Generally, a person's blood type does not affect the food he should eat, so those with blood type O should consume a balanced diet with an emphasis on fruits, vegetables and lean protein, according to WebMD. Those with specific conditions, such as diabetes, should follow diets according to their needs.
The concept behind the Blood Type Diet is that people should eat foods that support their specific blood type in order to optimize health, according to WebMD. Eating the right foods according to blood type helps support digestion, energy levels, disease prevention and weight loss. Exercise plays an important part in the diet plan. Those with type O blood should engage in regular aerobic exercise, such as running and cycling for up to an hour per day at a vigorous intensity.
Peter D'Adamo, creator of the Blood Type Diet, describes the concept in his book, "Eat Right 4 Your Type," reports the San Francisco Chronicle. People with type O blood inherited blood cell antibodies from their ancient ancestors. In order to ensure the proper chemical relationship between blood cells and lectins from food, people with this blood type need to eat what their prehistoric ancestors would have been eating.
As of 2015, the effectiveness of this diet is not supported by scientific evidence, states the San Francisco Chronicle. Those considering making changes to their eating lifestyle should consult a doctor.