The O blood type diet is an eating plan tailored for individuals with type O positive or negative blood. Naturopath Peter D’Adamo popularized the concept that aligning one's diet with their blood type could enhance overall health and lower the risk of certain diseases. While adherents may report health improvements, these benefits might stem from adopting a generally healthier diet rather than being specifically linked to their blood type. Despite its popularity, the scientific evidence supporting the blood type diet's effectiveness remains scarce.
Understanding the Blood Type Diet
The blood type diet suggests that individuals with different blood types should consume specific foods and avoid others. This approach is based on the premise that blood type influences how the body reacts to lectins, proteins found in foods. According to this theory, lectins can affect the blood and digestive tract, potentially leading to hormonal disruptions.
D’Adamo proposed that people with different blood types react differently to particular types of food and their lectins. As a result, he recommends specific diets for people with these different blood types.
Blood Types and Their Significance
Blood consists of vital components, including plasma, red and white blood cells, and platelets. It also contains antigens, substances on the surface of the cell that trigger the immune system to attack foreign compounds and organisms, such as bacteria. Antigens can also trigger the immune system to attack blood types that have different antigens.
Doctors classify blood types as A, B, AB, and O, further categorizing them as either rhesus (Rh) positive or Rh negative to denote the presence or absence of an antigen called Rh factor.
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For example, a person with O+ blood does not have A or B antigens on the surface of the cells but does have Rh factor. In contrast, O- blood has no A or B antigens and no Rh factor. For this reason, medical experts consider type O- blood to be a universal red cell donor type.
Different blood types may make people more or less susceptible to certain conditions. A large genetic study from 2019, for example, found that people with type A and AB blood have an increased risk of gastric cancer. A 2019 study in Croatia also found an association between the AB blood type and the risk of psychiatric disorders. The researchers suggested that those in the AB blood group are three times as likely as those in other blood groups to have a psychiatric disorder.
The O Blood Type Diet: What to Eat
Proponents of the blood type diet suggest that people with blood type O should consume and avoid certain foods. The diet plan dictates that people in the O blood group should consume “beneficial” animal products, including beef, lamb, mutton, veal, venison, cod, herring, and mackerel. While people looking to follow the blood type O diet should generally avoid dairy and eggs, they can occasionally consume butter, cheeses, such as farmer, feta, mozzarella, and goat’s cheeses, and soy milk. Nuts are a great source of protein and healthful fats, and people following the diet can typically have most nuts, except for the ones in the “foods to avoid” list below. Suitable nuts and seeds, including walnuts, hazelnuts, and almonds, are available to purchase online. Pumpkin seeds and walnuts supposedly provide the most benefits.
People with type O blood tolerate beans. Proponents of the diet believe that the most beneficial beans for these individuals are adzuki beans, pinto beans, and black eyed peas. While most people on the O positive and negative diet should avoid grains, a few can remain in the diet, including amaranth, buckwheat, rice, kamut, and kasha, millet. Some people may also be able to eat gluten-containing grains, while others will be unable to tolerate them. These grains include barley, rye, spelt, oat, Essene bread and Ezekiel bread.
With a few exceptions - which are on the list of foods to avoid - people with type O blood can eat most vegetables, including tomatoes, artichoke, chicory, dandelion, garlic, horseradish, kale, okra, onions, parsley, parsnips, red peppers, sweet potatoes, pumpkin, seaweed, and turnips. Some of the recommended fruits for people with type O blood include plums, prunes, figs, grapefruit, and most berries.
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Spices that people following the diet can enjoy include kelp-based seasoning, iodized salt, parsley, curry, cayenne pepper, chocolate, cocoa, and honey. People following an O positive and negative diet can drink seltzer water, club soda, sparkling water, tea, and wine.
The O Blood Type Diet: Foods to Avoid
Supporters of the diet suggest that people with type O blood may experience unwanted weight gain when they eat particular food groups, such as dairy. Specific products, such as wheat-based foods that contain gluten, may also lead to an inflammatory and autoimmune response.
The diet plan for people with type O blood excludes pork, including ham and bacon, goose, barracuda, pickled herring, catfish, smoked salmon, caviar, octopus, and conch. People following the diet should avoid dairy products not in the “foods to eat” list, including yogurt.
Particular nuts also do not feature in the diet plan, including Brazil nuts, cashews, peanuts, pistachios, and poppy seeds. Beans that proponents of the diet advise against include copper beans, kidney beans, tamarind beans, and lentils, including domestic, green, and red lentils.
The diet also excludes the following grains: corn, gluten, graham, bulgur, durum, sprouted, white and whole wheat, wheat germ and bran, farina, and seven grain. Although people in blood group O tolerate many vegetables well, the advice is that they should avoid vegetables belonging to 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, and cornleek.
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People following the O positive and negative diet should also avoid several specific fruits: melons, including cantaloupe and honeydew, oranges, tangerines, strawberries and blackberries, rhubarb, avocado, and coconut and products that contain coconut. Spices and condiments to avoid in the diet include pepper, both white and black, vinegar, capers, cornstarch and corn syrup, nutmeg, vanilla, ketchup, pickles, mayonnaise, and relish. People with type O blood should avoid drinking the following, according to the diet plan: beer, coffee, distilled liquor, and black tea.
Scientific Evaluation and Criticisms
Research on the blood type diet is limited, and studies have not consistently proven its effectiveness. For example, the authors of a 2014 study concluded that their findings did not support the claims that a blood type diet provides specific benefits. A 2013 review of data relating to the blood type diet also found that no evidence is currently available to verify the benefits of this eating plan.
A 2014 study showed that adhering to the blood type O diet reduced levels of triglycerides in the blood, the storage form of fat. Despite this, the study authors concluded that the drop in triglyceride levels occurred due to factors unrelated to a person’s blood group.
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.
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.
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.
Potential Benefits and Risks
People following a specific blood type diet may report improved health, but this could occur due to them eating more healthful food in general. It is always important for a person to pay attention to how their body reacts to the foods and beverages that they consume so that they can get to know what diet works best for them.
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.
Considerations and Alternatives
When developing a diet, other important factors to consider are beyond blood type. “Ultimately, it’s important to emphasize that choosing a healthy way of eating that best fits your life and that you can stick with for the long-term is the right approach,” says Dr.
There is no one-size-fits-all approach when it comes to diets. Everybody is different and needs individual care and attention. That’s why so many people have found success through our nutritional coaching program.
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.