...well, good question, not in the winter is the answer. Down here in the temperate rainforest, some people say that bears don't truly hibernate, it really isn't cold enough for them, but they do 'den' in the winter, a bit like some of us really.
A bear's metabolism changes, and they experience a lowering of body temperature, respiration and heart rate. They come into a wakeful state a couple of times a day and move around a little, but essentially, don't do much more than that. They use the calories from their fat to survive, since they don't eat during this period.
And the poop? Well, bears eat lots of tree bark and other roughage, and during the hibernation or denning, their anus becomes stoppered with faeces, hair, and discarded cells from their bodies! Although they do produce some small amount of faecal matter during the winter, this is recycled, in fact the nitrogen produced when their bodies recycle urea, helps to make protein.
If only we could do what bears do, we'd end the winter with less body fat and more lean tissue. And all of that whilst sleeping, although eating tree bark - meh, leave that for the bears methinks.