Like the giant panda, they need a LOT since they can't digest cellulose. You kind of have to wonder just how "good" mother nature is to have an animal evolve to have a diet of a material that it can't digest very well.
Plus bamboo doesn't have much of a caloric value so they have to eat lots of it. You'd think they'd evolve to increase their diet of better food.
I'm actually surprised people haven't attempted to domesticate these critters. I know I'd have one in a heart beat. they seem like real characters although their being nocturnal by nature would be a bit of a pain lol.....