Susannah Hollywood - 800 word feature article - created April 2024
Healthy gut, happy mind: how a well-balanced microbiome can influence our mental health
Evidence is mounting that processes in our digestive systems affect our physical health in numerous ways, due to a complex series of connections between our gut and the rest of our body.
Now early studies indicate a link between our gut and our mental health too, providing us with yet another reason to pay attention to our microbiome.
Our microbiome – what is it?
The community of micro-organisms (living things so small that they can only be seen under a microscope) that live on our skin and in our bodies are known as our ‘microbiota’. Each person’s is unique.
These micro-organisms, together with their habitat, are known as our ‘microbiome’ – a living, changing ecosystem.
In the gut, we have a microbiome containing trillions of microbes of thousands of different species.1 Most of these are bacteria.
What do these micro-organisms do in our gut?
Our microbiota breaks down food nutrients so that they can be absorbed into the bloodstream, create nerve signals, and produce vitamins, neurotransmitters and hormones.
They also defend against disease-causing organisms that arrive in the gut and play an important role in our body’s inflammatory response.
These important processes don’t just affect the gut, they impact the whole of the body, including the brain. Research suggests our microbiome is linked to many chronic conditions, including depression and generalised anxiety disorder, diabetes, cardiovascular disease and rheumatoid arthritis.2
The microbiota-gut-brain axis and mental health
Gut-brain communication is complex and uses many pathways in different systems of the body. Information passes via nerves and biochemicals in both directions – the gut influences the brain, and the brain influences the gut.
This connection is often known as the ‘gut-brain axis’ or perhaps more accurately, the ‘microbiota-gut-brain axis’.
This video from Science ABC explains more about the gut-brain axis
How the microbiota-gut-brain axis affects – and is affected by – our mental health is not fully understood. However, recent research indicates the link between the two.
A recent review of studies in this field, for example, concluded that people with mental health conditions have a different microbiota balance to those without, with lower levels of beneficial bacteria and higher levels of harmful, pro-inflammatory bacteria.
The analysis also showed that individuals with greater diversity of gut micro-organisms had lower depression scores.
In another study, researchers have been able to ‘transfer the blues’ by transplanting microbiomes from depressed humans into rats, which then developed behaviours associated with depression.
And diet was successfully used as a treatment for depression in the ‘Smiles trial’, significantly reducing symptoms in patients who increased intake of fruit, vegetables, whole grains and lean protein, and lowered intake of sugar and highly processed foods.
The microbiome in medicine of the future
Research into the microbiome and its influence on health is at an early stage and many more studies are currently underway.
Future study findings will hopefully bring clarity on how this connection can be utilised to improve diagnosis, prevention and treatments in a range of physical and mental health conditions.
“The medicine of tomorrow will come through microbiota”, concluded researchers in a 2022 review of studies in this field.
Microbiomes in the meantime: maintaining a good balance
In the meantime, there is a growing body of evidence to suggest that maintaining a well-balanced, well-nourished microbiota is beneficial to both our physical and mental health.
Researchers believe that we can benefit from increasing the population and diversity of micro-organisms in our gut, as well as nourishing them so that they function optimally.
To achieve this, we should include a wide range of both probiotics (foods with “friendly” bacteria, such as fermented foods) and prebiotics (a type of fibre that helps feed the good bacteria in your gut)
Early studies also suggest that our microbiome may be influenced by the medications that we take, our age, ethnicity and general health3 , as well as by sleep4, exercise5 and stress6.
Microbiota balance, it seems, is influenced by many factors.
Further research will hopefully improve our understanding of this complex area and allow us to harness the full potential of our microbiomes to positively influence our wellbeing, including our mental health.
Foods recommended for a healthy microbiota:
Probiotic foods:
live yoghurt
unpasteurised cheese
raw honey
fresh kimchi
fresh kombucha
fresh kefir
fresh sauerkraut
Prebiotic foods:
Fruits
Vegetables
Nuts
whole grains
legumes (beans and lentils)
References
1. Salvo-Romero E, Stokes P, Gareau MG. Microbiota-immune interactions: from gut to brain. LymphoSign Journal [Internet]. 2020 Mar [cited 2024 Mar 21];7(1):1–23. Available from: https://lymphosign.com/doi/full/10.14785/lymphosign-2019-0018
2. Vijay A, Valdes AM. Role of the gut microbiome in chronic diseases: a narrative review. Eur J Clin Nutr [Internet]. 2022 Apr [cited 2024 Mar 27];76(4):489–501. Available from: https://www.nature.com/articles/s41430-021-00991-6
3. Sasso JM, Ammar RM, Tenchov R, Lemmel S, Kelber O, Grieswelle M, et al. Gut microbiome–brain alliance: a landscape view into mental and gastrointestinal health and disorders. ACS Chemical Neuroscience [Internet]. 2023 May 5 [cited 2024 Mar 18];14(10):1717. Available from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC10197139/
4. Wu J, Zhang B, Zhou S, Huang Z, Xu Y, Lu X, et al. Associations between gut microbiota and sleep: a two-sample, bidirectional Mendelian randomization study. Front Microbiol [Internet]. 2023 Aug 14 [cited 2024 Mar 27];14. Available from: https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2023
5. Boytar AN, Skinner TL, Wallen RE, Jenkins DG, Dekker Nitert M. The effect of exercise prescription on the human gut microbiota and comparison between clinical and apparently healthy populations: a systematic review. Nutrients [Internet]. 2023 Mar 22 [cited 2024 Mar 27];15(6):1534. Available from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC10054511/
6. Cooke MB, Catchlove S, Tooley KL. Examining the influence of the human gut microbiota on cognition and stress: a systematic review of the literature. Nutrients [Internet]. 2022 Nov 2 [cited 2024 Mar 27];14(21):4623. Available from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC9656545/