> not to follow a fad who lasts a short time (which is essential to cargo culting).

Cargo cults are groups who follow rituals they don't understand: http://en.wikipedia.org/wiki/Cargo_cult

If a group is following a diet without understanding it, I think it's apt (though perhaps needlessly divisive) to call that group a cargo cult. If someone doesn't eat gluten and can't describe what gluten is and why it's bad, he or she is exhibiting the behavior of a member of a cargo cult.