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'Normal' bowel habits differ between men, women

Anthony Lembo



For the first time, researchers characterized normal bowel habits for adults in the United States.

For normal bowel frequency, they confirmed the commonly accepted “3 and 3” metric — a range of three bowel movements per day to three bowel movements per week — and for normal bowel consistency, they found that men and women showed different criteria. Further, they identified key demographic risk factors for abnormal bowel habits, which notably included Hispanic ethnicity.

“Since estimated prevalence of functional gastrointestinal disorders such as constipation and diarrhea range up to 20% and 17%, respectively, it is essential to evaluate a sample of individuals without reported constipation or diarrhea in order to understand normal bowel function in the general population,” Anthony Lembo, MD, of the division of gastroenterology at Beth Israel Deaconess Medical Center and Harvard Medical School in Boston, and colleagues wrote.

To do so, Lembo and colleagues assessed data from 4,775 adult participants in the National Health and Nutrition Examination Survey in 2009-2010 who reported normal bowel habits (age range, 20-70+ years; 52% men; 50% white; 50% with at least a high school education). They analyzed demographic data, self-perceived bowel health, and stool frequency and consistency.

Most of the participants (95.9%) reported a frequency of 3 to 21 bowel movements per week. In detail, 2.7% reported fewer than three bowel movements per week, 60.5% reported 3 to 7, 29.9% reported 8 to 14, 5.7% reported 15 to 21, and 1.4% reported more than 21 per week.

Regarding consistency, 86.2% reported a Bristol Stool Form Scale (BSFS) type of 3 to 5 overall, but while the 5th to 95th percentile of men reported a BSFS type between 3 to 5, the 5th to 95th percentile of women reported a BSFS type between 2 to 6.

“For both women and men, the percent reporting self-perceived normal bowel habits was negatively related to age,” Lembo and colleagues wrote. “Overall, men more frequently reported normal bowel habits than women.”

Further, after controlling for age, they found that male sex, higher education and income, lower number of daily medications (fewer than two), and high daily fiber consumption (higher than 20.1 g) were all associated with normal bowel patterns. The discrepancies in bowel habits based on education, ethnicity and income may be explained by dietary differences related to these variables, the investigators suggested.

Conversely, they found that thyroid problems and Hispanic ethnicity were associated with abnormal bowel patterns.

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They found no significant differences in bowel habits related to BMI, smoking, caffeine intake or physical activity, although when analyzing men and women separately, they found vigorous physical activity was associated with normal bowel habits in men only (P = .02).

“These findings contribute to existing literature by bolstering the common ‘3 and 3’ metric of normal bowel frequency ... however, they also suggest that men and women should have different criteria for normal bowel consistency,” Lembo and colleagues concluded. “In addition to confirming metrics for normalcy, this study also provides novel information about demographic factors associated with normalcy when considering frequency and consistency of BMs in the general U.S. population.”

The investigators noted that many participants who reported diarrhea or constipation fell within the normal range of bowel frequency and consistency in this study, which highlights the variation in individuals’ interpretation of what is considered normal.

“These two groups also reflect differences in likelihood to seek treatment for constipation/diarrhea, and may indicate some amount of hypervigilance or hypersensitivity to bowel habits in the group who reported diarrhea or constipation always or most of the time,” they wrote. “These findings can be used clinically in order to normalize frequency and/or consistency in patients presenting for treatment of constipation or diarrhea.” – by Adam Leitenberger

Disclosures: The researchers report no relevant financial disclosures.