Stool collection
Stool will be collected by participants 0–48 h prior to each of the three data collection visits using a kit provided by study staff. They will be instructed to store collected stool in a commercial refrigerator and to transport the stool on an ice pack to each visit. The stool will be stored in a refrigerator during the study visit. After the visit, it will be processed immediately for exfoliomics analysis (see below), with the remaining stool being aliquoted, flash frozen in liquid nitrogen, and then stored at −80°C until further analysis.