Written by Evangeline Mouratidis, Accredited Practising Dietitian, Sports Dietitian
Almost 50% of Australians will experience a mental health condition in their lifetime, while only around 5% of Australians meet their daily recommendations for fruit and vegetables (2 and 5 serves respectively). Coincidence or connection?
Regarding physical health, the negative impact of this diet is well-established. However the impact on mental health is less well known and understood.
Mood and Food
Depression is associated with a shrinking hippocampus, a region of the brain responsible for mood, memory and learning. A study led by Australian researchers found that people whose diets were richer in fruit, vegetables, and fish had larger hippocampi. Meanwhile those whose diets comprised mostly of processed and takeaway foods had smaller hippocampi. More importantly, this study also highlighted that these dietary patterns were linked an increased risk of depression over time.
How does the gut microbiome develop, and how does it affect my mood?
There is growing evidence showing that the diet of a mother during pregnancy may predict mental health problems in children. After studying more than 23,000 women and children in Norway, Australian researcher Professor Felice Jacka found that children of mothers who had unhealthier diets during pregnancy, displayed higher levels of behaviours associated with mental health problems during early years of life.
We know that the early years of life are also very important, as the gastrointestinal tract is rapidly developing and helping to shape our adulthood health. Of particular interest is the mode of birth (C-Section vs vaginal) and diet (formula vs breastfeeding) during those early years. Because food is what feeds and diversifies our gut microbiome, the introduction of solid foods and choice of food type also affects the health of the growing child’s microbiome.
Mood and Gut Bacteria
The role of the gut microbiome in the development and prevention of mental illness is a growing and exciting area of medical- nutrition research. We know the gut and the brain talk to each other through the bidirectional “gut-brain axis”.
We don’t yet know what the “perfect” mix of bacteria is in the gut. We do understand however that having a high level of diversity (or variety) of bacteria is linked to lower levels of inflammation and rates of certain diseases. On the other hand, low diversity is a marker of dysbiosis (bacterial imbalance) and has been associated with mental illness, autoimmune conditions, and cardiac diseases to name a few.
Your gut can also directly affect your brain’s signalling. Serotonin, a neurotransmitter found in the brain and mostly produced in the gut, has been extensively linked to depression and mood disorders when levels are low. Serotonin is the most common target of anti-depressant medications such as SSRIs.
Dysbiosis and inflammation are linked to depression.
The gut lining is home to around 80% of your body’s immune system, and your immune system is the driver of inflammation in the body. When you get sick, your fever and aches and pains are actually caused by your body’s own immune system as a response to a disease.
People with depression have been found with more inflammatory markers in the blood and were more likely to have an imbalance of gut bacteria. Though this creates a “chicken or the egg” scenario, studies show that a focus on improving gut health may be beneficial regarding mental illnesses such as depression and anxiety.
An unhappy, imbalanced gut-
- Increases the body’s stress hormones
- Decreases a growth factor called Brain Derived Neurotrophic Factor (BDNF). Low levels are often found in depression, bipolar disorder, and schizophrenia
- Promotes inflammation
Not all doom and gloom
While this paints a bleak picture, there is still hope! Animal studies have shown that fermented foods help to improve the symptoms of anxiety and depression. Unfortunately this has not yet been replicated in humans.
Probiotics may also provide a double benefit, with studies showing that Brain Derived Neurotrophic Factor levels (that growth factor from earlier), could be boosted with Bifidobacteria while also decreasing stress hormone levels. However, probiotics should not be used as a sole treatment of mental illnesses, and should instead be included alongside medical treatment.
Foods that are associated with poor mental health:
- Processed and takeaway foods which are often nutrient-poor and high in sugar and salt.
Foods that are associated with improved mental health:
Overall a mostly unprocessed diet, rich in plant foods and fibre.
- Olive oil
- Omega-3 rich foods (best sources are oily fish including: salmon, mackerel, anchovies, sardines, herring, trout)
- Wholegrains (such as brown rice, wholegrain bread, barley, farro, quinoa, buckwheat kernels, oats)
- Nuts and seeds
- Fermented foods
Fermented foods can be a source of both dietary probiotics and/or prebiotics. Some examples may include sauerkraut, kimchi, kefir, kombucha, and yoghurt.
- Eliminate harmful bacteria
- Create a better environment for good bacteria to grow
- Strengthen the immune system
- Produce anti-inflammatory Short-Chain Fatty Acids
- Produce Gamma Aminobutyric Acid (GABA) – beneficial for mental health
Most fermented foods and drinks are sources of probiotics.
Prebiotics are a type of fibre which cannot be digested. In the large intestine, specific types of good bacteria feed on these fibres to produce Short Chain Fatty Acids, which may decrease inflammation and promote the health of intestinal cells.
Prebiotics can be found in fibrous foods such as: some vegetables, fruits, legumes and wholegrains. Some of the best and most common sources are artichokes, asparagus, onion, garlic, banana, wholemeal bread, and lentils… just to name a few!
Traditionally fermented vegetables can be a source of both prebiotics and probiotics, when made with prebiotic-rich foods. One example of this may be kimchi which contains onion or garlic.
So not only does your diet affect your physical health, but there is convincing evidence that it affects your mental health too. While we typically think of depression as a problem of the brain, we shouldn’t forget that the gut can play a pivotal role both in the development and prevention of mental health problems. So instead of having a bucket of fried chicken every night, you might want to consider including more salmon, greens, and kimchi!
Evangeline is an Accredited Practising Dietitian and Sports Dietitian. She completed a Master of Dietetic Practice and Bachelor of Health Sciences at La Trobe University, and has further developed her skills by completing courses in Functional Medicine (AFMCP).
Evangeline is passionate about adopting a holistic approach in improving a person’s health and well-being. She aims to address the underlying causes of problems instead of adopting band-aid solutions.
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