Perception of diarrhea and constipation differs greatly. This study aimed to correlate subjective and objective assessment of fecal characteristics in irritable bowel syndrome (IBS) patients.Data from two interventional dietary trials with varying FODMAP (Fermentable Oligosaccharides, Disaccharides, Monosaccharides And Polyols) or gluten content were interrogated. Subjects rated their dissatisfaction with stool consistency daily using a visual analog scale during the interventions. Subjects collected stools at the end of each intervention. Each stool was scored according to the King's Stool Chart (KSC). Fecal water content (FWC) was measured on pooled feces by freeze drying, with diarrhea defined as ≥78%.Seventy IBS (Rome III) and eight healthy subjects were studied. Each subject's self-rating of stool consistency during the most symptomatic diet was approximately double that of their least. Degree of dissatisfaction with stool consistency correlated poorly with changes in FWC and KSC. IBS subtype related poorly to objective measures of stool consistency. Sixty percent of IBS-D subjects had diarrhea on objective measures. Eighty-five percent with IBS-C had hard and formed stools but three patients met the criteria for diarrhea. One healthy subject had diarrhea on FWC and KSC, and six had hard, formed stools. No differences in FWC was observed when subjects consumed differing amounts of FODMAPs or gluten (all P > .200).There are major disparities between patients' stool descriptions and objective features of constipation and diarrhea. Patient-reported bowel habits require more interrogation for accurate IBS subtyping. Varying FODMAP or gluten content of the diet is not associated with consistent change in FWC.