boldyloxx
That's a good question because the same thing happens to me.
I guess it may be that when we eat during the day, the food slowly moves through the intestines and pushes things out--- maybe even gasses are created that inflate the intestines-- pushing our stomachs out by the time night falls.
By next morning, digestion is complete- so that's when we get that bowel movement-- and our stomachs are flat again.
According to Barefoot Herbalist-- (and he may have a good point) He feels its better to eat one meal later in the evening--- and drink fluids throughout the day. The body is more effecient in digesting food when we are asleep. When are awake, our organs are not distracted trying to digest food- and we actually can have more energy that way-- as long as we eat towards evening and stay hydrated with raw fresh juices, herbal teas and water during the day. It sounds like it may work if we could get our body's used to doing that.