That happens to everyone.
If you want to test it, drink a liter of soda, or a liter of chocolate milk. You'll balloon in a few hours. It'll disappear the next day.
There's not a lot you can do, since almost every food has some sort of byproduct (ie. when you digest something, it releases gas). Those guys that takes photos with rock-hard abs, don't have those abs 24/7. You probably saw it in the sticky already, bodybuilders are at their weakest during competitions.
But it's not such a foolish question. Some user came here and asked why he couldn't get rid of his rolls of fat that only appeared when sitting down, and people replied: "that's not fat, that's your skin and tissues - there's almost no way to look "ripped" while sitting down".
