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The blood type diet recommends that people with different blood types eat differently. For example, people with type O blood may want to eat more protein. Although the diet has become popular, it isn’t based on scientific evidence.

The blood type diet was made popular by Dr. Peter D’Adamo, a naturopathic physician and author of the book “Eat Right 4 Your Type.”

In his book and website, he claims that following a specific diet and exercise regimen based on your blood type can optimize your health and reduce your chance of developing particular health conditions.

This might be because the diet promotes healthy eating and exercise, which provides health benefits for people, regardless of their blood type.

D’Adamo also claims that blood types represent the genetic traits of our ancestors, and his diet plans are based on what foods our ancestors thrived on.

For example, he claims that blood type O is the oldest blood type, associated with ancestors who were hunter-gatherers. He says people with blood type O tend to have strength, be lean, and have a productive mind.

This is scientifically unproven. One study even states that the A blood type is the oldest.

In addition, D’Adamo associates certain health conditions with type O blood, such as digestive issues, insulin resistance, and a poor-performing thyroid. These associations with blood type are also not scientifically proven.

D’Adamo’s blood type diet recommends consuming certain foods based on the four blood types.

Your blood type is determined by your genetics. There are four different types of blood:

  • O
  • A
  • B
  • AB

There’s also another categorization for blood that the blood type diet doesn’t account for. Your blood may or may not have a protein known as Rh. This results in there being eight different types of blood.

Type O-positive blood is the most common type, meaning you have O blood with an Rh factor. Note that D’Adamo’s blood type diet only includes a type O diet, not a type O-positive diet.

According to D’Adamo, those with type O blood should focus on eating lots of protein, like one would in a paleo or low-carbohydrate diet.

He recommends that you consume:

  • meat (particularly lean meat and seafood for weight loss)
  • fish
  • vegetables (noting that broccoli, spinach, and kelp are good for weight loss)
  • fruits
  • olive oil

The O blood type diet should also be paired with vigorous aerobic exercise, says D’Adamo.

His diet plan also recommends taking supplements. These supplements are supposed to target the health conditions associated with type O blood, like digestive issues.

The paleo-oriented or low-carbohydrate diet that D’Adamo recommends for those with type O blood focuses on avoiding:

  • wheat
  • corn
  • legumes
  • kidney beans
  • dairy
  • caffeine and alcohol

There’s no scientific evidence that supports the blood type diet. Many studies have debunked the diet while other studies have found some benefits of the diet unrelated to blood type.

One 2014 study states that the diet may be popular because it emphasizes eating whole foods, avoiding processed foods, and exercising.

These principles are associated with many diets and are recommendations commonly given by doctors and nutritionists to improve or maintain health.

In 2013, a systematic review in the American Journal of Clinical Nutrition looked at 16 previous studies on blood type diets. The review concluded that there’s no current evidence that supports blood type diets.

Furthermore, the theories behind the diet need to be studied by having two different groups of participants in a study, one that participates in the diet and one that doesn’t, all with the same blood type. This will determine the effectiveness of the blood type diet.

Another study in PLOS One maintained that the O blood type diet lowered serum triglycerides, consistent with other low-carbohydrate diets. The study didn’t find a link between the recommended diet and blood type, however.

Despite the lack of evidence that blood type can determine a healthy diet for you, there are many studies on how your blood type can determine particular health conditions.

Some studies have linked blood types with certain health risks:

  • One 2012 study linked a lower risk of coronary artery disease to having an O blood type.
  • Another 2012 study showed that blood type can be linked to your reaction to certain bacteria and conditions like pancreatic cancer, deep vein thrombosis, and heart attack.

There’s still more to understand about blood type and associated health conditions that may be discovered in future scientific studies.

Despite the lack of scientific evidence of the blood type diet, it remains a topic of discussion in the diet culture.

The four diets in the blood type diet emphasize eating healthy whole foods and exercising, which can be beneficial to your health. But the diet could still be risky.

For example, the O blood type diet emphasizes a high intake of animal proteins, which may lead to other health problems.

Your blood type alone doesn’t determine your overall health, and you may put yourself at risk by engaging in the blood type diet without your doctor’s advice.

There’s no evidence that the blood type diet works.

You may think that your O blood type gives your body a certain profile, but this theory and the diet supporting it aren’t validated by researchers and medical professionals.

If you need to lose weight or maintain a healthy weight, see a doctor to determine the best course of action for you as an individual. Don’t rely on popular but unproven diets to guide your eating and exercise habits.