honestly i was gonna say blood but then i remembered that that's vampires (though i think a fae vampire would be cool—they'd either be hilariously overpowered or hilariously weak)

but no, i thought about it and i'm thinking plant-life and such that are toxic/poisonous to humans. like mushrooms and flowers and parts of animals that humans can't eat. like fae are different species so they'd have different dietary requirements and it's pretty normal that they're very dangerous and more powerful then humans, so are they carnivorous, then? like a flowers that eat flies are carnivorous? or still omnivorous but with different tolerance to different things? (could they drink coffee?) or maybe even strictly herbivores, but with such different tolerances and requirements that it fools others into thinking they're omnivores?

i think i'll need to consider this some more...