My big male, Goblin, has not eaten since valentines day. But I really see no weight loss at all. In fact, even prior to that feeding, he seemed to be almost a bit overweight. He is pictured in my Avatar, incidentally.
How often do your big males really eat? I offered him a prekilled rat a few weeks ago, which turned into a f/t rat the next week (hehe.) and he is not at all interested.