A diet based on the theory that people with different blood types should eat different types of foods. Popularized by Peter D'Adamo in the book Eat Right For Your Type (1996), this diet has developed a large and loyal following. The basic idea behind the theory is that at different stages of evolutionary history, humankind's dietary requirements changed based on environmental factors.

Blood Type O first developed during the hunter-gatherer stage, circa 50,000 - 40,000 B.C. The Cro-Magnon hunters thrived on meat, but also ate small amounts of berries, grubs, nuts, roots, and small animals. As the population migrated out of Africa and encountered changing environmental conditions, people began to develop varied racial characteristics.

Sometime between 25,000 and 15,000 B.C., Type A blood first appeared, somewhere in Asia or the Middle East. This was spurred by agriculture and animal domestication. For the first time, humans began to settle down in stable communities, leading to a significant change in diet and lifestyle. The Type A blood mutation allowed people in farming communities to better digest cultivated grains.

Blood type B developed between 15,000 and 10,000 B.C. near what is today known as Pakistan and India. It was spread more widely by Mongolian tribes that swept throughout eastern Asia. Their culture was based upon herding and domesticating animals.

Blood type AB is the most modern (and rare), having developed only about 1,000 years ago. This blood type came about as a result of intermingling of Eastern invaders and Europeans after the fall of the Roman Empire. As the name suggests, ABs are a combination of types A and B.

According to D'Adamo's theory and long time practice of many thousands of people, these evolutionary differences lead to practical dietary considerations. Type Os are advised to exercise heavily and eat lots of meats, particularly red meats. They should avoid all types of grains, particularly wheat and corn. Type Os should severely restrict their use of dairy products. Most types of vegetables and fruits are fine.

Type As are pretty much the opposite of Os. They are encouraged to be mostly vegetarian, although fish and chicken are fine. Soy foods and pineapple are particularly beneficial to Type As.

Type Bs can eat a more balanced diet than Os or As. Dairy products, meats, and grains are all acceptable. Some foods are still problematic, though, including corn, lentils, peanuts, sesame seeds, buckwheat, wheat, and chicken.

It is somewhat more difficult to summarize the ideal AB diet, as it is somewhat of a strange combination of the A and B diet. ABs don't do well on red meat, however, and kidney beans, lima beans, seeds, corn, buckwheat, and wheat should be avoided as well. Soy, seafood, dairy, green vegetables, kelp, and pineapple are all highly beneficial for ABs.

Negative and positive Rh factors have no bearing on this diet.