Bacteria and Human Body Cells

The human body contains roughly similar numbers of bacterial and human cells, not ten times as many bacteria as often repeated in the past. A 2016 estimate for a reference 70-kg adult male was about 38 trillion bacteria and 30 trillion human cells; the ratio varies among people and depends in part on body mass and gut contents. Most bacteria live in the large intestine. Some help ferment dietary fiber into short-chain fatty acids and influence the gut barrier and immune processes.