The Blood Type Diet Myth That Science Has Disproved

The Blood Type Diet is one fad that has managed to stick around for years. First introduced in 1996, it argues that people should eat according to their blood type. But recent research suggests that when people see benefits from the diet, those results are not tied to blood type itself.

The diet was popularized by Peter D'Adamo in his book Eat Right 4 Your Type. He claimed that the ABO blood group system creates a genetic tendency toward certain foods, so what works best for one person may not work for another. In his view, Type A people are better suited to a mostly vegetarian diet, Type B people should emphasize dairy, Type O people do best with a high-animal-protein plan, and Type AB is a blend of A and B. For those unsure of their blood type, he suggested looking at parental blood types as a guide.

D'Adamo also argued that chronic inflammation in the modern world comes from a one-size-fits-all approach to eating, and that more personalized diets are more effective. His theory also centers on lectins, sticky proteins found in many foods. The book claims that some blood types react poorly to certain lectins, so avoiding those foods can help reduce inflammation.

What science says about the Blood Type Diet

Many people say the Blood Type Diet works for them, and the book has received thousands of four- and five-star reviews. Still, the scientific evidence is weak. A systematic review published in the American Journal of Clinical Nutrition in 2013 found no support for the idea. The next year, a PLoS One study tracked people on the four diet versions and measured markers such as body mass index, triglycerides, and waist circumference. Improvements were seen in people following the A, AB, and O plans, but those gains appeared across blood types, not just among people whose blood type matched the diet. The Type B diet did not produce similar improvements.

Two later studies also failed to provide convincing evidence. In a 2018 study of nearly 1,000 overweight adults, BMI and waist circumference improved across the diets, but people with matching blood types did not benefit more than anyone else. In 2021, researchers examining participants in a larger weight-loss study found no connection between blood type and outcomes on a low-fat vegan diet.

Why the Blood Type Diet can still seem effective

If the evidence does not back up the Blood Type Diet, why have so many people praised it for decades? One likely reason is that, for many followers, it simply leads to better eating habits. On the Type A plan, for example, many people swap processed foods for fruits, vegetables, and eggs, which can improve how they feel regardless of blood type. Those on the Type O plan may notice more energy and greater fullness after shifting toward lean animal protein and fiber-rich vegetables.

Even the Type B plan, which showed fewer measurable benefits in studies, still promotes nutrient-dense nuts, vegetables, seafood, and dairy. For people coming from a heavily processed diet, those changes alone can lead to noticeable improvements in health and well-being.

In the end, the Blood Type Diet mainly removes many of the processed fats and sugars that are common in unhealthy modern diets. That shift may be enough for some people to see positive results, but it is unlikely that blood type is the reason. A nutritious, balanced diet remains the best approach for long-term health.