"The field of microbiota and health took off in 2006, when scientists led by Jeffrey Gordon of Washington University in St. Louis noticed something: Fat mice and svelte mice have very different gut microbes. Could different microbes actually cause obesity? To find out, Gordon transferred gut bacteria called Firmicutes from obese mice into thin ones. The thin mice ate no more than they used to, but they quickly started packing on the pounds (okay, ounces). Firmicutes, it turns out, are really good at liberating calories from food, much better than the common gut bugs called Bacteroidetes."
How germs help us stay healthy | Grand Forks Herald | Grand Forks, North Dakota