The study is only observational, fueled by self-reports from participants, but it offers a compelling snapshot into the complex relationship between gut bacteria and human health.

The study is a perfect example of citizen science, a burgeoning scientific model that recruits the general public in contributing to valuable data collection and research. The American Gut Project began in late 2012, gathering fecal samples from participants all over the globe. Accompanying each sample, participants were asked to complete a survey to gain insight into their lifestyle, diet and general health.

"It's really amazing that more than 10,000 people – members of the public who want to get involved in science whether or not they work in a lab or have a PhD – have mailed their poop to our lab so that we can find out what makes a difference in somebody's microbiome," says Rob Knight, one of the co-founders of the project.