The average human body carries ten times more bacterial cells than human cells

It’s funny how we compulsively wash our hands, spray our countertops and grimace when someone sneezes near us—in fact, we do everything we can to avoid unnecessary encounters with the germ world. The truth of the matter is that each and every one of us is a walking petri dish! All the bacteria living inside you would fill a half-gallon jug or 10 times more bacterial cells in your body than human cells, according to Carolyn Bohach, a microbiologist at the University of Idaho. Don’t worry, though. Most of these bacteria are helpful; in fact, we couldn’t survive without them.

For one thing, bacteria produce chemicals that help us harness energy and nutrients from our food. Germ-free rodents have to consume nearly a third more calories than normal rodents to maintain their body weight, and when the same animals were later given a dose of bacteria, their body fat levels spiked, even if they didn’t eat any more than they had before. The gut bacteria is also very important to maintaining immunity.