The O positive (and O negative) blood type diet?


By Lori Smith BSN MSN CRNP
Reviewed by Natalie Butler, RD, LD

Knowing your blood type can often be thought of as useful only if you need a blood transfusion. However, there is another argument that says eating for a specific A, B, AB, or O blood type may offer health benefits.

Popularized by naturopath Peter J. D’Adamo, diets based on blood type attempt to achieve good overall health and lower the risk of developing certain diseases.

Despite its popularity, there has yet to be any rigorous scientific study on the blood-type diet, as stated by D’Adamo himself.

However, one exception was a 2014 study published in PLoS One, which concluded: “the findings do not support the blood-type diet hypothesis.”

In addition, the American Journal of Clinical Nutrition carried out a review of data related to the blood type diet and stated: “No evidence currently exists to validate the purported health benefits of the blood type diets.”

Although scientific evidence is lacking, in this article, we learn about why some believe that a person’s blood type may influence their diet, and the proposed benefits of eating for the O blood groups.

Fast facts on the O positive (and O negative) blood type diet:

  • Research has shown that some blood types are a risk for developing certain diseases or conditions.
  • People with type O blood have been shown to have higher levels of stomach acid than those with other blood types, which make digesting proteins and fats easier for this group.
  • O blood is unique in that it has both A and B antibodies in its plasma, although not on the cells themselves, so it will not attack A or B blood types as foreign invaders.
  • Meats and animal products, such as fish and poultry, are at the top of the go-to list for the type O blood diet, as they are metabolized well by this blood group.

What is the O blood type?

Blood type O RH positive being collected.

Blood type O can be positive (O+), or negative (O-).

Blood is comprised of many vital components, including plasma, red and white blood cells, and platelets.

In addition, the blood contains antigens. These substances trigger the body’s immune system to attack foreign invaders, such as bacteria. Antigens can also attack “foreign” blood types that have different antigens.

Blood types are classified as A, B, AB, and O, and are further grouped by the presence or absence of an antigen called Rh factor. This makes them either Rh positive or Rh negative.

For example, O+ blood does not have A or B antibodies on the surface of the cells, but it is positive for the presence of Rh factor. In contrast, O- blood does not have A or B antibodies or Rh factor. For this reason, type O- blood is considered a universal red cell donor type.

Eating for your blood type

Different blood types may make people more or less susceptible to certain conditions. Some research has suggested that certain blood types have been linked to an increased risk of pancreatic cancer, blood clots, and heart attacks.

As an example of this, some research has indicated that those with O type blood are at a lower risk of developing coronary heart disease but at a higher risk of peptic ulcers.

According to D’Adamo, a chemical reaction occurs when the blood comes in contact with certain foods, specifically with a protein called lectin.

Lectins, which are found in food, have a direct effect on the blood and the digestive tract. The protein binds to cells within the body, causing them to clump together and, potentially, to cause hormonal disruptions. This effect on the body is similar to a foreign substance being present.

D’Adamo suggests that people with different blood types react differently to different types of food and their lectins. As a result, he recommends specific diets for people with these different blood types.

Some research has shown that many lectins react with all types of blood, however, not specific ones.

Foods to eat

According to the Blood Type Diet, for the best dietary health based on blood type, certain foodsshould either be eaten or avoided in the type O group.

The following foods are those that supporters of the Blood Type Diet recommend for those with O type blood. It is worth noting again that there is little reliable evidence to support the use of this diet.

Animal proteins

The diet recommends that people with O blood types should consume “beneficial” animal products, including:

  • beef
  • lamb
  • mutton
  • veal
  • venison
  • cod
  • herring
  • mackerel

People with type O blood following the diet are allowed to consume most meat products, including cold-water fish. Exceptions are listed further down this article.


Although dairy and eggs should be avoided, people following the diet can occasionally consume products including:

  • butter
  • cheeses, such as farmer, feta, mozzarella, and goat cheese
  • soy milk


Nuts are a great source of protein and healthy fats, and people following the diet can typically have most nuts, except for the ones listed in the “avoid” list. Suitable nuts and seeds are available to purchase online, including walnutshazelnuts, and almondsPumpkin seeds and walnuts are believed to be the most beneficial to eat.


Most beans are believed to be well-tolerated by people with type O blood, the most beneficial being:

  • aduke beans
  • azuki beans
  • pinto beans
  • black-eyed peas


Different types of grains.

Only a few types of grains, including buckwheat, barley, rice, and millet are acceptable in a type O diet.

While most grains should be avoided, there are a few that are tolerated, including:

  • amaranth
  • barley
  • buckwheat
  • rice
  • kamut
  • kasha
  • millet
  • rye
  • spelt
  • essene and ezekiel breads

Many of the more obscure grains are available to purchase online, including amaranthkamut, and kasha, as well as ezekiel breads.


Except for a few that should be avoided, many vegetables are believed to be well-tolerated. Some of those recommended for the diet include:

  • tomatoes
  • artichoke
  • chicory
  • dandelion
  • garlic
  • horseradish
  • kale
  • okra
  • onions
  • parsley
  • parsnips
  • red peppers
  • sweet potatoes
  • pumpkin
  • seaweed
  • turnips


As with vegetables, most fruits are believed to be well-tolerated. Some of the recommended fruits for people with type O blood include:

  • plums
  • prunes
  • figs
  • grapefruit
  • most berries

Spices and condiments

Spices that people following the diet can enjoy include:

  • kelp-based seasoning
  • iodized salt
  • parsley
  • curry
  • cayenne pepper
  • chocolate
  • cocoa
  • honey

Many of these ingredients may be purchased online, including kelp-based seasoning and iodized salt.


Drinks that people following the diet can enjoy include:

  • seltzer water
  • club soda
  • tea
  • wine

Foods to avoid

Supporters of the diet state that people with type O blood may experience unwanted weight gain when they eat certain food groups, such as dairy and gluten-containing wheat products. These foods may lead to an inflammatory and autoimmune response.

Animal proteins

The diet recommends that people with type O blood should avoid:

  • pork, including ham and bacon
  • goose
  • barracuda
  • pickled herring
  • catfish
  • smoked salmon
  • caviar
  • octopus
  • conch


People following the diet should avoid dairy products, specifically:

  • those not mentioned in the “allowed” list above
  • yogurt


Certain nuts should be avoided according to the diet, including:

  • Brazil nuts
  • cashews
  • peanuts
  • pistachios
  • poppy seeds


Certain beans should be avoided by people following the diet, including:

  • beans, such as copper, kidney, and tamarind beans
  • lentils, such as domestic, green, and red


The diet recommends that people with type O blood avoid:

  • corn
  • gluten
  • graham
  • bulgur, durum, sprouted, white and whole wheat, wheat germ, and bran
  • farina
  • oat
  • seven-grains


Brassica family of vegetables, including broccoli, cauliflower, Brussel sprouts, and cabbage.

The Brassica family of vegetables, including broccoli, cauliflower, Brussel sprouts, and cabbage, is recommended to be avoided on the O diet.

Although many vegetables are well-tolerated, it is recommended that people following the diet avoid:

  • vegetables in the Brassica family, including cabbage, Brussels sprouts, cauliflower and mustard greens
  • alfalfa sprouts
  • shiitake mushrooms
  • fermented olives
  • vegetables from the nightshade family, including eggplant and potatoes
  • corn
  • avocado
  • leek


As with vegetables, the diet recommends avoiding a number of specific fruits:

  • melons, cantaloupe, honeydew
  • oranges
  • tangerines
  • strawberries and blackberries
  • rhubarb
  • coconut and products that contain coconut

Spices and condiments

Spices and condiments to be avoided in the diet include:

  • pepper, both white and black
  • vinegar
  • capers
  • cinnamon
  • cornstarch and corn syrup
  • nutmeg
  • vanilla
  • ketchup
  • pickles
  • mayonnaise
  • relish


Drinks that the diet recommends avoiding include:

  • beer
  • coffee
  • distilled liquor
  • black tea


As stated, there is currently no strong evidence to prove that this diet is effective, or to support its use.

People following a specific blood type diet may report improved health, but this could occur due to eating more healthful food in general, rather than due to anything linked with their blood type.

It is always important for people to pay attention to their bodies and get to know which foods work best for them. Keeping a well-balanced diet, full of nutrient density and variety is best.

As with any diet or exercise program, it is important to speak with a doctor before embarking on a specific diet for blood type.