I remember that, a few years ago, my parents were told that different blood types need to eat differently. From a quick look online, it seems to be called "Eat Right For Your Type."
It claimed that, depending on what your blood type is, some food groups should be preferred or avoided. For example, type O should prioritize meat and avoid wheat products; type A should prioritize vegetables and avoid meat. For a summary of the whole thing, see this article.
Is there any validity to those claims?