Understanding normal bowel habits in the general population is important for patients and physicians, but also for determining eligibility and outcome criteria in clinical trials. Using data from a nationwide survey in the USA, researchers have now analysed answers to health questions from adults reporting normal bowel patterns (n = 4,775). The majority of individuals (95.9%) reported a bowel movement frequency of 3–21 per week, upholding the common metric of normal frequency (three bowel movements per week up to three per day). However, different criteria for normal stool consistency, assessed using the Bristol stool form scale (BSFS), were found for men and women. Among men, 90% reported a BSFS of 3–5, but for women (90%) it was 2–6. Demographic factors associated with self-reported normalcy included male sex, higher education, income and fibre intake.
Mitsuhashi, S. et al. Characterizing normal bowel frequency and consistency in a representative sample of adults in the United States (NHANES). Am. J. Gastroenterol. http://dx.doi.org/10.1038/ajg.2017.213 (2017)
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Dickson, I. What are normal bowel movement patterns?. Nat Rev Gastroenterol Hepatol 14, 566 (2017). https://doi.org/10.1038/nrgastro.2017.124