According to the New York Times best-selling book Eat Right For Your Blood Type, people of different blood types have specific dietary needs. According to A antigens should opt for vegetarianism while Bs should consume legumes instead of grains, while those with both meat and vegetable antigens can mix. Meanwhile O antigens need to increase protein consumption while decreasing dairy products and wheat consumption.

Dieting for your blood type involves taking into account certain proteins known as lectins found on certain foods. Lectins attach themselves to blood and digestive tissue proteins and prevent absorption of beneficial foods; for Type Os, grains contain lectins which trigger their immune systems into overdrive and cause unwanted inflammation and autoimmunity.

People with type O blood have an impressively robust digestive system that easily handles animal protein, however beans and whole grains containing lectins do not agree. Furthermore, without hydrochloric acid in their stomachs dairy or grain proteins will quickly turn to toxic bacteria, which backs up into muscles and tissues to cause digestive distress. Instead, those who prefer vegetable proteins may benefit from eating vegetable-based proteins from vegetables, fruit as well as quinoa, soy milk, Spirulina or seaweed sources instead.

Coffee can irritate the stomach, so it is essential for Os to select low acid coffee brands such as LifeBoost which uses organic Colombian arabica beans that are free from synthetic pesticides and fertilizers, plus their Go Bag filter to reduce acid. Furthermore, they suggest darker roasts since these have less caffeine than lighter roasts.