Symptoms suggesting diseases of small and/or large intestine include abdominal pain, diarrhea, constipation, abdominal bloating, hematochezia, fever, weight loss, and/or others. It is important to analyze the predominant symptoms to avoid missing organic diseases. These symptoms reflect gastrointestinal sensation, motility, secretion, absorption, mucosal permeability, bacterial overgrowth in the lumen, and/or presence of organic diseases. The Bristol Stool Form Scale (BSFS) classifies stool shapes into seven types, from type 1 to type 7, to determine the presence of bowel abnormalities. Type 4 represents normal stool and is associated with the most comfortable defecation. Changes in BSFS numbers correlate more sensitively with gastrointestinal transit time than defecation frequency. Consequently, in the Rome III, Rome IV, and coming Rome V criteria for bowel disorders in disorders of gut-brain interaction (DGBI), a state where the proportion of BSFS type 1 or 2 exceeds 25% is considered constipation, and a state where the proportion of BSFS type 6 or 7 exceeds 25% is considered diarrhea. BSFS together with other patient-reported outcome (PRO) is not only useful for diagnosing and classifying the disease types of bowel disorders of DGBI but also serves as an evaluation method for determining treatment efficacy.