Quick answer
The blood type diet is not supported by evidence. A systematic review found no studies showing health benefits specific to matching diet to blood type, and a cross-sectional study found that where a “type-A” eating pattern was linked to better cardiometabolic markers, the association held regardless of a person's ABO blood type. In other words, any benefit tracked the eating pattern itself, not the blood group.
What the blood type diet claims
The theory was popularised in 1996 by naturopath Peter D'Adamo in Eat Right 4 Your Type. It proposes that each ABO blood group evolved at a different point in human history and therefore digests certain foods better than others. It also claims that dietary proteins called lectins interact differently with each blood type's antigens.
| Blood type | Claimed origin | Recommended eating pattern |
|---|---|---|
| Type O | Hunter-gatherer | High-protein: meat, fish, vegetables; limit grains, beans, dairy |
| Type A | Agrarian | Mostly vegetarian: vegetables, fruit, legumes, whole grains |
| Type B | Nomadic | Balanced omnivore: dairy, meat, vegetables; avoid corn, wheat, lentils |
| Type AB | Modern mix | Blend of A and B: seafood, dairy, tofu, greens; avoid smoked meats |
What the research found
A 2013 systematic review published in the American Journal of Clinical Nutrition searched for studies testing whether health outcomes improved when people ate according to their blood type. Of more than 1,400 records screened, none met the criteria for a valid test of the hypothesis. The authors concluded that no evidence supports the claimed benefits.
A 2014 cross-sectional study in PLOS ONE analysed 1,455 young adults and found that a “type-A” (largely plant-based) eating pattern was associated with lower BMI, blood pressure, cholesterol and other cardiometabolic markers—but those associations held regardless of a person's ABO blood type. Because it measured people at a single point in time, it shows association rather than proof from a controlled or long-term trial, and it does not support matching diets to blood type.
The evolutionary story behind the theory is also questionable. Type O is not clearly the single ancestral human blood type, and ABO blood groups are present in other primates, predating agriculture by a very long time.
Is it harmful?
The individual diets are mostly variations on reasonably healthy eating, so following one is unlikely to be dangerous for a healthy adult. Potential downsides include unnecessary food restriction, cost, and the risk of eliminating food groups such as dairy or whole grains without a nutritional reason. People with existing conditions, pregnant or breastfeeding people, and children should talk to a clinician or registered dietitian before making significant dietary changes.
What blood type does reliably tell you
Blood type is highly informative for transfusion compatibility, Rh factor management in pregnancy, and inheritance. Use our compatibility chart or baby blood type calculator to explore those.