, there may be some truth or good points to it—in this case, eating a lot of whole plant foods—but it’s surrounded by negatives like cutting out food groups.”

Instead, Weinandy suggests following the Mediterranean diet, which she says is less restrictive, includes a wide range of food groups, and has lots of research to show it improves health.