I think the Fae binding thing is more a magical law of nature. They gave you something and are now entitled to get something from you in return. They might sometimes spike their food in addition, but since that can go against the rules of hospitality, that's probably not always the case.
Ectoplasmic food will probably dissolve too quick for you to be able to digest it. You might have better luck in the nevernever, where such things can persist for a longer period of time.
Fun fact, this was actually sort of my theory where the first Faeries might have come from. Some early humans stumble upon the nevernever and can't get out again, so they just settle down and live there. Since they are only eating nevernever food for generation after generation, food that is inherently magical, it slowly changes them to make them entirely magical creatures. The same is probably true for other types of animals.