I'd read before that many mammals lose more weight than bears during hibernation, but the weight they lose is a much more even distribution of different body ti

I'd read before that many mammals lose more weight than bears during hibernation, but the weight they lose is a much more even distribution of different body tissues. There's a lot of research on how bears are capable of burning almost entirely fat, while other animals would lose a lot of muscle and bone as well. A bear that isn't hibernating, IIRC, doesn't have this ability, so primarily fattening up in preparation for winter -- because that's all you need and it is more efficient -- may pose a problem if they start losing a lot of other tissues. But, presumably, if they were to lose more weight in winter be being awake than asleep, they'd just go to sleep. So they're probably not losing much more non-fat tissue. Bears AFAIK don't suffer ill-health effects like humans do from obesity. It's natural for a bear, so heart disease and diabetes would've been strongly selected against in bears, while suffering approximately 0 negative selective pressure among our ancestors.