Dr. Peter D'Adamo developed the blood type diet based on his research that blood type is a key factor in determining a person's nutritional needs. The blood type diet recommends different food guidelines for type A, B, O and AB based on evolutionary theories of blood groups. The type A diet focuses on vegetables and limits meat and dairy. The type B diet emphasizes balance and avoids tomatoes, chicken and pork. The type O diet focuses on lean meats, fruits and vegetables while avoiding wheat and dairy. The type AB diet includes tofu, seafood and green vegetables while avoiding mixing starches and proteins.