Diet and exercise have been established as contributors to human health, but less is known about how they interact to impact the gut microbiota. Based on scientific literature and evolutionary evidence, a combination of a minimally-processed fiber-rich diet and regular physical activity can benefit almost everyone. Diet and exercise affect one another; eating fiber-rich foods may increase the efficiency of physical activity and performing physical activity alters hormones that regulate food intake. This review explores the mechanisms by which diet and exercise affect one another as well as how they affect SCFA production, gut microbial diversity, and gut barrier integrity.