BACKGROUND: Hindgut symptoms are poorly understood complications of obesity. The impact of obesity on fecal incontinence (FI) and anorectal physiology remains unclear, with inconsistent results in prior studies. We aimed to evaluate the relationship between obesity and FI, and the physiological changes in anorectal function.

METHODS: This was a retrospective cohort study of consecutive adults who underwent high-resolution anorectal manometry (HRAM) at a tertiary center for anorectal symptoms. Demographics, clinical history, surgical/obstetric history, medications and HRAM findings were reviewed. Patients were classified as non-obese (BMI <25 kg/m2), overweight (BMI 25-29.9 kg/m2), class I obesity (30-34.9 kg/m2), and class II+III obesity (>35 kg/m2). Fisher-exact/student t-test for univariate analyses and logistic/general linear regression for multivariable analyses were performed.

RESULTS: 552 adults were included. Mean BMI was higher among patients with FI (27.5 vs 25.9 kg/m2, p=0.013). Compared to non-obese group, FI was more prevalent in class II+III obesity (31.7% vs 13.2%, p=0.0024), but not class I obesity or overweight groups. On multivariable analysis controlling for potential confounders, class II+III obesity (adjusted OR 2.89, CI:1.28-6.50, p=0.02) remained an independent risk factor for FI. Among patients with FI, both BMI (β-coefficient 1.09, p=0.016) and class II+III obesity (β-coefficient 18.9, p=0.027) independently predicted increased first rectal sensation volume on HRAM on multivariable regression.

CONCLUSIONS: Classes II+III obesity was an independent risk factor for FI. Among patients with FI, increasing BMI and class II+III obesity were associated with altered rectal sensitivity. Anorectal function testing should be considered to help guide management of FI among patients with obesity.