I've had difficulty finding anything reliable or well referenced.
Jersey, Channel Islands
Lectins are certain proteins -- and natural insectides! -- found in a variety of foods, including legumes, grains, dairy products, and some vegetables.
When consumed in certain quantities, they can cause severe gastrointestinal distress. It is also theorized that long-term lectin consumption can raise the risk for certain types of cancers.
However, cooking renders lectins inactive, so you are only vulnerable if you tend to eat certain foods (such as legumes or rice) in raw or undercooked forms.
Peter D'Adamo, author of The Blood Type Diet, blames lectins for a myriad of health problems.
According to Dr. D'Adamo, lectins can cause red blood cells to stick together and form clots if they are eaten by someone with a certain blood type.
How he came to such a conclusion completely escapes me (and all other Registered Dietitians I have ever spoken to), since there is absolutely nothing in the scientific literature substantiating his theories.
I don't consider lectins to be a health hazard since properly cooked foods don't pose any health risks in that regard.