D’Adamo says that protein components in food called lectins bind with antigens on blood cells and lead to blood cell clumping, or agglutination. Avoiding agglutination, D’Adamo argues, can improve health by helping people manage weight better and fight cancer and heart disease.Liz Weinandy, RD, at the Ohio State University Wexner Medical Center in Columbus, Ohio, says that lectins can be dangerous to our health if eaten in large amounts, but the way D’Adamo presents their effects may be misleading. Reducing their potential health harms is relatively easy: For example, lectins found in dried beans can be eliminated simply by soaking the beans in water for a few hours and then boiling them for 10 minutes, Weinandy says.But D’Adamo uses his theory to develop separate diets for people with blood types A, B, AB, and O. In addition, he recommends exercise and overall healthy habits, like drinking enough water, Weinandy explains. However, the diet is specific about which foods are allowed for different blood types — and that can be restrictive, Weinandy says.In fact, while people often have different nutritional needs, humans are complex animals, and chalking up these specifics to blood type may oversimplify those needs, Weinandy says. “To base a whole diet on that is probably not very sensible,” she says.