Largest Ever Gut Microbiome Study Reveals New Insights into Health, Diet and Disease


American Gut Project – The Worlds Largest Study of Gut Bacteria Reports Findings for 11,000 Participants

The American Gut Project has released their findings after analysing the gut microbes of more than 11,000 participants providing fascinating insight into the complex relationship between gut bacteria, diet, lifestyle and human health.

The findings based on over 15,000 stool samples sent in from participants in the US, Canada, UK, Australia, Singapore and dozens of other countries around teh world – help further our understanding of the gut microbiome and the relationship between our gut microbial composition, diet, inflammation, mental health disorders and a huge range of chronic diseases.

The project based at UC San Diego School of Medicine – began collecting faecal samples from volunteers for analysis in 2012 and has since gained widespread interest and participation from around the world – to quickly become the worlds largest citizen science project.

“It’s really amazing that more than 10,000 members of the public want to get involved in science – [and]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.

 Courtesy of the American Gut project

The participants in the study sent in a stool samples for analysis together with voluntary surveys providing insight into their diets, lifestyle, health status, and history of illness. Of the 11,000 participants, 1,800 individuals also provided detailed images to illustrate their diet and frequency of eating habits.

The faecal samples, analyzed using a variety of techniques to determine which bacteria and microbes are present and in what quantities in each participants intestines. While there are still many strains of bacteria that are yet to be identified, the findings still provide a fascinating insight into the types and diversity of bacteria present in each participants gut.

The data collected by the Project have all been made publicly available after screening for any personal data, allowing insights and associations linked with the microbiota to be analysed and linked to factors such as diet, exercise, lifestyle, health and history of illness.

Notable Findings To Date:

Some of the most interesting findings to have emerged so far include:

Diets High in Different Vegetables Linked with Healthier Gut Bacteria

In line with previous understanding – a diet including many different types of vegetables (consisting of 30 or more different plant types each week) is correlated with a much higher diversity in their gut microbiota than participants with limited amount and variety of plant matter (10 or less) in their diet. A high diversity of gut bacteria is widely considered a sign of a healthy gut microbiome among scientists.

This pattern was noted irrespective of the type of diet consumed by the participant, greater bacterial diversity was seen in both meat-eaters and vegans, so long as they consumed a large variety of vegetables and plant matter.

Antibiotic Resistance

Participants with high plant diversity in their diet less likely to carry antibiotic resistant microbes

The participants who reported eating plant-rich fare (at least 30 types of plants per week) were less apt to carry bugs with antibiotic resistance genes compared to those who consumed 10 types of plants per week or fewer.

Another notable finding observed in people consuming many different vegetables each week was that they appear to fewer antibiotic-resistant microbes than people with fewer vegetables in their diet.

Some researchers speculate that these findings could linked with the use of antibiotics in farming livestock and food preservatives. Participants with less plant diversity in their diets may be consuming more meat and processed foods from antibiotic-treated animals and preservatives, which may be allowing antibiotic-resistant bacteria to thrive in place of non resistant bacteria affected by these chemicals.

Effects of Antibiotic Use in Farming

The participants who had taken antibiotics in the month prior to submitting samples had unsurprisingly less diversity in their gut bacteria than in other participants. However theses participants had much greater diversity in the types of chemicals in their gut samples than those who had not taken antibiotics in the past year.

However – Daniel McDonald, Scientific Director at the American Gut Project, noted something even more unexpected and disturbing. His team could detect agricultural antibiotics – those fed to animals like chickens and cows – in many people who claimed they hadn’t taken antibiotics in the year prior to their sample collection!

This suggests that antibiotics, used to fatten up animals raised in industrial farming could be reaching us through our food and harming the microbes in our gut.

Mental Health

Researchers also examined the microbiome samples from participants that had stated they suffered from depression or other mental health problems such as schizophrenia, bipolar disorder, or post-traumatic stress disorder.

The microbiomes of the participants with mental health conditions, were then matched for comparison with participants from the same location, of a similar age, gender and body mass index – but without any known mental health problems.

The findings revealed more similarities in the make up of the gut microbiomes in participants with mental health problems, than they did with their mentally healthy pairs. The researchers also found some specific types of bacteria were found to be more common in participants with depression than in mentally healthy people.

Find Out More

As our gut bacteria has been linked with all sorts of conditions ranging  from allergies to Alzheimer’, aging and obesity, to MS and Parkinsons, we can hope to hear about more exciting findings – particularly as the number of participants and samples continues to grow . Members of the public can participate in this massive citizen science project by

To find out more about the project and to participate visit American Gut Project or the British Gut.


About Author

John Cairn [BA] is a writer and food blogger, originally from the UK with a passion for food, travel and warm climates.