Modest Conformity Between Self-Reporting of Bristol Stool Form and Fecal Consistency Measured by Stool Water Content in Irritable Bowel Syndrome and a FODMAP and Gluten Trial

Am J Gastroenterol. 2022 Oct 1;117(10):1668-1674.doi: 10.14309/ajg.0000000000001942. Epub 2022 Aug 12.


Elise Nordin 1Per M Hellström 2Carl Brunius 1Rikard Landberg 1


Author information

1Department of Biology and Biological Engineering, Food and Nutrition Science, Chalmers University of Technology, Gothenburg, Sweden.

2Department of Medical Sciences, Gastroenterology/Hepatology, Uppsala University, Uppsala, Sweden .


Introduction: Altered bowel habits constitute a criterion of irritable bowel syndrome (IBS), with the Bristol Stool Form Scale (BSFS) as the recommended tool for assessment of fecal consistency. However, BSFS is devoid of a comprehensive objective evaluation in subjects with IBS. Therefore, we aimed to evaluate the concordance between subjective reporting of BSFS and objective stool water content in subjects with IBS. Furthermore, we evaluated whether intake of fermentable oligosaccharides, disaccharides, monosaccharides, and polyols (FODMAPs) or gluten would affect stool water content.

Methods: Data from a previous crossover trial in IBS with 1-week provocations of FODMAPs, gluten, or placebo were subanalyzed. After each intervention, fecal consistency was subjectively assessed using the BSFS and stool samples were collected. The stool water content was analyzed, where ≤68.5% water content was classified as hard stool, while ≥78% was classified as diarrhea.

Results: BSFS correlated to stool water content ( r = 0.36, P < 0.0001). The BSFS score increased in parallel with increasing water content, but with considerable overlap between BSFS scores. Stool water content differed between the BSFS categories 1-2, 3-5, and 6-7 (hard, normal, and loose, respectively) ( P < 0.0001). For BSFS categories 1-2, 77% had water content ≤68.5%, whereas for BSFS categories 6-7, 52% had water content ≥78%. There was no difference in stool water content after consumption of FODMAPs, gluten, or placebo ( P = 0.94).

Discussion: Subjective reporting of BSFS conforms only modestly with stool water content in IBS, warranting caution when subtyping IBS according to the BSFS. High intake of FODMAPs and gluten does not affect stool water content.

Trial registration: ClinicalTrials.gov NCT03653689.


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