The link between diet and depression

The issues of mental health are very rarely out of the news and either directly, or indirectly, affect the vast majority of us at some point in our lifetime – whether that be through personal suffering or that of a close friend or family member. Indeed, it is considered that as many as 1 in 4 people suffer with a mental health illness each year.

We are all aware of the pressures of today’s lifestyle, with increased use of social media, financial pressure, work stress and political uncertainty. However, it has now become increasingly clear that your diet can have a huge impact of your mental health. Although diet cannot change those external influences, it can affect how your body copes with them as well as affecting the production of hormones and neurotransmitters which play vital roles in the regulation of mood.

This week’s blog aims to outline dietary changes that can affect mood and help overcome symptoms of depression.


Our biochemistry can have a big impact on mood, in fact this is how many anti-depressants work. The neurotransmitter serotonin is involved in balancing mood, anxiety and happiness and low levels have been associated with depression. Most anti-depressant drugs aim to increase serotonin in the brain (or reduce the breakdown of it), but we can increase our serotonin levels more naturally avoiding side effects associated with anti-depressant use.

Serotonin is produced from tryptophan which is an amino acid and therefore found in protein rich foods (however foods specifically high in tryptophan include; fish, walnuts, oats, pumpkin seeds, legumes and bananas).

Tryptophan is converted into 5-hydroxytryptophan (5HTP) in the presence of cofactors; iron, B3 and folate. 5HTP then requires magnesium and B6 to be converted into serotonin, it is possible to take 5HTP as a supplement (5HTP can cross the blood brain carrier whereas serotonin cannot) however it should always be taken in conjunction with magnesium and B6 to ensure adequate conversion.

It has been shown that serotonin production increases with exposure to daylight as well as with exercise, therefore it is really important to ensure that you get some time outside, for example a midday brisk walk would be ideal. Incidentally at night the pineal gland within the brain then recognises that light levels have dropped and begins converting serotonin into melatonin, our sleep neurotransmitter, this is one of the reasons why many people who suffer with depression may have problems sleeping.

The role of the gut

Interestingly approximately 90% of serotonin is produced in the digestive system, although this cannot cross the blood brain barrier it does have many functions relating to gut health. Serotonin produced in the gut binds to receptors which stimulate the vagus nerve (the nerve that runs from the gut to the Central Nervous System, CNS) and is part of our enteric nervous system. Natural stimulation of the vagus nerve in the gut can influence the brain and effect mood. When there is normal stimulation mood can be improved, however, when stimulation is abnormal due to dysfunction within the digestive system, mood can be disturbed.

Gut microflora have a strong influence on the production of serotonin within the gut and therefore on the stimulation of the vagus nerve. Research suggests that commensal bacteria within the gut stimulate the host intestinal cells to produce serotonin. Therefore, supporting the balance of microflora within the gut is also important for both serotonin production and the maintenance of stable mood.

As with so many conditions the integrity of the digestive lining also plays a significant role. When the digestive lining is compromised by inflammation, oxidative stress and damage, larger molecules can pass through into the blood stream, triggering systemic inflammation, this is known as leaky gut (click here to read our blog on leaky gut syndrome).

Research has shown that when the integrity of the gut lining is compromised so is the integrity of the blood brain barrier. Therefore, molecules which should be kept out of the brain can cross into it and trigger neuro-inflammation; it is known that this can affect mood and depression and also have a significant effect on cognitive function.

Incidentally 50-90% of patients with IBS also experience anxiety, depression or other psychiatric disorders. Therefore, the health of the gut always should be considered for anyone who is experiencing depression.

Consider supporting a healthy bowel flora by:

  •  Consuming fermented foods such as kefir, kombucha, sauerkraut and miso
  • Consuming prebiotic (fuel for gut bacteria) foods and polyphenols from chicory, olives, baked apples and Jerusalem artichoke.
  • Take a live bacteria supplement

Nutrients that research has shown are important for repair and integrity of the digestive lining include:

  • Vitamin A
  • Vitamin D3
  • L-Glutamine
  • Zinc

Inflammation and oxidative stress

As mentioned earlier inflammation within the brain can affect cognitive function as well as mood. Increased activation of the immune cells within the CNS, known as microglia, has been demonstrated in patients with depression. As well as generating inflammatory cytokines, microglia play a role in managing neuronal cell death, neurogenesis, and synaptic interactions. They also secrete glutamate and metabolise kynurenine to quinolonic acid, both of which are neurotoxic and can result in damage or death to neural cells. This highlights the importance of supporting the health of the blood brain barrier and also of reducing inflammation.

When we have inflammation we also see higher levels of oxidative stress. Oxidative stress causes damage to mitochondria and therefore contributes to mitochondrial dysfunction. This leads to impaired energy production within the cell or apoptosis (cell death) which can affect overall neuronal function and is again a risk factor for depression.

Therefore, reducing inflammation and oxidative stress should be considered. Reduce inflammation by:

  • Optimising gut health
  • Reducing omega 6 fatty acids from meat, dairy and vegetable oils
  • Increasing omega 3 fatty acids from oily fish, chia and flax seeds and dark leafy green vegetables
  • Using anti-inflammatory foods such as turmeric (curcumin) and ginger
  •  Increasing vitamin E containing foods such as avocado

Reduce oxidative stress by:

  • Removing exposure to pro-oxidative toxins such as heavy metals, pesticides and persistent organic pollutants
  • Increasing anti-oxidants such as vitamin A, vitamin C, CoQ10, selenium, zinc, N-acetyl-cysteine and alpha-lipoic acid. Vitamin C and NAC will also support the synthesis of glutathione, an antioxidant made in the body. Glutathione can also be supplemented directly

Blood Sugar Control

Poor regulation of blood sugar and insulin resistance can lead to low mood as well as adrenal dysfunction which is also a contributor to depression. Therefore, it is essential to ensure blood sugar levels are well regulated when considering mood disorders.

Blood sugar regulation can be improved by including healthy fats and protein with each meal in order to slow down the release of sugar into the blood stream. It can also be useful to ensure there are adequate levels of nutrients involved in blood sugar regulation such as chromium, magnesium, zinc and alpha lipoic acid.

Time restricted feeding, where you fast for at least 12 hours in a 24 hour period, has also been shown to reduce insulin levels which can improve insulin sensitivity (click here to read our blog on Time Restricted Feeding).

Low levels of some nutrients have been associated with depression

B Vitamins

As previously mentioned B6 is important for the production of serotonin, however folate and B12 play a further role when it comes to mood.

SAMe is a major methyl donor, along with L-methylfolate and methylcobalamin (B12), and methylfolate increases levels of SAMe. All of these are involved in the methylation of tetrahydrobiopterin (BH4). BH4 is a coenzyme and is essential for activating enzymes that manufacture serotonin and dopamine, both of which are important for mood.

Methylfolate, B12 and SAMe all stimulate BH4 production. Deficiencies of folate and B12 have been associated with depression, and the reason for this is at least partly thought to be due to the activation of BH4.

Essential Fatty Acids

The anti-inflammatory effects of essential fats, specifically EPA, are well recognised and therefore play a beneficial role in mood by supporting anti-inflammatory pathways. The essential fat DHA also plays an important role in mood and cognition. DHA is the predominant omega 3 fatty acid found in the brain and deficiencies are associated with low mood. Phospholipids are also important as they are incorporated into cells membranes and aid cell fluidity and signalling, both of which can be impaired in depressed patients.


Zinc a cofactor for more than 70 metalloenzymes, low zinc levels have been associated with depression.

Vitamin D

Vitamin D deficiency has been attributed to low mood associated with seasonal affective disorder. It has been suggested that vitamin D influences nerve growth factors, acetylcholine, serotonin, testosterone and thyroid hormone all of which have relevance to the pathogenesis of depression.

General interventions

So if you want to improve mood, consider:

  • Foods which contain tryptophan e.g. walnuts, turkey, oats, bananas
  • B6 and magnesium which convert 5HTP to serotonin
  • Gut health, suspect leaky gut and / or dysbiosis
  •  Inflammation consider an anti-inflammatory diet as well as anti-inflammatory nutrients such as Omega 3 fats (as EPA), turmeric and ginger
  • Support anti-oxidant status and reduce oxidative stress
  • Is there a need for additional vitamin D, zinc and methylation support (eg methylfolate and methylcobalamin)

If you have any questions regarding the health topics that have been raised please don’t hesitate to get in touch with Clare via phone; 01684 310099 or e-mail

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