One of the biggest red flags to me is that despite being around for 40 years now, the Blood Type Diet completely lacks robust scientific evidence for its claims. In fact, a growing body of evidence calls those claims into serious question. One major systematic review evaluated the claim that adherence to blood type diets provides health benefits. It concluded that no evidence currently exists to validate any purported health benefits associated with blood type diets.
Another study specifically tried “…to determine the association between blood type diets and biomarkers of cardiometabolic health and whether an individual’s ABO genotype modifies any associations.” The authors found that following certain blood type diets — but not all — reduced cardiometabolic risk factors. However, these associations were independent of an individual’s blood type, so the findings do not support the blood type diet hypothesis.
A diet based predominantly on whole plant foods, on the other hand, has been shown time and time again to reduce risk for chronic diseases and even reverse conditions like heart disease and type 2 diabetes in a great many people. And this is true regardless of blood type.
For example, a 16-week randomized clinical trial published in 2021 looked at the benefits of a plant-based diet compared to a control (omnivorous) diet. It also included a secondary analysis to see if blood type had any effect on the outcomes, since, according to Dr. D’Adamo, only type A is supposed to thrive on a mostly plant-based diet. The researchers found that blood type made no difference in patient outcome. They also found that all blood types experienced improved weight loss and overweight adults experienced improvements in cardiometabolic health — from the diet change alone.
https://foodrevolution.org/blog/does-science-support-the-blood-type-diet/