The complex digestion process ensures that almost no useful energy goes unused. The average bowel movement is three parts water to one part solid matter. Bacteria make up 30 percent of the solid stuff. The same goes for indigestible foods like cellulose and extra fiber. The remaining 40 percent contains various inorganic wastes, fats and used-up body substances like red blood cells

Aiding the large intestine in this task are trillions of microbes that reside in the gut, where they help digest foods we would otherwise have to avoid. In this way the bugs contribute to our overall health.

Some of these tiny settlers are with us from birth, imparted from our mothers, while others gradually colonize our bodies as we grow. This microbial community is as diverse as any found in Earth’s seas or soils, numbering up to 100 trillion individuals and representing more than 1,000 different species.