Food Bloating

dreambig_gohome

How come, when I wake up in the morning, my stomach is flat, but by the end of the day it's not, no matter how little I've eaten? I know we all joke about "food babies". I've heard lots of theories, linked to high fiber, highs odium...etc. But I can bloat off of an apple. Is it just the ill effects of gravity and our digestive systems? What gives? Either way, it's frustrating.