User blog comment:Rafe Adler/"Let the Good Times Roll" Discussion/@comment-1031724-20180518164817/@comment-2020973-20180520142926

I doubt angels or demons need to eat or sleep to keep the host going.

Sam was able to sleep because like you said Gadreel wasn't controlling him at the time.

That is to say they are not incapable of it. For humans food and sleep are a requirement but for them it would be more like a luxury. Cas has explained that when he eats something he tastes that atoms but as a human the flavor is different and in a way more enjoyable.