Written by Lucy Walton
It’s well established that what we eat can affect our physical health, but there is also research to suggest what we eat can affect our mental health and wellbeing too.
At a basic level, eating a well-balanced diet high in fruit and vegetables has been associated with feelings of wellbeing. One 2014 study found high levels of wellbeing were reported by individuals who ate more fruit and vegetables (1). But we can delve a little deeper into the research and also see there’s more to it.
There is continuous evidence pointing towards the Mediterranean diet (MD), a dietary pattern which has been linked to helping to protect mental health. The MD is high in fruits, vegetables, wholegrains, nuts and olive oil. It also contains moderate amounts of eggs, dairy, poultry, legumes, potatoes and fish (particularly oily fish) while limiting intake of sweets, red and processed meats. The intake of polyphenols from fruit and vegetables are thought to protect the brain from damage due to anti-inflammatory properties and the high fibre content helps to nourish the gut microbiota (GM).
The Smile’s Trial (2017) compared a nutrition intervention focusing on mindful eating and the MD to a social support treatment. Those in the dietary support group demonstrated a greater reduction in depressive symptoms compared to the control group (2). Suggesting dietary improvement may provide an effective treatment strategy for depression. It should be noted that during the trial participants remained on medication.
Another study found a Mediterranean style diet supplemented with fish oil led to a reduction in depression among participants, which was sustained six months after the intervention (3). This is interesting, as although there is no single nutrient in isolation that can provide a miracle cure to mental or physical health, omega-3 fatty acids, found in oily fish have been linked to improved mental health outcomes. Hsu et al (2020) found omega-3 fatty acid supplementation reduced psychotic symptom severity and improved both positive and negative symptoms of schizophrenia (4).
Omega-3 polyunsaturated fatty acids have also been linked to inflammation and depression; depression appears to be less common in nations where people eat large amounts of fish (5,6,7,8). However, this is only observational data and evidence of this from randomised controlled trials is mixed. Having said that, Kiecolt–Glaser et al 2011 found a reduction in anxiety symptoms in student participants that were supplemented with omega-3 compared to a placebo group (9).
A 2016 meta-analysis of 26 studies also found a 17% lower risk of depression with higher fish intake (10). A second meta-analysis of over 1000 people found that supplementing with omega-3 was helpful in reducing depressive symptoms, eicosapentaenoic acid (EPA) ≥ 60% at a dosage of ≤1 g/d (11). The mechanism is thought to function due to the accessibility of omega-3 to travel through the brain cell membrane and interact with mood-related molecules, influencing neurotransmission and prostaglandin formation (12). Their anti-inflammatory actions are also noted to have an effect (5).
Links between food and the brain go further, the diversity of the gut microbiota plays a pivotal role in our mental health, said to be due to the connection between the brain and the gut via the gut-brain axis. The gut-brain axis is a two-way communication between the brain and the gut which uses hormones and other messengers to manage what we do and how we feel. A healthy GM contributes to effective communication between the gut and then brain, via the vagus nerve, through the cells of the immune system and by releasing chemicals into the blood stream. It has been found that individuals with depression have a significantly less diverse GM (13), which is thought to cause bacterial imbalance, leading to inflammation (14). Evidence also shows that inflammation negatively impacts mental health by damaging neurons in the brain and affecting the release of serotonin and dopamine (our ‘happy hormones’). A diet that is made up of a variety of plant foods and limits processed foods benefits the gut. Processed foods can often lead to a decrease in diversity of the gut microorganisms due to lack of nourishment, increasing the risk of inflammation (15).
The gut microbiota can also support mental health through production of short chain fatty acids, which have anti-inflammatory properties and are beneficial to mood. Tryptophan is also produced which assists in the production of serotonin, involved in regulating mood (16).
Let’s remember, there are a range of inequalities that contribute to the development of mental health problems, this is a very multi-faceted issue. Factors such as physical activity, living in poverty, income, environment, sleep, stress, physical health, to name just a few, all have a role. Nutrition is just one area we can look at to see if relationships are present.
Overall evidence suggests there is a link between the food we eat and mental health, including a Mediterranean style diet which is diverse in plant foods and high in omega-3. The relationship between our brain and gut via the gut-brain axis is an important mechanism. A diverse diet contributes to a diverse gut which positively impacts the connection between our brain and gut, keeping both happy.
References
- Stranges et al (2014) https://bmjopen.bmj.com/content/4/9/e005878
- Jacka et al (2017) https://bmcmedicine.biomedcentral.com/articles/10.1186/s12916-017-0791-y?mod=article_inline
- Parletta et al (2019) https://pubmed.ncbi.nlm.nih.gov/29215971/
- Hsu et al (2020) https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7333328/#Abs1title
- https://www.health.harvard.edu/blog/omega-3-fatty-acids-for-mood-disorders-2018080314414
- Wani et al (2015) https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5481805/
- Hegarty and Parker (2013) https://pubmed.ncbi.nlm.nih.gov/23108232/
- Golding et al (2009) https://pubmed.ncbi.nlm.nih.gov/19289957/
- Kiecolt-Glaser et al (2011) https://www.sciencedirect.com/science/article/pii/S0889159111004685?casa_token=10vJvRfKjaoAAAAA:InC0u1ZZhkuyAmHkRBacvn1segf8QEJw_uUXxoTWBBP3TP8wFC0hx1jP2x-LzaGpzpEgAythDkM
- Li et al (2016) https://pubmed.ncbi.nlm.nih.gov/26359502/
- Liao et al (2019) https://www.nature.com/articles/s41398-019-0515-5
- Haag (2003) https://pubmed.ncbi.nlm.nih.gov/12728744/
- Butler et al (2019) https://journals.sagepub.com/doi/full/10.1177/0706743719874168
- Wang et al (2017) https://www.sciencedirect.com/science/article/pii/S2095809917301492
- Graf et al (2015) https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4318938/
- Rieder et al (2017) https://pubmed.ncbi.nlm.nih.gov/28131791/
- NIH omega-3 Fatty Acids fact Sheet https://ods.od.nih.gov/factsheets/Omega3FattyAcids-HealthProfessional/