BACKGROUND AND AIMS: Fecal incontinence (FI) is highly prevalent with substantial impacts on quality of life and healthcare utilization. The impact of obesity on FI remains unclear, with differing conclusions using BMI as risk factor. We aimed to determine the association between obesity and FI, and whether this relationship is dependent on the distribution of adiposity (waist circumference-to-height ratio, WHtR).

METHODS: This was a population-based analysis of the National Health and Nutrition Examination Survey, including participants who responded to the bowel health survey in 2005-2010. FI was defined by the accidental bowel leakage of solid stool, liquid, or mucus at least once in the past month. Stepwise multivariable logistic regression models were constructed to assess risk factors for FI.

RESULTS: A total of 7,606 participants were included, with an overall FI prevalence of 9.2%. When stratified by quartiles of body measurements, FI was increasingly prevalent from 1st to 4th quartile for both WHtR (range: 5.3%-12.5%) and BMI (range: 7.1%-10.5%). WHtR was associated with FI and was a stronger predictor than BMI in all quartiles of body measurement. On multivariable analysis, WHtR remained a significant predictor of FI comparing the 4th to the 1st quartile of body measurements (OR:1.77, CI:1.11-2.80, p=0.017), whereas BMI was not. A WHtR cutoff of >0.592 optimized the Youden index in prediction of FI in the overall sample.

CONCLUSION: WHtR was independently associated with increased odds of FI in this nationally representative sample of US adults, whereas BMI was not consistently correlated. This suggests bowel continence may depend more on how body mass is distributed.