In 1901, an Austrian scientist found out that there are four types of blood (血型) . He named them A, B, AB, and O. People have one of these four types. Blood type O is the most common around the world. Blood type A is the second most common, and blood type AB is the least common.

In 1927, a Japanese doctor found that people with different blood types have different personalities, too. He said that people with type A blood are usually calm and serious; people with type B blood are cheerful and outgoing; people with type O blood are generous(慷慨的) and honest; while those with type AB blood are often caring and creative.

Later on, a doctor in the United States wrote a book. That connects(联系) blood types with what people eat. The book suggests people with type O blood should eat more meat and less bread. A diet for people with type A blood has more vegetables. His book, Eat Right for Your Type, has been a hit with people who want to lose weight. However, Dr. Peter D’Adamo believes that eating food that matches a person’s blood type will make the person healthier.