What is unspecified functional bowel disorder? A commonly seen, rarely recognized, and poorly understood diagnosis.

FBD-U, by Rome IV criteria, is highly prevalent in clinical settings. These patients are not represented in mechanistic studies or clinical trials for not having met Rome IV criteria for other FBDs. Making future Rome criteria less stringent would minimize the number fulfilling criteria for FBD-U and maximize the true representation of FBDs in clinical trials.