You've gotta see the guys JUMP on this one: I put a small cup (those tiny tupperware ones that I have no kids to use anymore) of food and one of water IN THE NEST BOX the last week. Mostly she ignores it, but I have seen her drink upon occation. But yes, Broody hens do lose a LOT of weight....my silkie is just skin and bones when hers finally hatch and she can just walk around and eat again. But she MUST be eating, based on the amount of poo that comes out when she does get off the nest each day to do so. She recovers just enough to do it again. I only give her eggs every other time she goes broody...partially for her health and a LOT so I am not hip deep in chicks. LOL
I do think that when they decide to go broody they start their fast and if we choose to wait a couple of day or weeks (or months for this silkie) they start losing from the moment they decide to go broody and sit until the chicks hatch. For the hen's health we should give them eggs the minute we notice they are broody. For our own mental health, we aren't going to do that, are we?