My biology teacher told the class about this one case in which some dude from the country came into the emergency room with bowel pain. They asked him when was the last time he defecated, and he said he hadn't in two weeks. When they asked him about his diet, he told them he had been drinking Mountain Dew for almost three weeks while eating little to no food. The nurses noticed his breathe was extremely offensive. His bowels had been backed up with feces, and some of it made its way into his esophagus. He went into emergency surgery and they had to clean him out, literally; his colon was very damaged.
When they looked at him his bowels were literally clogged up. Mountain Dew can indeed constipate the bowels, causing your colon to have problems.