POPULATION-BASED ANALYSIS OF STRUCTURAL DETERMINANTS OF FECAL INCONTINENCE USING QUANTIFIED AND PARTITIONED BODY COMPOSITION METRICS

Introduction
Fecal incontinence (FI) carries substantial health economic impacts with an estimated prevalence of 8% of the population globally. While the relationship between excess adiposity and FI has been inconsistently demonstrated, recent work from our group demonstrated a stronger association using body measures characteristic of centrally distributed adiposity. In this study we sought to determine whether these associations were due to excess adiposity as opposed to differences in muscle mass using highly accurate body measures determined by dual energy x-ray absorptiometry (DXA). Additionally we sought to substantiate whether the relationship between adiposity and FI was dependent on its body distribution.

Methods
This was a population-based analysis of the National Health and Nutrition Examination Survey (NHANES), an annual cross-sectional, nationally representative health survey. Surveys collected between 2005-2006 were analyzed due to inclusion of the bowel health survey and whole body DXA scans with body composition measurements in all eligible adult participants. Fecal incontinence was defined by accidental bowel leakage of solid stool, liquid, or mucus at least once in the past month. DXA parameters of interest included lean body mass excluding bone mineral content, total body % fat, as well as trunk (reflecting visceral adiposity) and leg % fat (associated with favorable metabolic profiles) stratified into quartiles. Sample weight adjustment was performed to account for complex survey design. Multivariable logistic regression models were constructed with adjustment for demographics, socioeconomic and dietary factors, and comorbidities.

Results:
4,308 participants were identified with responses to the bowel health survey. 2,795 participants were identified with both response to the bowel health survey and available DXA scan body composition measures. Baseline participant characteristics are summarized in Table 1. Overall prevalence of FI by body composition measure is presented in Figure 1. After comprehensive adjustment for covariates, total body % fat was a significant predictor of FI in the 3^rd (OR 2.07 [95% CI 1.03-4.16], p=0.042) and 4^th (OR 3.18 [95% CI 1.20-8.44], p=0.023) quartiles compared to the 1^st quartile. This relationship was preserved using trunk % fat in the 3^rd (OR 2.30 [1.03-5.17], p=0.044) and 4^th (OR 3.08 [1.26-7.52], p=0.017) quartiles. Conversely there was no significant association between leg fat % and FI (4^th quartile OR 1.54 [0.81-2.92], p=0.168). Quantified lean body mass was not a significant positive or negative predictor of FI.

Conclusion:
Viscerally distributed excess adiposity is a significant risk factor for fecal incontinence, and this relationship does not appear to be mediated by differences in muscle mass which may be obscured by traditional body measures like the waist circumference-height ratio or BMI.