A previous study on the same cohort of IBS patients showed a significant improvement in pain (P<0.001) and diarrhea (P<0.05) domains but not in constipation using Birmingham IBS symptom questionnaire after receiving dietary guidance compared with before guidance.34 It is possible that the significant changes in the cell densities of serotonin and PYY in IBS-D patients could be related to the observed symptomatic changes after receiving dietary guidance in the mentioned article. The gene discussed is PYY; the disease is irritable bowel syndrome.