The purpose of this study is to determine the effect of dietary fat, in standard formulation, on the composition of the human microbiome in a prospective study of normal volunteers. Participants will be randomly assigned to either a high fat or low fat diet for 10 days. The gut microbiome will be phylotyped in fecal samples as well as in bacteria adherent to the colonic mucosa prior to, and during the course of the dietary interventions.