A bird in space cannot eat. Birds have evolved with gravity and have never needed to develop a strategy to eat without it. Likewise, humans will also die without the stress of gravity. We would simply waste away.
There are many necessary stressors in life. Exercise, relationships, and the endless need to feed and protect ourselves. Without them, we would not be able to have all of the wonderful adaptations that we currently enjoy. Walking, healing, talking, and thinking would all be gone.