The impact of nutrition on depression

19th Oct 2023

Depression:

Major depressive disorder (MDD) is the most predominant illness amongst mental, neurological and substance abuse disorders⁽¹⁾, with a lifetime prevalence of at least 10% and the risk in women twice that in men⁽²⁾ . Research suggests that MDD is the most pervasive comorbid disorder to co-occur with generalised anxiety disorder (GAD), with a lifetime comorbidity rate of 90%⁽³⁾.

Naturopathic and functional medicine explanation

Unravelling the multifactorial root causes of depression is challenging and looking at a broad amalgamation of unique factors such as vitamin D levels⁽⁴⁾, gut microbiome diversity (5) amino acids and minerals⁽⁶⁾, toxin exposure⁽⁷⁾, mitochondrial dysfunction⁽⁸⁾, inflammation⁽⁹⁾, omega-3 polyunsaturated fatty acids (n-3FA)⁽¹⁰⁾, diet⁽¹¹⁾  and lifestyle factors alongside adrenal function, thyroid health⁽¹²⁾, neurotransmitter signalling⁽¹³⁾  and blood sugar balance⁽¹⁴⁾  allows functional medicine to create a unique insight into depression.

Gut microbiome:

A bidirectional relationship between the gut and the brain, connected via the microbiota-gut-brain axis involves communication via endocrine, neural and immune pathways⁽¹⁵⁾, to mediate key processes including neurotransmission, neuroinflammation, neurogenesis and activation of the hypothalamic-pituitary-adrenal (HPA) axis^{(16) .} Researchers indicate via MRI, the gut microbiome composition is correlated with neural activity and brain structure⁽¹⁷⁾. The gut microbiota profiles of those with depression have shown a narrowing microbial diversity⁽¹⁶⁾.

Vitamin D:

A wealth of research indicates lower vitamin D levels are associated with both minor and major depression alongside depressive symptoms in a range of ages from 18⁽¹⁸⁾ to the elderly population, finding those with severe vitamin D deficiency were twice as likely to have depression⁽¹⁹⁾ .  Vitamin D has shown to have a neuroprotective role in the brain⁽²⁰⁾ and modulates the HPA axis, regulating the synthesis of dopamine, adrenaline and noradrenalin through vitamin D receptors in the adrenal cortex⁽²¹⁾, leading to alterations in mood. Furthermore, vitamin D has shown to protect against dopamine and serotonin centrally⁽²²⁾.

Diet:

Fibre from fruit, vegetables, legumes and wholegrains have shown to be beneficial to those with depression, modulating the gut microbiome⁽²³⁾ and promoting immune functioning⁽²⁴⁾. Furthermore, phytochemicals found in wholegrains are protective against oxidative stress, which may be a result of inflammation found in those with depression⁽²⁵⁾. Refined sugary, high fat diets which lack dietary fibre not only impact the gut microbiome and immune function but also reduces Brain derived neurotrophic factor (BDNF), neuronal plasticity and learning within the hippocampus, which has been linked to depression⁽²⁶⁾.

A wealth of evidence supports the traditional Mediterranean diet (TMD) as a treatment for depression, characterized by low intakes of red meat, processed foods and confectionaries; with focus on a high intake of plant foods (legumes, fruit, vegetables, nuts , seeds, wholegrains, olives) a moderate intake of fish and extra virgin olive oil as the main intake of fat⁽²⁷⁾.  In addition, research provides compelling support for the use of a TMD alongside fish oil supplementation of 900mg DHA and 200mg EPA for 3 months, for treating depression⁽²⁸⁾. A 45% improvement in depression scores were reported in those who had a dietary intervention, in contrast to 26.8% in the control group.

A TMD is rich in polyphenols and fibre, supporting the gut microbiome diversity, reducing dysbiosis, thus supporting the immune function and reducing the activation of the inflammatory cascade⁽²⁹⁾ , which has shown to be linked to depression. Adherence to a TMD ensures adequate B vitamin intake, imperative for several methylation reactions, including neurotransmitter production⁽³⁰⁾.

Final thoughts:

• In terms of practical application, promoting a TMD is the most important change that should be recommended. Incorporating a high intake of plant foods (legumes, fruit, vegetables, nuts , seeds, wholegrains, olives) a moderate intake of fish, extra virgin olive oil and reducing red meat, processed foods and confectionaries is advisable. This in turn will support the gut microbiome, reduce inflammation and provide an abundance of micronutrients, supporting cognitive function and reducing depressive symptoms⁽²⁹⁾. Improving the diet increases essential nutrients which work synergistically in contrast to single nutrients.
• It is warranted to incorporate 7 portions of different-coloured vegetables rich in fibre, nutrients and antioxidants, to increase microbial diversity⁽³¹⁾ resulting in a supported immune system⁽³²⁾.
• Probiotic foods (sauerkraut, miso, kimchi, kefir) should ideally be consumed daily, to support the gut microbiome⁽³³⁾.

Author: Hannah Frais

Nutritional therapist BSc (Hons), DipCNM, mBANT, mANP

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