Review summary: Nutritional psychiatry and the gut microbiome

Author: Leanne Mitchell, APD

10 October 2020



Nutritional psychiatry is an emerging discipline that aims to use food and supplementation in the treatment or prevention of mental health disorders1.  Brain health and function relies on a steady supply of nutrients including lipids, amino acids, vitamins and minerals.  The availability of these nutrients is largely dependent on dietary adequacy, highlighting a plausible link between mental health and dietary intake.  Interest in this connection has produced growing research in the field of Nutritional Psychiatry.  Recently, a review on this topic was published, in which the evidence for the nutritional management of mental health disorders is provided2.  This practitioner update will provide an easy-to-digest summary of the review.


Article: Nutritional psychiatry: Towards improving mental health by what you eat2


Links between diet and brain or mental health


The review discussed research linking deficiency in B group vitamins with various brain-based symptoms or conditions (fatigue, memory loss or poor memory, depression, muscle weakness/paralysis, dementia).   The most important B vitamins for mental health and function are B12, B1 (thiamine), B9 (folic acid) and B2 (niacin). 

Special diets

The connection between nutrition and brain function is evident in diseases that require strict dietary management to reduce brain-based symptomology.  Examples cited in the review article include the ketogenic diet to reduce seizures in children with epilepsy and a low phenylalanine diet to reduce the risk of mental disorders, seizures and intellectual disability in people with phenylketonuria.  Additionally, the review discusses elimination diets (food additives and gluten-free, casein-free) as common interventions used by parents/guardians of children with ADHD or autism.  It is claimed that these interventions may help alleviate behavioural issues, however, the evidence of efficacy is limited, and findings usually rely on parental reports.

Early years

Early life nutrition is a key focus of nutritional psychiatry.  The review highlights human and animal research that indicates inadequate nutrition in early life negatively impacts cognitive function later in life.  Key nutrients required for brain growth include protein, iron, choline, folate, iodine, vitamins A, D, B6 and B12 and polyunsaturated fatty acids (particularly omega-3).

Later years

Many studies associate dietary patterns with mental health and cognitive function throughout the lifespan.  The review cites research which links unbalanced diets and high fat/high sugar western-style diets with cognitive impairment or decline.  Furthermore, western-style diets and obesity have been linked to issues with mood regulation, stress sensitivity and increased anxiety-like behaviour.  Conversely (and not surprisingly), higher diet quality, intake of antioxidant polyphenols and the Mediterranean diet have been associated with reduced risk of cognitive decline.


Strong correlational evidence supports the role of diet in depression and well-being.  The article cites a meta-analysis of 16 randomised controlled trials that concludes dietary management is a promising treatment to reduce the symptoms of depression.  The review notes multiple individual studies that found higher intake fruit and/or vegetable was associated with increased feelings of well-being and happiness.  Also referenced in the review article are several meta-analyses and systematic reviews that compile observational evidence linking a Mediterranean diet or a “healthy diet” with a reduced risk of depression.  Conversely, one meta-analysis failed to find an association between adherence to a Mediterranean diet and the risk of depression for the cohort studies included in the analysis.  However, analysis of the cross-sectional studies found that increased adherence to a Mediterranean diet was protective against depression.


The role of the gut microbiome

Diet is a key influencer of microbial composition and function in adults3,4.  So, if diet is connected to mental and brain health, it is not surprising that the gut microbiome may be involved in this relationship. The review highlights research that indicates infancy is a critical period where the gut microbiome plays an important role in brain development and is linked to the risk of developing mental disorders later in life. Preclinical studies may provide an explanation for this connection, with findings demonstrating the infant gut microbiome plays a role in training the stress response and immune systems5,6.  In infancy and beyond, stress has been shown to disrupt digestive function and microbial composition7

Moreover, the gut microbiome plays a role in the metabolism of serotonin, a neurotransmitter involved in mood and wellbeing.  The review goes on to highlight a clinical trial in which a prebiotic (fibre) supplement reduced age-related microglial activation (a mediator of neuroinflammation) in elderly participants. 

Finally, the article notes that high-fibre and Mediterranean dietary patterns are linked to microbial diversity and that these dietary patterns are also associated with a reduced risk of depression (as discussed above). These findings point to the importance of diet in shaping the gut microbiome which may, in turn, mediate gut-brain interactions that support mental health.


Key considerations

  • The evidence used in the field of nutritional psychiatry is based primarily on associative (correlational) relationships.
  • Investigating causality, and the underlying mechanisms involved in gut-brain interactions is an important next step for research.
  • Dietary patterns may be more important to consider than individual nutrients due to possible co-operative functions between nutrients.
  • Nutritional advice should always be personalised to maximise success. A “one size fits all” approach fails to take into account individual differences such as genetics, comorbid conditions and other lifestyle factors.


Practical implications

To support clients with mental health disorders, practitioners should consider the following:

  • Optimise gut health. The Microba Insight Report aids practitioners in their clinical decision making. The results allow practitioners to work with their clients to maximise the health-promoting capacity of their gut microbiome.  These improvements may help support mental health.
  • Encourage clients to follow a balanced diet. Eating a balanced diet will help ensure adequate intake of nutrients required to support brain and mental health.
  • Educate or refer clients at risk of deficiencies to a qualified professional to receive personalised nutritional advice to help achieve adequacy. Client’s at risk could include those following a vegan, vegetarian or low grain/carbohydrate dietary patterns or those needing to restrict their diet due to food allergies or intolerances.
  • Encourage increased prebiotic fibre intake.
  • Suggest adopting some Mediterranean eating practices such as increasing fruit, vegetable and omega-3 (seafood, nuts/seeds and plant oils) intake.
  • Encourage clients to find time for stress management. This will be different from client to client – running, boxing, yoga, meditation, music – whatever best suits them and their lifestyle.


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About the Author


Leanne Mitchell

Leanne is an Accredited Practising Dietitian and works as one of the microbiome coaches at Microba. Leanne has a developing interest in the clinical application of the gut-brain axis in gastrointestinal disorders, mental health and neuro-developmental conditions.


(1) Sarris J, Logan AC, Akbaraly TN, et al. International Society for Nutritional Psychiatry Research consensus position statement: nutritional medicine in modern psychiatry. World Psychiatry. 2015;14(3):370-371. doi:10.1002/wps.20223

(2) Adan RAH, van der Beek EM, Buitelaar JK, Cryan JF, Hebebrand J, Higgs S, et al. Nutritional psychiatry: Towards improving mental health by what you eat. Eur Neuropsychopharmacol. 2019;29(12):1321-32.

(3) David, L., Maurice, C., Carmody, R. et al. Diet rapidly and reproducibly alters the human gut microbiome. Nature 505, 559–563 (2014).

(4) Xu, Z., & Knight, R. (2015). Dietary effects on human gut microbiome diversity. British Journal of Nutrition, 113(S1), S1-S5. doi:10.1017/S0007114514004127

(5) Sudo, N., Y. Chida, and C. Kubo, Postnatal microbial colonization programs the hypothalamic-pituitary-adrenal system for stress response in mice. J. Psychosomat. Res., 2005. 58(6): p. S60-S60.

(6) Codagnone MG, Spichak S, O’Mahony SM, O’Leary OF, Clarke G, Stanton C, et al. Programming Bugs: Microbiota and the Developmental Origins of Brain Health and Disease. Biol Psychiatry. 2019;85(2):150-63.

(7) Dinan TG, Cryan JF. Regulation of the stress response by the gut microbiota: Implications for psychoneuroendocrinology. Psychoneuroendocrinology. 2012;37(9):1369-78.