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Is Your Gut Healthy?

Written by
Clare Carrick ANutr (BHSc Nutrition and Health Promotion)

Scientifically reviewed by
Dr Fathalla Ali, PhD (Paediatrics)


With all the talk about ‘gut health’ everywhere you look, you might be wondering what a ‘healthy’ gut even is! How can a healthy gut be measured? Is it just the absence of embarrassing or uncomfortable toilet symptoms, or is there more to it? 


Whilst the science of the gut microbiome is really still in its infancy in the scheme of things, researchers and scientists are gradually piecing together some important measures and interesting findings all about those trillions of tiny microbes that reside in your gut. One of the most important projects to do this is known as The American Gut Project (AGP), and the discoveries from this large study have helped add to our understanding of exactly what constitutes a ‘healthy gut’ (1).


The American Gut Project

The AGP was a crowdsourced, citizen science project (1). This means that people could volunteer to send microbiome samples, mainly from poop, to the folks running the project, and they’d get a full analysis of all the different types of microbes they’re hosting, whilst also contributing to a groundbreaking science experiment (1). Samples were collected from over 11,000 people, making it the largest microbiome database to date (1). The purpose of the project was to gain a better understanding of the microbiome, the different types of bacteria, and how a person’s lifestyle, diet and disease influence, or are influenced by, that person’s gut bugs (1). Let’s take a quick look at some of the most interesting findings…


Turns Out, You Don’t Need a Label

Society loves to give everything and everybody a ‘label’, but the AGP found that labels such as ‘vegan’ or ‘omnivore’ didn’t really mean anything when it came to representing a certain microbiome population (1). This makes sense…You can be vegan and eat fries, pizza and cola, or you can be vegan and eat a plant-rich, healthy diet… The best predictor of gut diversity was more to do with overall dietary quality than fitting neatly into any of these reductive labels (1).


It’s All About Plants

The number of different types of plants eaten over a week had the largest impact on the diversity of gut bugs (1). Participants who ate more than 30 different plant foods per week displayed significantly more gut diversity those who ate 10 or less plant foods (1). Those in the ‘30+ plant foods per week’ group also had more of the types of the bacteria that help to ferment Short Chain Fatty Acids (a good thing!), probably because, by eating an array of different plants, they were successfully feeding their gut microbes all the different types of fibre we know they love so much (1). We know that increased gut diversity is associated with better health outcomes across the lifespan, so these findings really help to back up the already existing advice to ‘eat more plants’! (1, 2).


Antibiotics and Gut Bugs

Antibiotics, whilst they can be necessary and life-saving, also significantly alter the composition of the gut microbiome. The AGP found that people who had had antibiotics in the last month had less diverse guts than those who had taken antibiotics within the last year (1). 


Interestingly, those who had taken antibiotics in the last month had greater gut diversity than those who had NOT taken any antibiotics within the last year, but they also had quite a different looking microbiome composition (1). This suggests that antibiotics completely change the types and amounts of microbes in your guts, but more thorough research needs to be done to draw conclusions from this (1). 


Again, eating 30+ plants per week had a positive effect on the gut, with the folks in the ‘30+ plants per week group’ displaying less antibiotic resistance genes than the people who ate less than 10 plants per week (1).


Mental Health and the Gut

One truly fascinating discovery in the AGP was that those who suffered from mental illness, specifically schizophrenia, bipolar disorder, PTSD, or depression, had a gut microbiome that more closely resembled others with mental illness than the participants without any mental health issues (1). Although more research needs to be done, this points to the link between the gut and the brain, and adds to the body of evidence supporting the need for diet and lifestyle to be addressed in the treatment of mental illness (3).

Keywords: Disease, Bifidobacteria, Diet/Nutrition,  Environment, Lifestyle


  1. McDonald D, Hyde E, Debelius JW, Morton JT, Gonzalez A, Ackermann G, Aksenov AA, Behsaz B, Brennan C, Chen Y, DeRight Goldasich L. American gut: an open platform for citizen science microbiome research. Msystems. 2018 May 15;3(3):e00031-18.
  2. Manor O, Dai CL, Kornilov SA, Smith B, Price ND, Lovejoy JC, Gibbons SM, Magis AT. Health and disease markers correlate with gut microbiome composition across thousands of people. Nature communications. 2020 Oct 15;11(1):1-2.
  3. Malhi GS, Bell E, Bassett D, Boyce P, Bryant R, Hazell P, Hopwood M, Lyndon B, Mulder R, Porter R, Singh AB. The 2020 Royal Australian and New Zealand College of Psychiatrists clinical practice guidelines for mood disorders. Australian & New Zealand Journal of Psychiatry. 2021 Jan;55(1):7-117.

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