Fiber draws moisture from the colon and like a sponge, expands to increase the volume in your stool. This effect also occurs in your stomach and may create the feeling of being full. This is why when you consume high fiber foods, they tend to be more satisfying and you remain satisfied longer. Fiber will also help aid the colon during peristaltic contractions as a larger stool is easier for the colon to grip and move out of the body. Some soluble fiber will ferment inside the large intestine causing a release of methane and C02. This will cause the gut to bloat depending on the type of fiber and its fermentation and digestive characteristics.