Problem that cannot be pinpointed

My mom has had a really weird stomach problem for about 10 months. One day, she woke up and had different colored stools. The stools started out with firm and soft stools together. They became lighter tan, and afterwards yellow. Sometimes the stool is more firm than others, always firm, always yellow. She was confirmed to have IBS with rapid transit because they ruled everything else out, but she never had any pains that are said to be included in having IBS. She has had every Gastroenterology test, small bowel series, colonoscopy, stool sample, bloodwork, catscan, but they cannot find inflamation (inflammation), or anything that could lead them to a solution, however, gallbladder was never checked. She also doesn't eat any yellow pigmented food to make the coloration of food yellow. In the summer, she had undigested food, but hasn't had it in a while. She's on a strict IBS diet now, taking acacia fiber. She also hasn't tried any questrin for bile output, which she thinks could also be something to do with why her stools are yellow. Does IBS sound right? Is it possible it's something else? Are there any other tests she could she have done? Thank you!

[CalGal]

If her stools actually turned a lighish color - very, very light tan to whitish - then it's probably related to the amount of bile she's putting out. Bile is the substance that gives the stool it's normal 'brown' color. It's secreted as a yellowy-green and as it's worked on by the digestive enzymes and passes through the GI tract, it turns the brown we're all familiar with. When bile isn't secreted to mix with the food contents, then the fecal material will end up being whitish.

If her stools goes whitish again, make sure she gets checked and have both liver and pancreatic enzyme levels checked at that time. It could indicate that she might be having spasms of the biliary system or that her GB is not working correctly.