Fecal incontinence (FI) affects 4-24% adults in the community and greatly impacts quality of life. Both fiber and loperamide are common, first-line treatments for diarrhea-associated FI in primary care. No known studies exist that compare fiber and loperamide for diarrhea-predominant FI. Further knowledge is needed to define which treatment is more effective and to compare drug tolerability (side effects) for FI. This study will also look at changes in quality of life with treatment and potential mechanisms of drug treatment.