The four different blood types are types A, B, AB and O. The type O blood group is the most common in populations worldwide, according to the National Center For Biotechnology Information. Each blood group is classified according to marker proteins called antigens, which affect the body's immune response. Type O positive blood also contains an antigen called the rhesus factor. According to Dr. Peter D'Adamo, author of "Eat Right 4 Your Type," blood type affects personality and energy levels and can affect the risk of developing certain diseases. For blood type O, Dr. D'Adamo recommends a high-protein, low-carbohydrate diet.
Meat and Fish
According to D'Adamo, the earliest humans were hunter-gatherers whose blood group was Type O and whose diet consisted of wild game and edible plants. D'Adamo explains that Type O diet should mainly consist of first-class protein from sources such as meat and seafood. If your blood group is Type O, you should eat meats such as beef, lamb, mutton, veal and venison, and fish such as cod, herring and mackerel. People with O positive blood have high amounts of stomach acid and can therefore digest meat easily, says D'Adamo. Dr. Michael Lam advises you to avoid bacon, ham, goose, pork, barracuda, pickled herring, catfish, smoked salmon, caviar, octopus and conch if your blood type is O.
Grains and Beans
If your blood type is O, avoid gluten from sources such as bread and pasta because it slows your digestion. Lam suggests that you eat Essene and Ezekiel breads and buckwheat, barley, rice, millet, rye and spelt. You should avoid corn, bulgar wheat, durum wheat, whole wheat, wheat germ, oats and bran. Lam explains that if you are blood type O, some varieties of beans "make muscle tissue slightly less acidic and inhibit the metabolism of other nutrients." He recommends eating aduke, azuki and pinto beans and black eyed peas, and avoiding copper, navy, kidney and tamarind beans and red and green lentils.
Vegetables and Fruit
Lam explains that people with type O blood lack blood clotting factors, namely vitamin K, which is provided by green leafy vegetables such as kale and spinach. Other beneficial vegetables are artichoke, chicory, garlic, horseradish, leeks, onions, parsnips, red peppers, sweet potatoes, pumpkin and turnips. Avoid vegetables from the brassica family, such as cabbage and cauliflower, because they can inhibit thyroid function, and mushrooms, because their high mould content can irritate the digestive tract. Vegetables from the nightshade family, such as potatoes and eggplant, are also best avoided because they may cause arthritic conditions. Choose dark red, dark blue and dark purple fruits, such as plums. Avoid acidic fruits such as oranges, strawberries and rhubarb, and avoid melon due to its high mould content.
Dairy Produce and Oils
If your blood type is O, you should severely restrict your intake of dairy produce, such as cow's milk and yoghurt, and of eggs, says Lam, because these foods can trigger digestive problems. Lam explains that you can eat some butter, feta cheese, mozzarella cheese, goat's cheese and soy milk. Olive oil and flax seed oil are very beneficial. However, you should avoid corn, peanut, cottonseed and safflower oils.