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BLOG BY CHARLOTTE GREEN, BSC

The Link Between Food & Mood

The World Health Organisation has stated that mental health conditions, particularly depression and anxiety, are the number one cause of disability globally, affecting over 300 million people (1). Especially in these trying times, it has never been more important to look after and prioritise our mental health. Part of this is understanding how our lifestyle, including our diet, can influence the way we feel. For instance, a typical Western diet, which often contains high levels of saturated fat, sugar, and processed foods, can have a negative impact on both physical health and mood, making conditions like depression more likely (2). Conversely, following a Mediterranean style diet, which is centred around a diverse range of plant foods, complemented by smaller amounts of dairy, fish and healthy fats, can actually help to protect our mental health, and may even be useful as part of a treatment plan for depression (3).  

So, what is the link between food and mood?

Inflammation

Evidence has shown that depression is associated with chronic levels of inflammation in the body (4). One lifestyle factor that contributes to this is diet. A nutrient poor diet, such as the typical Western diet, is known to increase inflammation (2). Inflammation can have several negative impacts that affect our mental health including:

• Damage to the neurons in the brain, therefore increasing the risk of developing depression (2).

• An increase in circulating cytokines, which are chemicals released by the immune system that contribute to inflammation. They can modulate our emotions by affecting the release of serotonin and dopamine, our so-called ‘happy hormones’ (2). Cytokines can also affect the stress response, which can contribute to anxiety (5).

• Decreasing the volume of the hippocampus, a part of the brain involved in learning, memory, and mood (6).

However, there are certain foods that contain beneficial compounds that help to reduce inflammation and look after our mental health. One of the main compounds are polyphenols, a group of phytochemicals known for their anti-inflammatory and antioxidant properties (7). In this way, they are able to protect the neurons in the brain from damage caused by inflammation (8). Foods that are considered to be high in polyphenols include many fruits and vegetables, such as berries and spinach, coffee; and even dark chocolate, which has the added bonus of releasing endorphins when we eat it, helping to boost our mood (8).

The Gut Microbiota

Our intestines contain over 1000 different species of microorganisms, collectively known as the gut microbiota (9). They perform many essential functions in our body including digestion of nutrients, the production of vitamins and hormones, and are even implicated in our mental health. This is largely due to the gut-brain axis, which is the two-way communication between the gut and the brain (1). The gut microbiota contributes to this communication directly via the vagus nerve, through the cells of the immune system and by releasing chemicals into the blood (10).

The key to a well-functioning microbiota is diversity, yet it has been noted that people with depression often have a significantly less diverse microbiota, which could be contributing to the illness (11). There are many factors that affect the diversity of the microbiota, with diet playing an important role. A diet high in processed foods can often lead to a decrease in diversity as the microorganisms are not being sufficiently nourished to thrive (12). In turn, this increases a person’s chance of developing depression as a bacterial imbalance can cause inflammation (9).

However, the gut microbiota can contribute in positive ways to support our mental health. They produce several compounds during their metabolism, which are beneficial to our mood, including:

• Short chain fatty acids, which have anti-inflammatory properties (13).

• Tryptophan, an amino acid used to produce serotonin, a hormone involved in regulating mood, that is mainly produced in the gut (13).

As a result, it is very important that we nourish the trillions of microorganisms that reside in our gut to help protect our mental health. The main way we can achieve this through our diet is by trying to make it as varied as possible by including a range of fruits, vegetables, wholegrains, beans and legumes, and nuts and seeds. Remember, a diverse diet means a diverse microbiota.

The Mediterranean Diet

Although there is no one single diet that will guarantee good health, as nutrition is so individual, evidence does seem to point towards a Mediterranean style diet to help protect our mental health. For instance, the SMILES trial, showed that following a Mediterranean diet could even form part of a treatment plan for depression. In the trial, participants with diagnosed clinical depression were allocated to one of two groups. Alongside their medication, they were either guided through a Mediterranean style diet by a dietitian or given social support for 12 weeks. The study showed that the diet was in fact a more effective treatment strategy as this group experienced a more significant decrease in their depression symptoms (3). As a result, it is clear that food can really affect our mood.  

The Mediterranean diet is a traditional diet enjoyed in places like Italy and Greece, who are known for their good health and longevity. It is much more of a lifestyle than a simple diet, as it not only focuses on the wide variety of nutrients consumed, but also the importance of slowing down and enjoying food with family and friends. This principle is also particularly important for supporting our mental health.

The Mediterranean diet is a plant focused diet consisting of:

• A wide variety of fruits and vegetables

• Wholegrains, a source of complex carbohydrates to maintain sufficient energy levels

• Regular fish consumption, especially oily fish, which is higher in omega-3 fatty acids

• Extra virgin olive oil and other healthy fats such as nuts and seeds

•  Small amounts of lean meat and dairy

• Moderate alcohol consumption, with red wine being particularly beneficial (14)

The diversity of the Mediterranean diet is the key to its success in supporting our mental health, as no single nutrient in isolation is a miracle cure. It is high in polyphenols from fruits, vegetables, and red wine, which act as anti-inflammatories to protect the brain from damage, which is a risk factor for depression. Also, the high levels of dietary fibre help to nourish the gut microbiota (15). This is extremely important as the diversity of the gut microbiota plays a pivotal role in our mental health, due to its connection with the brain, via the gut-brain axis (1).

Overall, the key take-away from this article is that food can influence our mood, either positively or negatively. Therefore, one way that mental health can be supported is by consuming a well-balanced diet, loosely based around Mediterranean principles. However, treats should never be forgotten as these have a place in every balanced diet and certainly contribute to our mood.

This post was written by Charlotte Green who is a second-year undergraduate at Durham University studying Biological Sciences. She is fascinated by the gut microbiome and the role of nutrition in health, so hopes to pursue a Master's degree in Dietetics when she graduates. Charlotte is also part of The Ugly Fruit Group, a Durham based project aiming to tackle food waste by donating to food banks and creating healthy snacks from surplus fruit and veg. You can also find her on Instagram @charlottevictoria23

References:

1. Anderson S. (2019), How what you eat directly influences your mental health, New Scientist, viewed 15/10/20, https://institutions.newscientist.com/article/mg24332460-500-how-what-you-eat-directly-influences-your-mental-health/

2. Lassale, C., Batty, G.D., Baghdadli, A., Jacka, F., Sanchez-Vilegas, A., Kivimaki, M., Akbaraly, T. (2018), ‘Healthy dietary indices and risk of depressive outcomes: A systemic review and meta-analysis of observational studies’, Molecular Psychiatry, Volume 24, pp. 965-986

3. Jacka, F.N., O’Neil, A., Opie, R., Itsiopoulos, C., Cotton, S., Mohebbi, M., Castle, D., Dash, S., Mihalopoulos, C., Chatterton, M.L., Brazionis, L., Dean, O.M., Hodge, A.M., Berk, M. (2017), ‘A randomised controlled trial of dietary improvements for adults with major depression’, BMC Medicine, 15(23)

4. Carvalho, K.M.B., Ronca, D.B., Michels, N., Huybrechts, I., Cuenca-Garcia, M., Marcos, A., Molnar, D., Dallongeville, J., Manios, Y., Schaan, B.D., Moreno, L., De Henauw, S., Carvalho, L. A. (2018), ‘Does the Mediterranean Diet protect against stress-induced inflammatory activation in European adolescents?’ Nutrients, 10(11)

5. Kim, J.R., Kim, H.A., Song, S.W. (2018), ‘Associations among inflammation, mental health and quality of life in adults with metabolic syndrome’, Diabetology and Metabolic Syndrome, 10(66)

6. Jacka, F.N., Cherbuin, N., Anstey, K.J., Sachdev, P., Butterworth, P. (2015), ‘Western diet is associated with a smaller hippocampus: a longitudinal investigation, BMC Medicine, 13(215)

7. Firth, J., Marx, W., Dash, S., Carney, R., Teasdale, S.B., Solmi, M., Stubbs, B., Schuch, F.B., Carvalho, A.F., Jacka, F., Sarris, J. (2019), ‘The effects of dietary improvement on symptoms of depression and anxiety: A meta-analysis of randomised controlled trials’, Psychosomatic Medicine, 81(3)

8. Nehlig, A. (2012), ‘The neuroprotective effects of cocoa flavanol and its influence on cognitive performance’, British Journal of Clinical Pharmacology, Volume 75, Issue 3, pp. 716-727

9. Wang, B., Yao, M., Lv, L., Ling, Z., Li, L. (2017), ‘The Human Microbiota in health and disease’, Engineering, Volume 3, Issue 1, pp. 71-82

10.  Thomson, H. (2019), Healthy gut, happy mind: What to eat to boost how you feel, New Scientist, viewed 15/10/20, https://institutions.newscientist.com/article/mg24332460-600-healthy-gut-happy-mind-what-to-eat-to-boost-how-you-feel/

11.  Butler, M.I., Morkl, S., Sandhu, K.V., Cryan, JF., Dinan, T.G. (2019), ‘The Gut Microbiome and Mental Health: What should we tell our patients?’ Canadian Journal of Psychiatry, 64(11)

12.  Graf, D., Di Cagno, R., Fak, F., Flint, H.J., Nyman, M., Saarela, M., Watzl, B. (2015), ‘Contribution of diet to the composition of the human gut microbiota’, Microbial Ecology in Health and Disease, 29(2)

13.  Rieder, R., Wisniewski, P.J., Alderman, B.L., Campbell, S.C (2017), ‘Microbes and mental health: A review’, Brain, Behaviour and Immunity, 66, pp. 9-17

14.  Munoz, M.A., Fito, M., Marrugat, J., Covas, M.I., Schroder, H. (2009), ‘Adherence to the Mediterranean Diet is associated with better mental and physical health,’ British Journal of Nutrition, 101, pp. 1821-1827

15.  Rossi, M (2020), Nutrition and our mental health, The Gut Health Doctor, viewed 17/10/20, https://www.theguthealthdoctor.com/all-articles/nutrition-and-our-mental-health

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