Food & Mood: Exploring the Science Behind Nutrition’s Role in Mental Wellness

We all have our good days and bad days for mood. This is relevant now more than ever. The COVID-19 pandemic has caused many people all over the world to feel increasing levels of anxiety, uncertainty and isolation.

People are adjusting to working from home, which makes it even more difficult to strike a work-life balance. Many are feeling isolated from family and friends. Our emotional and mental health are as important as our physical health and together with regular exercise, sleep and social interaction, evidence suggests that the foods we eat may also impact the way we feel.

The link between food and mood will come as no surprise. There is joy and social connection when sharing birthday cake with loved ones. Certain tastes and smells evoke feelings of nostalgia from childhood. On the other hand, it is common to feel irritable during long periods of fasting, and feelings of guilt are common when overeating. The commonly used terms ‘comfort’ food and ‘hangry’ define how food can bring an emotional response.

Scientific research in the area of food and mood is ever advancing. Many nutrients and dietary patterns have been linked with our neurological state. Let’s explore the latest evidence.

The content of this article is intended for informational use only. It is not intended to be used for treatment or management of any disease, or for claim guidance.

Vitamins, minerals, and mood

Micronutrients are required for the synthesis of many chemical messengers in the brain known as neurotransmitters. Serotonin, dopamine, γ-aminobutyric acid (GABA), and noradrenaline are the 4 major neurotransmitters that regulate mood, which is why these are commonly known as ‘happy hormones’.  These chemical messengers are necessary to balance the intensity of signals between neurons in the brain and rest of the body. Low levels of serotonin in particular have been linked with neurological disorders, anxiety and depression (1).

B vitamins are essential cofactors for the synthesis of neurotransmitters. Choline is a unique nutrient because it is not classified as a vitamin or a mineral. However, it is required for the production of neurotransmitter acetylcholine, which is involved in mood and memory.  Some evidence shows that folate, zinc, magnesium, iron, selenium and vitamin D may be protective against anxiety, mood swings, and irritability. Numerous studies have shown that patients diagnosed with depression are often deficient in one or more of these micronutrients (2).

A well-balanced diet will provide adequate sources of these nutrients, as they are commonly found in a variety of foods.

Dietary sources:

• Folate: Green leafy vegetables, beans, peas, lentils, fortified foods and beverages.
• Zinc: Red meat, liver, egg yolk, oysters, bran.
• Magnesium: Almonds, bananas, broccoli, oatmeal, soybeans, whole grains.
• Iron: Red meat, poultry and fish, beans & pulses, fortified cereals.
• Selenium: Brazil nuts, meat, fish, seeds, wholemeal bread.
• Vitamin D: Sunlight, fortified foods and beverages, eggs.
• B vitamins: Whole grains, meat, dairy, eggs, seeds, nuts, legumes, fruits and vegetables.
• Choline: Beef, eggs, fish, chicken, dairy, shiitake mushrooms, beans.

Energy and mood: Carbohydrates, Glycemic Index (GI) and fueling the brain

The brain requires glucose as its main source of fuel. In fact, the brain uses 20% of the glucose needed by the body, which means we require carbohydrate throughout the day for our brain to function at its best. The Glycemic Index of a food refers to the rate at which carbohydrates (glucose) are released into the blood. High GI foods, such as processed foods, sugar-sweetened beverages, confectionery and cakes can cause dramatic spikes and drops in blood glucose. This fluctuation in blood glucose is often referred to as the ‘sugar crash’ and is associated with irritability, lack of concentration, feeling weak and mood swings. Sharp peaks in blood glucose can also trigger the stress hormone cortisol. One study suggests that consuming more high GI foods is associated with an increased risk of depression (3).

It is recommended to choose low GI foods because they allow our blood glucose levels to rise and fall slowly. These foods are typically high fibre whole grains, oats, fruits and vegetables. Furthermore, eating regular, well-balanced meals with a combination of carbohydrate, protein and healthy fats provides stable blood glucose levels throughout the day as fat and protein can slow the rate of carbohydrate absorption. For example, combining a baked potato (high GI) with mixed beans (protein & fibre) could help to prevent any sudden crashes in glucose for the brain and subsequent mood disturbances (4).

There is an additional ‘mood-enhancing’ benefit to consuming carbohydrates alongside proteins. Carbohydrates can increase the availability of amino acid tryptophan to the brain (5). Tryptophan is a precursor for the production of serotonin, the ‘happy hormone’. Sources of tryptophan include eggs, poultry, dairy and tofu. This may explain why individuals crave ‘comfort’ carbohydrates during times of stress.

Omega-3 fatty acids and brain health

Approximately 60% of the brain is made up of fatty acids, which include omega-3 fats. As a result, omega-3 fats are essential for the normal function of the brain. Sources of omega-3 include oily fish, seeds like chia, flax, and hemp, nuts, fortified foods and supplements. Epidemiological studies show that in countries where people eat large amounts of oily fish, depression is less common (6).

In addition, omega-3 fats have anti-inflammatory effects on the body by releasing chemicals called eicosanoids. Many neurological conditions such as depression and Alzheimer’s Disease are associated with increased inflammation in the brain. Therefore omega-3 fats have the potential to reduce the inflammation associated with these conditions, and in doing so may relieve some of the neurological symptoms.

More than 30 clinical trials have investigated omega-3 supplementation in people with depression (7). Current evidence supports that omega-3 consumption of ~1 g/d (containing at least 60% eicosapentanoic acid EPA) can elevate the mood of patients diagnosed with depression (8). This is similar to eating 3 salmon fillets per week.

Hydration’s role in energy and mood

Adequate hydration is often considered to impact cognition and concentration. The body is ~75% water and is fundamental to all biological functions and metabolic pathways. Therefore, it is imperative that we stay adequately hydrated to maintain physical and mental health. Even mild dehydration can impact mood and alertness (9).  It has also been observed that memory, motor skills and numeric abilities decline in states of moderate dehydration. However, these findings have not been consistent. Our thirst sensation kicks in once already dehydrated by 1-2%, which means our body is already reducing performance. Heat stress can be experienced by those living in hot climates, those carrying out heavy labour during hot seasons or those performing exercise. It can affect mood and increase feelings of distress. It is recommended to drink at least 2 litres of fluid per day.

Both caffeine and alcohol are commonly used for enhancing mood at low to moderate intakes. However, withdrawal from these substances can cause irritability, headache, fatigue and poor concentration (10, 11). Alcohol is classified as a depressant and excessive consumption is highly correlated with mental health disorders. Excessive alcohol consumption is also associated with B vitamin deficiencies which can further lead to anxiety and depressive symptoms as mentioned earlier (11).

The Mediterranean Diet and Depression

Evidence is emerging that a Mediterranean-style diet promotes brain and mental health and may be helpful in the management of conditions such as depression (12). A Mediterranean diet consists of whole grains, fruits, vegetables, dairy, fish, lean meats and olive oil and is considered one of the most healthful dietary patterns in the world. It is a diet rich in anti-oxidants, polyphenols, micronutrients, fibre and healthy fats. The aptly named ‘SMILES trial (Supporting the Modification of Lifestyle in Lowered Emotional States)’ was a pioneering randomized control trial investigating the effects of this diet on outcomes of depression (13).

The results of the study, published in the international journal BMC Medicine, showed that participants who followed a Mediterranean diet for 12 weeks had a much greater reduction in their depressive symptoms over the three-month period, compared to those in a control group who received ‘befriending’ social support. At the end of the trial, a third of those in the dietary intervention group met criteria for remission of major depression, compared to 8% of those in the social support group. These results were not explained by changes in physical activity or body weight, but were closely related to the extent of dietary change. In other words, those who improved their diet the most experienced the greatest benefit to their depression. It is likely that the benefits are a results of the dietary pattern as a whole, rather than individual foods or nutrients. More research needs to be carried out to untangle the mechanism linking the Mediterranean diet to improved mental health.

The Gut-Brain connection

Have you ever experienced a ‘gut feeling’ or ‘butterflies’ in your stomach? Anger, nerves, sadness, love, or excitement can all trigger symptoms in the gut. The connection goes both ways; intestinal distress can be the cause of anxiety or depression. The link between gut health and mental health has been known for centuries. However, an explosion of research in the past decade has begun to unravel the science behind this intimate connection.

The gut microbiome is an eco-system of trillions of species micro-organisms living inside the gastrointestinal tract. These bacteria play a vital role in our health, digesting the food we eat, protecting us from infection and producing chemicals such as short chain fatty acids and neurotransmitters. Often referred to as the second brain our gut contains millions of neurons which communicate with the brain. A dysfunctional gut microbiome is linked with anxiety, depression among other neurological conditions.

Much of the research into the brain-gut-microbiota axis has been carried out in animals by studying antibiotics, probiotics and fecal transplants to determine their effects of the gut microbiota on brain activity. Animal studies have consistently shown that gut bacteria signal to the nervous system, influencing behaviour and stress responses (14).

Human studies are emerging, and there is preliminary evidence that diet and probiotic supplementation may improve symptoms in many neurological conditions (15). Psychobiotics are a newly coined term which refer to probiotics which, when consumed in adequate amounts, may have positive effects on mental health (16). A pilot study in 2017 was the first to show that probiotic supplementation can improve depressive symptoms in patients with Irritable Bowel Syndrome (17). Another study found that healthy individuals showed reduced patterns of negative and aggressive thoughts when given a multispecies probiotic over 1 month period (18). Further studies are needed since research remains at the early stages. However, it is promising that targeting the microbiome could assist in the treatment of a wide range of disorders in the future, including anxiety and depression.

At present, the best way to support your gut microbiome is to consume a varied balanced diet consisting of lots of plants, fruits, vegetables and legumes. These foods contain prebiotics, fibre, and polyphenols, which feed and diversify our gut microbiota. Fermented foods such as yoghurt, kefir, kimchi and kombucha can also support your gut microbiome.

What are Nootropics?

A new wave of products claiming to boost brain function are hitting the mainstream market. These are collectively known as Nootropics, which comes from the Greek work ‘mind’ (noos) and ‘turning’ (tropic). Nootropics have been positioned to improve memory, attention span, relaxation and energy. Caffeine and B vitamins are considered nootropics and are often used in energy stimulant beverages.

However trending nootropic ingredients include:

• Cannabidol (CBD) has been suggested to relieve anxiety, as the non-psychoactive cousin of tertrahydrocannabinol (THC). This can be found in the hemp plant.
• GABA (gamma amino butyric acid) is the brain’s inhibitory neurotransmitter. Its role is to slow down neuron circuits and restore balance. It is claimed to improve focus and relaxation.
• L-theanine is a compound found in green tea. It is claimed that L-theanine can cross the blood-brain barrier rapidly to increase GABA production in the brain and in turn improve focus and relaxation.
• Gingko biloba is a tree native to China which is often associated with claims to have anti-oxidant and anti-inflammatory effects on the brain, improving brain function and reducing anxiety and stress.
• Panax ginseng is a native Korean plant which claims to improve concentration and memory.

Caution is needed when interpreting the marketing claims many of these products carry as there is a significant lack of consistent randomized control trials to support these ‘claims’.

Food for thought

While we still have much to learn about the effects of our diet on mood and mental health issues, evidence suggests that a healthy diet can have a protective effect. Nourish your body and your mind with well balanced meals at regular intervals throughout the day. Diet in combination with physical exercise, adequate sleep and social connection (even if it needs to be at a distance for now), will support a healthy and happy mind.

• References
  1. Berger, M., Gray, J. and Roth, B., 2009. The Expanded Biology of Serotonin. Annual Review of Medicine, 60(1), pp.355-366.
  2. McGarel et al  ‘’Emerging roles for folate and related B-vitamins in brain health across the lifecycle’’ (2014)
  3. Gangswisch et al (2015) ‘High glycemic index diet as a risk factor for depression: analyses from the Women’s Health Initiative
  4. Benton (2002) Carbohydrate ingestion, blood glucose and mood’ Neurosci Biobehav Rev. 26(3):293-308
  5. Wurtman, RJ., Wurtman, JJ., Regan, MM., McDermott, JM., Tsay, RH. and Breu, JJ. (2003). Effects of normal meals rich in carbohydrate or protein on plasma tryptophan and tyrosine ratios. American Journal of Clinical Nutrition 77 (1) pp.128-32
  6. Larrieu, T. and Layé, S., 2018. Food for Mood: Relevance of Nutritional Omega-3 Fatty Acids for Depression and Anxiety. Frontiers in Physiology, 9.
  7. Liao, Y., Xie, B., Zhang, H. et al. Efficacy of omega-3 PUFAs in depression: A meta-analysis. Transl Psychiatry 9, 190 (2019). https://doi.org/10.1038/s41398-019-0515-5
  8. Adams, P., Lawson, S., Sanigorski, A. and Sinclair, A., 1996. Arachidonic acid to eicosapentaenoic acid ratio in blood correlates positively with clinical symptoms of depression. Lipids, 31(1), pp.S157-S161.
  9. Benton, D., 2011. Dehydration Influences Mood and Cognition: A Plausible Hypothesis?. Nutrients, 3(5), pp.555-573.
  10. Ruxton, C., 2008. The impact of caffeine on mood, cognitive function, performance and hydration: a review of benefits and risks. Nutrition Bulletin, 33(1), pp.15-25.
  11. Sullivan, L., Fiellin, D. and O’Connor, P., 2005. The prevalence and impact of alcohol problems in major depression: A systematic review. The American Journal of Medicine, 118(4), pp.330-341.
  12. Sánchez-Villegas, A., Henríquez, P., Bes-Rastrollo, M., & Doreste, J. (2006). Mediterranean diet and depression. Public Health Nutrition, 9(8A), 1104-1109. doi:10.1017/S1368980007668578
  13. Jacka FN et al. A randomised controlled trial of dietary improvement for adults with major depression (the ‘SMILES’ trial). BMC Med. 2017;15:23.
  14. Dinan & Cryan (2017) ‘Brain-Gut-Microbiota Axis and Mental Health’
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