3. Intestines can hold something like 7Ibs (mabe more not sure on #s any more) of food at any given time. When cutting there not usually that full since your usually in a food deficit, while bulking however consider that your intestines may be saturated w/ all the food you eat. If you think about it 7Ibs of food in your intestines have to make your stomach bulge out a bit.]
4. When bulking I know many people whom drink less water unknowingly, simply because they are full most of the time, and hunger/thirst are often very similar feelings. Plus when dieting people tend to drink more to sastisfy themselves a bit more. (add another for possible water retention)
5. The muscle that holds you abdominal wall inward (forgot its name) may be tired since you have more weight in your stomach (full stomach saturated intestine) It could be fatigued and causing it to not do its job quite as well.
Its from all the extra food stored in ur tummy. Have you noticed that when you wake up in the morning, your stomache is smaller, but later on the day it gets larger? Its definitely from the food, plus ur bulking, so ur bound to put on a little fat