The Blood Type Diet urges people to eat certain foods and avoid others based on their blood type. Peter J. D'Adamo, the author of "Eat Right for Your Type: The Individualized Diet Solution to Staying Healthy, Living Longer & Achieving Your Ideal Weight," maintains that blood types affect the digestive system and that your food should be determined by whether you have type O, A, B or AB blood.

 

For example, since blood type O is humanity's oldest bloodline, D'Adamo contends that the digestive tract retains the memory of ancient times and thus these metabolisms will benefit from lean meats, poultry and fish, with restricted grains, breads, and legumes, and that O-types will benefit from vigorous exercise. Likewise, the "modern" blood type AB set is said by D’Adamo to have a sensitive digestive tract and should steer clear of chicken, beef and pork and instead indulge on seafood, tofu, dairy and most produce — as well as engaging in calming exercises.

 

The consensus among many experts is that the theory is unsupported by scientific evidence; that said, the diet may suit people looking for a plan that doesn't require the tracking of calories or fat grams.