I had a yellow stool what is the most common cause of frequent yellow stools in a 16 year old?

Need more info: Normal stool color can vary greatly from brown to green to yellow. Yellow can result from a fatty meal, but could also indicate liver/gallbladder disease. Black, maroon, bloody, pale, white, clay colored stools or greasy/foamy/floating/mucus stools are all a cause for concern. Stooling frequency can also vary. More important than the #stools/day is a change in the normal pattern of stooling.