Well there are theories that sleep is a form of hibernation of the human body to save resources. Building on that and on your Post id have some ideas why obesity takes place and so on. Note: I know some Fundamental Things about the medical field, but i am no expert:
The Mix of the over suppy of Food for a large portion of the developed countries leads to the general shortend sleep Duration. Also due to more and more people doing jobs in an office plus moving Less leads to a faster path to obesity. Also one important point is that (at least in my Region) most of the calories per Day are consumed in the evening which gives the cycle responsible for storage and processing (don't know the english synonym) loads of time Where the calories are not needed and due to that they get processed into storage forms (mostly fat).