In 1901, Karl Landsteiner, an Austrian scientist, discovered that there are four types of blood. These four blood types are named 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 type AB is the least common. If people with type A blood are given type B blood, or people with type B blood are given type A blood, they will probably die.
In 1927, a Japanese doctor, Furukawa Takeji, did a research and found that people with different blood types also have different personalities (性格). He said that people with type A blood are usually calm and serious； people with type B blood are curious (好奇的), cheerful, and outgoing; people with type O blood are generous (慷慨的) and honest; while those with type AB blood are often caring, creative and careful.
More recently, a doctor in the United States wrote a book that connects blood types with what people eat. For example, his book suggests people with type O blood should eat more meat and less bread and people with type A blood should eat more vegetables. His book, Eat Right for Your Type, has been popular with people who want to lose weight. However, Dr. Peter D'Adamo believes that if a person wants to lose weight easily, he had better eat food that matches his blood type. He thinks it will make the person healthier in other ways, too.
