IBS to UC

IBS doesn't turn into UC. UC is an auto immune disease while IBS is a malfunctioning colon with irregular spasms. UC can be controlled thru diet modification, colon anti-inflammatory meds, steroids and immune suppression. IBS can be controlled basically by avoiding foods that bother you and/or taking an anti-spasmodics.

However, it's pretty common in UC'ers to have both IBS and an IBD.

A lot of things are "diagnosed" as IBS which turn out to be something else. Doctors see a lot of patients with digestive problems and tend to lump them into IBS because
(a) statistically many of them will indeed turn out to be a functional IBS
(b) doing all kinds of tests on everyone who comes in with stomach issues is impractical

But medicine's understanding of the digestive system is basically not much out of its infancy stages. As little as 10 or 15 years ago, spicy food and coffee was thought to cause GERD. Now they think it's due to h. pylori. Prior to 10 years ago, the small intestine was virtually ignored because it was so difficult to examine. Now with capsule endoscopy and breath tests for SIBO they're starting to look more at the small intestine.

As with anything in medicine, there are a lot of confounding variables, the digestive system is a complicated thing.