Characterizing Normal Bowel Frequency and Consistency in a Representative Sample of Adults in the United States (NHANES)

Am J Gastroenterol. 2018 Jan;113(1):115-123. doi: 10.1038/ajg.2017.213. Epub 2017 Aug 1.


Objectives: Our current understanding of normal bowel patterns in the United States (US) is limited. Available studies have included individuals with both normal and abnormal bowel patterns, making it difficult to characterize normal bowel patterns in the US. The current study aims to (1) examine frequency and consistency in individuals with self-reported normal bowel habits and (2) determine demographic factors associated with self-reported normalcy.

Methods: This study used data from adult participants who completed bowel health questions as part of the National Health and Nutrition Examination Survey (NHANES) in 2009-2010 and who reported normal bowel patterns (N=4,775). Data regarding self-perceived bowel health; stool frequency; stool consistency (using the Bristol Stool Form Scale (BSFS)); and demographic factors were analyzed.

Results: 95.9% of the sample reported between 3 and 21 BMs per week. Among men, 90% reported a BSFS between 3 and 5, while for women it was 2-6. After controlling for age, the following demographic variables were associated with normalcy: male sex, higher education, higher income, <2 daily medications, and high daily fiber intake. Hispanic ethnicity was significantly associated with abnormal self-reported bowel habits.

Conclusions: This is the first study to evaluate normal bowel frequency and consistency in a representative sample of adults in the US. The current findings bolster the common "3 and 3" metric of normal frequency (3 BMs/day to 3 BMs/week) while also suggesting different criteria for normal consistency for men and women. Finally, this study provides novel information about demographic factors associated with normal frequency and consistency.

Publication types

  • Research Support, N.I.H., Extramural

MeSH terms

  • Adult
  • Aged
  • Defecation*
  • Dietary Fiber
  • Educational Status
  • Ethnicity
  • Feces*
  • Female
  • Humans
  • Income
  • Male
  • Middle Aged
  • Nutrition Surveys
  • Reference Values
  • Sex Factors
  • United States
  • Young Adult


  • Dietary Fiber