This fascinating guest post was written by Katie O’Callaghan. She is a final year dietetics student based in London. Katie is passionate about evidence-based nutrition and believes in a balanced and holistic approach to health.

Caring for our mental wellbeing is just as important as maintaining our physical health.

It is estimated that 1 in 6 people living in Ireland and 1 in 4 people living in the UK will encounter a mental health problem each year ^1,2.

Recently there is much interest in the role that our diet can play in our mood and mental health.

Mental disorders, such as depression, are considered to be biochemically or emotionally based, but nutritional neuroscience is a developing area highlighting the association between nutritional influences and brain function^3..

Can the food we eat elevate mood or help us avoid feeling anxious or depressed? Let’s look at the evidence.

Dietary Patterns & Mental Health

Current evidence suggests that there is a link between diet and mental health. This research has investigated specific nutrients in isolation as well as dietary patterns.

Research examining dietary quality and dietary patterns suggests that a varied whole food diet, characterised by a selection of fruit and vegetables, unprocessed meat, fish and whole grains is associated with a lower risk for developing major depression, mild depression and anxiety disorders. This contrasts with findings that a ‘’western diet’’, characterised by a high intake of refined grains, processed or fried foods and high sugar options, is associated with an increased likelihood of developing depression and other detrimental psychological symptoms^4-5.

Recent research has shown that dietary intervention is very much worthwhile as a complementary therapy in the treatment of depression. 

For example, the SMILES Trial, which took place in 2017, included 56 individuals diagnosed with moderate to severe depression, some of whom were utilising psychotherapy or pharmacological support. Of these, 31 were treated with a dietary intervention and the other assigned to a social support group.

The dietary intervention included individualised nutritional advice and counselling led by a clinical dietitian. The advice encouraged the consumption of whole grains, vegetables, fruit, legumes, low fat dairy, dairy, fish, chicken and olive oil and emphasised reducing sweets, refined cereals, fast/fried food and sugary drinks.

The study concluded that dietary intervention group showed significantly greater improvements in depressive symptoms after 12 weeks when compared with the social support group⁶.

This goes to show that diet is not only important to support physical health but can be used as a tool to support overall health and wellbeing, indicating the possible need to move towards a more holistic and rounded approach to mental healthcare.

Summary: Evidence is emerging that a traditional Mediteraean-style diet may be a helpful complementary approach in the management of mental health issues such as depression. 

Individual Nutrients

It has also been suggested that a diet lacking nutrient dense whole foods may contribute to nutrient deficiencies. An adequate intake of folate, zinc, magnesium and other micronutrients may be protective against depressive and anxiety disorders. Such micronutrients are commonly found in a variety of vegetables and lean meat.

Let’s look at some of these individual nutrients and food components which are associated with having a positive impact on our mental health.

Antioxidants

There are a few reasons why healthy dietary patterns may improve mental health outcomes. One theory is that the high antioxidant content of fruit and vegetables may be protective against depression.

Antioxidants are substances that can balance levels of free radicals in the body. Therefore these can help to prevent or slow damage to our cells and promote better health.

The following nutrients and phytonutrients (plant chemicals) act as antioxidants in our body:

• Vitamin C: found in oranges, peppers, kiwis, lemons.
• Vitamin E: found in wholegrains, nuts, seeds, green leafy vegetables.
• Flavonoids: found in berries, oranges, legumes, tea, coffee.
• Lutein: found in spinach, kale, beetroot leaves, red peppers.
• Lycopene: found in tinned tomatoes, tomato puree, watermelon.

This indicates that eating in line with current recommendations of five or more portions of fruit and vegetables per day may be one factor which may reduce the risk of depression.

Folate & B-Vitamins

Folate, among other B vitamins, is essential for brain development and maintenance across the life cycle.

Furthermore, depressive symptoms can be observed with folate deficiency⁷.

Although the mechanism is not entirely understood, many studies of patients with neuropsychiatric symptoms have shown that those who are folate deficient, are also more likely to have low serotonin levels⁸. Serotonin is a neurotransmitter- commonly known as the ‘happy chemical’, associated with optimism and satisfaction and is actively involved in mood regulation⁹_.

Vitamins B1, B3 and B12 are necessary for obtaining energy from food and involved in the synthesis of many neurochemicals and signalling molecules. Insufficient intake can cause feelings of fatigue, depression and irritability¹⁴.

Examples of dietary sources:

• Folate: leafy green vegetables, fruit, legumes, fortified cereals.
• Vitamins B1, B3 & B12: wholegrains, meat, fish, eggs and dairy.

Important Minerals

Numerous studies have recognised that individuals who are depressed generally have reduced levels of zinc, when compared to those without depression.

Zinc is required for various processes within the body including DNA production and the synthesis of protein as well as being necessary for normal hormonal and immune and brain function.

Zinc works closely with a chemical known as brain derived neurotrophic factor (BDNF), a chemical in the brain promoting brain development, and so it is hypothesised that a deficiency may disrupt this relationship and possibly cause neuropsychiatric effects¹⁰.

Current evidence is suggestive of a relationship between magnesium depletion to depression and anxiety.

Magnesium is necessary for psycho-neuroendocrine systems and many biological pathways within the brain which are involved in the development of depression. It is also thought to influence the availability of certain corticosteroids to the brain.

Studies have found that exposure to anxiety, such as exam conditions, increases urinary magnesium output leading to a reduction of body magnesium levels. However, the current evidence is limited. Further research is warranted in this area, with a calling for some well-designed randomised controlled trials¹¹.

An adequate intake of iron protects against the development of iron deficiency anaemia (IDA), a condition affecting red blood cells ability to carry oxygen around the body.

IDA can cause tiredness and fatigue which can impair cognition and decrease productivity and academic performance. Some of those with IDA also show symptoms of anxiety and depression.

Iron plays a vital role in brain metabolism and is involved in the uptake and degradation of neurotransmitters and is incorporated into many transport proteins and enzymes^12,13.

Likewise, an association exists between levels of selenium in the diet and mood.

Those with lower selenium intake have reported increased feelings of anxiety, depression and fatigue^12,15.

Examples of dietary sources:

• Magnesium: almonds, bananas, broccoli, oatmeal, soybeans, wholegrains.
• Zinc: Oysters, lean beef, liver, egg yolk, bran.
• Iron: red meat, poultry and fish, beans & pulses, fortified cereals.
• Selenium: Brazil nuts, meat, fish, seeds, wholemeal bread.

Omega-3

Observational data indicates that a poor intake of oily fish (and dietary sources of omega 3) is associated with a higher incidence of depression.

Examples of oily fish include:

• Salmon
• Mackerel
• Herring
• Sardines
• Kippers
• Trout

Patients with diagnosed depression are reported to have a low cell content and low dietary intake of omega-3 fatty acids:  eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA).

It is proposed that EPA and DHA are necessary for the synthesis of neurotransmitters and other important chemicals which the brain needs to function efficiently¹⁶.

Consuming 1.5 – 2g of omega-3 supplements per day has been seen to elevate the mood of depressed patients.

However, it is important to consider that such supplements may not be suitable for everyone and it is advised to seek medical advice prior to commencing any supplement, especially if you take medication¹⁶.

For more information about omega-3 check out this post.

Choline

This nutrient plays an important role in brain function, nervous system function, mood and memory.

For example, choline is needed for the production of the neurotransmitter acetylcholine, which in involved in mood and memory.

Choline is also a component of cell membranes and is involved in cell signalling and early brain development.

Dietary sources of choline include:

• Beef
• Eggs
• Cod
• Chicken
• Milk and yoghurt
• Shitakke mushrooms
• Baked potato
• Kidney beans
• Baked beans
• Edamame beans

Summary: There are a number of nutrients which play an important role in mental health, such as: antioxidants, folate, B-vitamins, iron, zinc, magnesium, selenium, choline and omega-3 fats. 

Carbohydrates

Regular meals keep our brains working at its best by supplying a steady source of energy.

After consuming a meal containing carbohydrate, the level of glucose in our blood stream rises. This supplies energy to our organs, including the brain, allowing them to carry out physiological functions. 

After this glucose has been used up, or in periods of fasting, the blood glucose level drops, meaning that steady supply of ‘fuel’ is no longer as readily available.

When comparing cognitive performance in this, ‘fasted’ state versus after consumption of oral glucose, it is widely found that glucose administration improves brain power and memory performance in individuals^{17, 18}. 

One study found that there is an association between falling blood glucose levels and irritability also with aggression in frustrating situations.

The studies however cannot exclude the fact that this reaction could be due to several hormones and brain chemicals released in such a situation, but, perhaps the newly coined term ‘hangry’, does have some backing evidence! ¹⁷

Across the board however, few studies are available to show that stabilising blood glucose levels affects our mood significantly.

The limited available research suggests that higher blood glucose levels are associated with more positive moods, and lower blood glucose levels are associated with anxiety and nervousness.

This is especially relevant for those with type 2 diabetes, however in such individuals too much glucose in the blood is associated with anger and other characteristics of negative mood¹⁹.

In individuals without diabetes, our bodies do a good job of regulating the amount of glucose in our blood, using the hormone insulin. We can help our bodies with its blood glucose regulation, which may well enhance mood and cognition. 

Glycemic Index

Carbohydrate rich foods are absorbed and digested by the body in different ways meaning they raise the glucose levels at different rates. The glycaemic index (GI) of a food indicates whether it raises glucose concentration of the blood slowly (low GI), moderately (intermediate GI) or quickly (high GI).

The high-GI foods have a GI score greater than 70, intermediate-GI foods have a score greater than 55 and less than 70 and low-GI foods have a score below 55²⁰. These scores are calculated against the rate at which pure ingested glucose raises blood levels, which is given a score of 100 ²¹.

Essentially, as mentioned previously, we want a consistent steady source of fuel for a brain to function at its best. Low GI foods allow our blood glucose levels to rise and fall slowly, which avoids fast shifts upwards and downwards. Whereas high GI foods can cause sharp increases and drops in blood glucose.

That being said, it is important to note that not all low-GI foods are ‘healthier’ than high-GI foods. When considering the GI index of a food, it is also necessary to look at the other nutrients within the food. Crisps, chocolate and ice-cream often can have low to medium GI scores because of their high fat content, which slows their transit from their stomach to the gut and reduces the speed of absorption. A baked potato which generally has more vitamins, minerals and fibre, but less fat, is classified as a high GI food because if eaten in isolation is causes blood glucose to rise quickly ^21,22. Context matters. 

A study carried out in 2015 suggested that consuming more high GI foods was associated with an increased risk of depression²⁴.

It is possible that a high-GI diet, rich in refined carbohydrate (like: biscuits, white bread, sugar), may contribute to inflammation within the body, which has been associated with the development of depression.

It is also possible that consuming such foods can raise blood glucose quickly, leading to a sharp increase in blood glucose levels. To compensate for this our bodies produce lots of insulin which could lower our blood glucose again quickly, compromising brain glucose. This may trigger counter-regulatory hormone production such as cortisol, a stress hormone. If this repeats regularly it may cause down-regulation of glucose transport to the brain. All of these processes could potentially cause anxiety, irritability and mood disturbances²⁴.

However, in this study, those consuming higher GI diets also exercised less and were exposed to more stress than the group who consumed lower GI foods, so it is likely that these factors could also have influenced the prevalence of depression.

Claims that lower GI foods increase satiety are also common, however there is a paucity of evidence for this. More research is warranted around the effect of varying GIs on our physical and mental health.

Protein slows release of food from the stomach to the gut (gastric emptying) which slows down the rate of glucose absorption²¹. Carbohydrate rich foods which naturally contain protein, are found to cause increased post-meal insulin, which also assists in controlling steady blood glucose changes. This means that foods like, pasta and spaghetti generally have low GI scores due to the presence of the protein, gluten. Fats also help to slow gastric emptying.

Wholegrains like wholemeal bread, pasta and rice with higher fibre than their refined versions are beneficial when considering GI in the diet. The fibre is resistant to absorption and so slows down the rate at which food moves through our gut delaying intestinal absorption, having a GI lowering affect ^{22, 23} .

Balanced meals with a combination of healthy fats, protein and fibre with carbohydrates should lead to a stabilised blood glucose level and possibly enhance our moods.

Likewise, combining mixed beans and vegetables (protein and fibre containing) with a baked potato (high-GI) can slow down the rate at which you absorb the carbohydrates, leading to a more modest increase in blood glucose.

You can find a helpful GI search resource here: http://www.glycemicindex.com/ 

It is important to note that mental health issues can sometimes cause erratic eating patterns and ‘carbohydrate craving’. This can make it more difficult to regularly consume balanced meals.

Furthermore,  in many of the studies related to diet and mental health reverse causality cannot be completely ruled out. i.e. the mental health issue may be driving the eating behaviour, rather than the eating behaviour influencing the mental health outcome²⁵. 

Summary: Balanced meals which contain a combination of healthy fats, protein, fibre and low GI carbohydrates should help to stabilise blood glucose levels, as well as providing important nutrients to support mental health.

Conclusion:

Considering all the examined evidence, a varied wholefood diet could help to maintain mental well-being. 

Diet may be useful as a complementary therapy in the treatment of depression, alongside therapy and/or medication depending on each individual situation.

In particular, a varied whole food diet which provides enough omega-3 fatty acids and plenty of fruits and vegetables is associated with better mental health outcomes.

Eating regular balanced meals containing carbohydrate, protein and fat also helps to keep our brains powered and could help to stabilise mood. 

Click here to read Food & Mood – Part 2: Physiology

Click here to read Food & Mood – Part 3: Drinks

References:

1. Mind ‘’Mental Health Stats and Statistics’’ [Accessed September 2019 via: https://www.mind.org.uk/information-support/types-of-mental-health-problems/statistics-and-facts-about-mental-health/how-common-are-mental-health-problems/#.XZRrrUZKhyx]
2. Mental Health Ireland ‘Anxiety’ [Accessed October 2019 via  https://www.mentalhealthireland.ie/a-to-z/anxiety/]
3. Sathyanarayana Rao et al. (2008) ‘’Understanding nutrition, depression and mental illnesses’’ [Accessed October 2019 via https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2738337/]
4. Jacka et al. (2011). ‘’The Association Between Habitual Diet Quality and the Common Mental Disorders in Community-Dwelling Adults’’[Accessed September 2018 via https://insights.ovid.com/crossref?an=00006842-201107000-00009]
5. Jacka et al (2010) ‘’Association of Western and Traditional Diets With Depression and Anxiety in Women’’ [Accessed September 2018 via https://ajp.psychiatryonline.org/doi/full/10.1176/appi.ajp.2009.09060881?url_ver=Z39.88-2003&rfr_id=ori%3Arid%3Acrossref.org&rfr_dat=cr_pub%3Dpubmed&]
6. Jacka et al (2017) ‘’A randomised controlled trial of dietary improvement for adults with major depression (the ‘SMILES’ trial)’’ [Accessed September 2018 via https://bmcmedicine.biomedcentral.com/articles/10.1186/s12916-017-0791-y]
7. Sathyanarayana Roa et al (2008) ‘’Understanding nutrition, depression and mental illnesses’’ [Accessed October 2019 via https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2738337/]
8. McGarel et al  ‘’Emerging roles for folate and related B-vitamins in brain health across the lifecycle’’ (2014) [Accessed October 2019 via https://www.cambridge.org/core/journals/proceedings-of-the-nutrition-society/article/emerging-roles-for-folate-and-related-bvitamins-in-brain-health-across-the-lifecycle/4D024A2EEEE4126D725B74118DBEC2D3]
9. Dfarhud, Malmir & Khanahmadi (2014) ‘’Happiness & Health: The Biological Factors- Systematic Review Article’’ [Accessed October 2019 via https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4449495/]
10. Petrilli et al (2017) ‘’The Emerging Role for Zinc in Depression and Psychosis’’ [Accessed October 2019 via https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5492454/]
11. Boyle, Lawton & Dye ‘’The Effects of Magnesiu Supplementation on Subjective Anxiety and Stress- A Systematic Review’’ [Accessed October 2019 via https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5452159/]
12. British Dietetic Association (2017) ‘’Food and Mood’’ [Accessed October 2019, via https://www.bda.uk.com/foodfacts/foodmood.pdf]
13. Noorazar et al. (2015) ‘’Relationship between severity of depression symptoms and iron deficiency anaemia in women with major depressive disorder’’ [Accessed October 2019 via https://journals.tbzmed.ac.ir/JARCM/Manuscript/JARCM-3-219.pdf]
14. Kennedy (2016) ‘B Vitamins and the Brain: Mechanisms, Dose and Efficacy—A Review’ [Accessed October 2019 via ’https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4772032/]
15. Benton and Cook (1991) ‘The impact of selenium supplementation on mood’ [Accessed October 2019 via https://www.sciencedirect.com/science/article/abs/pii/000632239190251G]
16. Lakhan & Vieira (2008) ‘’Nutritional therapies for mental disorders’’ [Accessed September 2019 via https://link.springer.com/article/10.1186/1475-2891-7-2]
17. Benton (2002) Carbohydrate ingestion, blood glucose and mood’ [Accessed September 2019 via: https://www.sciencedirect.com/science/article/pii/S0149763402000040]
18. Sünram-Lea et al (2001) ‘Glucose facilitation of cognitive performance in healthy young adults: examination of the influence of fast-duration, time of day and pre-consumption plasma glucose levels’ [Accessed October 2019 via: https://link.springer.com/article/10.1007/s002130100771]
19. Rausch (2010) ‘Measures of Glycemic Variability and Links with Psychological Functioning’ [Accessed October 2019 via: https://link.springer.com/article/10.1007%2Fs11892-010-0152-0]
20. Diabetes UK ‘Glycaemic Index and Diabetes’ (2019) [Accessed October 2019 via https://www.diabetes.org.uk/guide-to-diabetes/enjoy-food/carbohydrates-and-diabetes/glycaemic-index-and-diabetes]
21. Eleazu (2016) ‘The concept of low glycemic index and glycemic load foods as panacea for type 2 diabetes mellitus; prospects, challenges and solutions’ [Accessed October 2019 via https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4994556/]
22. British Dietetic Association (2017) ‘Glycaemic Index’ [Accessed October 2019 via https://www.bda.uk.com/foodfacts/GIDiet.pdf]
23. Lattimer & Haub (2010) ‘Effects of Dietary Fibre and Its Components on Metabolic Health’ [Accessed October 2019 via https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3257631/]
24. Gangswisch et al (2015) ‘High glycemic index diet as a risk factor for depression: analyses from the Women’s Health Initiative [Accessed October 2019 via ’https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4515860/]
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