Colorectal cancer (CRC) is the second leading cause of cancer-related deaths in the U.S. and is the third most common cancer in men and women. CRC risk factors include genetic predisposition, host factors and modifiable lifestyle behaviors (e.g., diet, physical activity, obesity). There are very limited data on the differences in the gut microbiota among populations at different levels of CRC risk, as well as the effects of behavioral interventions to alter the gut microbiome.