The American Gut Project – a global, crowdsourced citizen science effort – has published the first results from one of the biggest gut microbiome studies performed to date. 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.

Samples from each participant were analyzed using a variety of techniques to generate a broad picture of what bacteria was present in each unique microbiome. Metabolomics, shotgun metagenomics and the tracking of specific genetic markers all contributed to the comprehensive study of each sample. All subsequent microbiome data is de-identified and then placed onto an open source database for any researcher to utilize.

From initial observations, this first study focuses on three primary associations that the data has displayed. First, the study found that those participants who ate a large number of different plant types per week (30 or more) displayed a significantly greater bacterial diversity than those who ate a limited variety of plant types (10 or less). Interestingly, this observation carried through no matter what kind of individual diet a person consumed. So, that bacterial diversity was present whether they were a meat-eater or a vegan, as long as they consumed a large variety of plant types.

A second major observation was that consumption of antibiotics unsurprisingly resulted in a less diverse bacterial population. But it was also observed that participants consuming a large variety of plant types per week displayed less antibiotic-resistant genes than those who consumed fewer than 10 types per week.

This observation was somewhat unexpected, and the reasons are not particularly clear. The researchers hypothesize it may be explained by assuming those eating less plant products could be eating more meat from animals treated with antibiotics. This could be breeding a moderate volume of antibiotic-resistant bacteria.

The final significant observation from this paper examined associations between gut bacteria and mental health conditions. The data showed that people with mental health disorders, including depression, schizophrenia, PTSD or bipolar, had similar gut bacteria makeups. Specific bacteria types also tended to appear more commonly in people with depression.

The research was presented with a clear overview of its obvious limitations and the authors strongly note these are just observational correlations with no clear causal links suggested. The study adds that bacterial diversity, for example, doesn't implicitly equal better health, and simply eating more plants doesn't mean a person will become healthier due to effects on his or her microbiome.

Research into the broad effects gut bacteria have on a person's general health is still a nascent science, but Rob Knight suggests the more data projects like his can collect, the clearer a picture we can generate.

"The American Gut Project is dynamic, with samples arriving from around the world daily," says Knight. "The analysis presented in this paper represents a single snapshot, but we want eventually to go beyond making maps of the microbiome to making a microbiome GPS that tells you not just where you are on that map, but where you want to go and what to do in order to get there in terms of diet, lifestyle or medications."

With gut bacteria being found to possibly affect everything from Alzheimer's disease and diabetes, to aging and obesity, projects such as this one could be preludes to some of the biggest medical breakthroughs to come this century. Members of the public can participate in this massive citizen science project by visiting American Gut Project.

The study was published in the journal mSystems.