The Blood Type Diet, created by Dr. Peter J. D’Adamo—author of Eat Right for Your Type—is based on the idea that your blood group determines how your body reacts to different foods. According to D’Adamo, eating in alignment with your blood type helps improve digestion, increase energy, support weight loss, and enhance overall health.

Because blood type O is the most common, here’s a breakdown of what the diet recommends for people with O positive and O negative blood.

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What Defines Blood Type O?

Blood type is based on the presence of antigens and antibodies:

• Antibodies help your immune system identify and destroy foreign substances.

• Antigens sit on the surface of red blood cells.

Blood group O has no antigens, but has both anti-A and anti-B antibodies. That’s why type O blood can be donated to any of the major blood groups.

Type O can be:

• O positive (with the RhD antigen)

• O negative (without the RhD antigen)

O positive is the most common.

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What Is the Blood Type O Diet?

According to D’Adamo, people with blood type O naturally produce more stomach acid, allowing them to digest protein and fat efficiently. Therefore, the diet emphasizes lean meats, fish, and certain vegetables, while limiting grains, dairy, and legumes.

A major theme of this diet is lectins—plant proteins that D’Adamo says can cause inflammation or immune reactions when eaten by the “wrong” blood type.

Although the concept is debated, many followers report improved digestion and energy when adopting this diet.

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Foods to Eat on a Type O Diet

1. Protein (Highly Recommended)

Type O individuals thrive on high-protein foods:

Best meats & poultry

• Beef

• Lamb

• Veal

• Venison

• Most poultry

Best fish & seafood

• Cod

• Herring

• Trout

• Mackerel

• Tuna

These are rich in iodine, which supports thyroid health—a common concern for type O individuals.

🚫 Meats to avoid

• Pork and all pork products

• Bacon

• Octopus

• Salmon roe (caviar)

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2. Beans & Legumes

Certain beans support type O metabolism, while others may disrupt thyroid function.

Best options

• Black beans

• Adzuki beans

• Green/string beans

🚫 Avoid completely

• Lentils

• Soybeans

• Green peas

• Peanuts and peanut butter

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3. Fruits

Some fruits help balance the naturally high stomach acid of type O individuals.

Best options

• Plums

• Prunes

• Figs

• Occasional cranberries, raspberries, gooseberries

🚫 Avoid

• Oranges

• Melons

• Blackberries

• Strawberries

• Kiwifruit

These may interfere with metabolism or increase digestive stress.

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4. Vegetables

Leafy greens are especially beneficial.

Best options

• Kale

• Lettuce

• Broccoli

• Red peppers

• Okra

• Ginger root

🚫 Avoid completely

• Cabbage

• Cauliflower

• Brussels sprouts

• Mushrooms

• Pickled vegetables

These may interfere with thyroid hormone production or irritate digestion.

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5. Dairy Products

Type O individuals generally do not digest dairy well.

🚫 Avoid

• Milk

• Yogurt

• Most cheeses

• Butter (limit)

• Eggs (limit)

✔️ Occasionally acceptable

• Small amounts of mozzarella or butter

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6. Grains

According to this diet, type O individuals should minimize grains—especially wheat—because gluten can disrupt insulin metabolism.

Avoid

• Wheat bread

• Most grains

Accepted alternatives

• Rice

• Quinoa

• Millet

• Amaranth

• Spelt

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Other Lifestyle Notes for Type O

• Most caffeinated drinks and alcohol should be limited.

• Water, herbal tea, and occasional wine are acceptable.

• The diet claims to help improve dopamine balance, supporting mood and reducing stress.

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Is the Blood Type O Diet Supported by Science?

The diet is controversial. Critics argue:

• There is little scientific evidence connecting blood type and ideal diet.

• Improved health may simply come from eating more whole foods and avoiding processed foods.

D’Adamo disputes these critiques, citing research on lectins and metabolic differences between blood types.

Whether or not the science convinces you, many people report positive changes when following the plan.