Donate Deakin
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Why is this important?
Depression and anxiety are so highly prevalent that they are considered ‘common mental disorders’ and are associated with poorer health outcomes and a decreased quality of life. Exciting research in the field of medical microbiology now focuses on the bacteria living inside our gastrointestinal system, known as our ‘gut microbiota’, and how these bacteria can impact health and disease, including mental and brain health. It is now recognised that we are able to influence our mental health by changing our lifestyle, such as diet, physical activity, sleep and other behaviours, and it is thought that the gut, and its resident bacteria, may be a key mediating pathway through which these factors are able to influence our mood and behaviour.

Considering the vast amount of evidence suggesting our gut is able to influence our overall health and mental health, it is important to also think about factors that may be affecting our gut health. A colonoscopy is a surgical procedure used to examine the inside of your gut. Before having a colonoscopy, patients have to take an extremely strong laxative, known as a ‘bowel prep’, to clear their bowels so that their doctor can see properly during the procedure. Studies have suggested that this bowel prep greatly influences our gut bacteria. Considering more than 800,000 colonoscopies are performed in Australia each year, it is imperative that we understand how this bowel prep influences our gut microbiota, and the potential influence on our gut and mental health.

How are we doing this study?
Our study was conducted in collaboration with Deakin University’s School of Medicine, University Hospital Geelong, and Epworth Hospital Geelong.

Patients requiring a colonoscopy were recruited from General Surgery and Gastroenterology clinics at University Hospital Geelong. Eighty-six patients completed a broad range of questionnaires related to physical health parameters, health behaviours and mental health, and they completed these questionnaires both one-week before and one-month after their colonoscopy. As part of standard procedure, all patients were required to take a bowel prep before their colonoscopy. Stool samples, which we use to measure the composition of the gut microbiota, were collected one-week before colonoscopy, after the bowel prep laxative, and one-month after colonoscopy.


Firstly, we will investigate how different aspects of physical health, health behaviours and the gut microbiota are associated with mental health symptoms through the creation of a hypothetical causal model. Results from this aspect of the study may provide insights into determinants of mental illness and suggest targets for treatment and preventive strategies for common mental disorders.

Secondly, we will investigate how the bowel prep process effects the composition of the gut microbiota, and subsequent gut health and mental health symptoms. Considering the number of colonoscopies performed each year, it is imperative that we understand the implications of the bowel prep on our physical and mental health.

Lastly, we will investigate how physical health parameters and health behaviours influence the re-establishment of the gut microbiota one-month after bowel prep for colonoscopy, which may inform future research into improvements in patient care post-colonoscopy.