Aims: This paper aims to report the rationale, design, and the specific methodology of an ongoing nested observational study that will determine the association of the metabolite and microbial composition of stool with fecal incontinence (FI). Methods: Eligible cases are participants with FI enrolled in the Controlling Anal Incontinence in women by Performing Anal Exercises with Biofeedback or Loperamide (CAPABLe) trial, a Pelvic Floor Disorders Network trial across eight clinical centers in the United States. Women of similar age without FI in the last year served as controls. All subject collected stool samples at the baseline and 24-week visit at home using a standardized collection method. Samples were shipped to and stored at centralized laboratories. Results: Specimen collection commenced December 2014 and was completed in May 2016. Fecal water and DNA has been extracted and is currently being analyzed by targeted metabolic profiling for stool metabolites and 16S rRNA gene sequencing for stool microbiota. Conclusions: This article describes the rationale and design of a study that could provide a paradigm shift for the treatment of FI in women.