Could Our Food Be Influencing Our Mood?
When we think about mental wellbeing, we often focus on factors such as managing stress, getting enough sleep, being active, and maintaining social connections. While all of these are fundamental to supporting our mental health, we may have been missing another piece to the puzzle, our gut health. The link between food and mood is an exciting area of research, with emerging evidence suggesting that the foods we eat may influence our mental wellbeing through a complex communication network known as the microbiome-
gut-brain-axis.
Did You Know?
Your digestive tract is home to trillions of microorganisms, including bacteria, viruses, and fungi, collectively known as the gut microbiota. While we often think of these microorganisms as harmful, many are essential for good health. Our gut microbiota play vital roles in digestion, immune function, disease prevention, and maintaining gut health. Optimal gut health is generally characterised by a diverse and balanced gut microbiota, where beneficial bacteria are present in greater abundance than harmful (opportunistic)
bacteria (PMID: 39322314).
The Microbiome-Gut-Brain-Axis
The microbiome-gut-brain-axis is a constant, bidirectional communication pathway between the gastrointestinal (GI) tract and the brain. The large community of microorganisms living within our gut is thought to play an important role in modulating this communication network, and scientists are becoming increasingly interested in how changes in the gut microbiota may influence brain function and mental health. As diet is a key factor in shaping the composition and function of the gut microbiota, researchers are now investigating whether dietary strategies that support gut health may also help support mental wellbeing.
What Does the Research Say?
Over the past decade, interest in the relationship between diet, the gut microbiota and mental health has grown considerably. Observational studies have consistently reported that Mediterranean-style diets (MedDiet), rich in fruits, vegetables, fish, nuts, and olive oil, are associated with a lower risk of depression and higher levels of happiness, life satisfaction, and overall wellbeing compared with more highly processed dietary patterns. These findings have prompted researchers to investigate whether improving diet quality can
directly influence mental health outcomes.
One of the first large clinical trials to do this was the SMILES trial, which investigated whether improving diet quality over 12 weeks could support adults experiencing moderate to severe depression. Participants who adopted a Mediterranean-style dietary pattern experienced significantly greater improvements in depressive symptoms and higher remission rates than those receiving social support alone (PMID:28137247). Another intervention study investigated the effects of a Mediterranean-style diet in 612 older adults across five European countries (PMID: 32066625). After one year, participants developed a
more favourable gut microbiota profile, characterised by an increase in health-promoting bacteria that was associated with improvements in frailty markers and cognitive function. As interest in the gut-brain connection has grown, researchers have also begun investigating whether directly altering the gut microbiota through faecal microbiota transplantation (FMT) could influence mental health outcomes. A 2020 systematic review examined preclinical and clinical studies investigating FMT in psychiatric disorders (PMID: 32539741).
Across the studies, the transplantation of healthy microbiota into individuals with psychiatric disorders resulted in reductions in depressive and anxiety-like symptoms and behaviours. Interestingly, the reverse was also observed, with transplantation of microbiota from psychiatrically ill donors to healthy recipients associated with the transmission of depressive and anxiety-like symptoms and behaviours. While these findings are promising, larger human clinical trials are still needed before FMT could be considered a therapeutic
approach for psychiatric disorders.
Putting the Evidence into Practice
So, what do these findings actually mean in practice? Although research into the microbiome-gut-brain axis is still evolving, current evidence does suggest that supporting a healthy gut microbiome may be one practical way to support healthy communication between the gut and brain. While no single food can optimise gut health, research consistently points towards an overall diverse dietary pattern, rich in a
variety of plant foods, as the most effective dietary approach.
Aim for 30 Different Plant Foods Each Week
One of the simplest and most consistent findings to emerge from gut health research is the benefit of increasing plant diversity. Research from the American Gut Project found that individuals who consumed 30 or more different plant foods each week had significantly greater gut microbial diversity than those consuming fewer than 10 (PMID: 29795809). Eating a greater diversity of plant foods provides our gut bacteria with a wider range of fibre and other beneficial compounds, including prebiotics and phytochemicals. As these compounds are fermented by the gut microbiota, they produce short-chain fatty acids, which help regulate inflammation, and support gut health, and immune function.
Importantly, plant foods include much more than just fruit and vegetables. Wholegrains, beans, lentils, peas, nuts, seeds, herbs, spices, coffee, green tea, olive oil and even dark chocolate all contribute towards your weekly total. Rather than aiming for all 30 at once, focus on gradually increasing the variety of plant foods you eat. For example, a breakfast of coffee, wholegrain oats, blueberries, chia seeds, walnuts and cinnamon already contributes six different plant foods towards your weekly goal.
A Psychobiotic Diet
The role of fermented foods in supporting gut and mental health is also an area of growing scientific interest. A 2021 dietary intervention study compared the effects of a high-fibre diet with a high fermented food diet (PMID: 34256014). Participants who increased their intake of fermented foods developed greater gut microbial diversity alongside reductions in several markers of inflammation, while those following the high-fibre diet demonstrated improvements in the functional capacity of their gut microbiome.
Building on these findings, researchers have proposed the concept of a psychobiotic diet, a dietary pattern rich in both prebiotic fibre and fermented foods that aims to support the microbiome-gut-brain axis. A 2022 intervention study in healthy adults found that participants following a psychobiotic diet reported greater reductions in perceived stress than those consuming a control diet, and those who adhered more closely to the diet experienced the greatest reductions.
Together, these findings suggest that fibre and fermented foods may provide complementary benefits for supporting a healthy gut microbiome. Fibre feeds and nourishes beneficial gut bacteria, while fermented foods may help promote greater microbial diversity. Although more research is needed to better understand the underlying mechanisms, regularly including fermented foods such as natural yoghurt, kefir, kimchi, and
sauerkraut, alongside a variety of fibre-rich plant foods may be a practical way to support a healthy gut microbiome and, in turn, the communication between our gut and brain.
The Take-Home Message
Although research into the microbiome-gut-brain axis is still evolving, growing evidence suggests that the foods we eat may influence much more than just our physical health. While mental health is complex, and nutrition should never be viewed as a replacement for appropriate medical or psychological support, this research has helped reveal that dietary strategies may play an important complementary role as part of a broader approach to psychological wellbeing. The good news is that our gut health is something we have the opportunity to support every day simply through the foods we eat. Focus on building a plant-forward dietary pattern that includes a wide variety of fibre-rich and colourful plant foods, alongside fermented foods. Small changes, made consistently over time, can add up to make a meaningful impact on both your gut health and overall wellbeing.