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The condition

Mental health refers to a person’s ability to cope with the normal stresses of life and engage in enjoyable or helpful tasks within their family, workplace and greater community. Mental illness may be considered when these areas are compromised; however it requires a holistic assessment of the person to consider changes in their thoughts and feelings, physical health, behaviours, life events, work and social functioning as well as their family’s concerns, capacity and cultural and religious norms.

Conditions such as anxiety and depression are considered when thinking, feelings and/or functioning are greatly impacted in particular or broad areas of a person’s life over a specific period of time. Depression and anxiety disorders are the most prevalent psychiatric conditions in Australia and New Zealand. 15% of Australian adults aged 16 to 85 have experienced a depressive illness and over 26% have experienced an anxiety disorder, and very similar figures obtain in New Zealand.

The cause

Many aspects of mental health are out of our control such as experiencing a traumatic event, but there are also many that we can optimise. Good nutrition, sleep, relaxation, exercise and connection with others are key in supporting good mental health. A Western diet, high in fats, refined flours, sugar and highly processed foods is associated with an increased risk of a depressive illness. A prospective study of 43,685 women over an average of 12 years, as part of the Nurse’s Health Study in the USA, found that women with no mental illness at the commencement of the study who consumed a diet high in red meat, fish, soda and refined grains were 41% more likely to develop depression than those in the group with the lowest intake of these foods [1].

The nutrition prescription

Consuming a plant-based diet can promote mental wellbeing in many ways. Our bodies function best on a nutrient-rich, high fibre diet, abundant in fruits, vegetables, wholegrains, legumes and some nuts and seeds. The gut-brain connection is profound and continues to be explored in research. So far we know of several ways the gut can influence mental health. The gastrointestinal tract is responsible for producing important neurotransmitters used by the brain to help regulate mood, such as serotonin and acetylcholine. It also connects via neurons, including the vagus nerve, and through the functions of the gut microbiome, which includes the balance of bacteria and production of inflammatory markers in the intestines.

  • A 2015 interventional study involving 292 employees of a large insurance company in the USA found significant improvement in impairment from depression, anxiety and fatigue following an 18 week dietary intervention where participants received weekly instruction on implementing a healthy vegan diet [2].
  • Excluding animal products can reduce many inflammatory markers that affect the gastrointestinal tract such as arachidonic acid and monoamine oxidase (MAO) [3], and C-reactive protein (CRP) [4].
  • Plant foods contain antioxidants, such as vitamin C, which help to reduce oxidative stress. High levels of oxidative stress may increase the risk of developing depression [5].

Vitamin B12 supplementation is essential for all people who are on a plant-exclusive diet. A vitamin B12 deficiency can cause severe harm to the nervous system and increase the risk of developing depression [6].

Medical supervision of diet change is essential

Shifting to a low fat whole food plant-based diet may bring about positive changes in mental health. People with signs and symptoms of mental illness should always consult their general practitioner or specialist for diagnosis and treatment.

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Further resources


Mental health and mental illness are best thought of as a spectrum. Mental health is complex and people who are mentally well will have difficulties coping at times when their life is demanding, and people with a mental illness can often function very well in certain areas of their life. Good mental health can be defined in many ways, such as finding enjoyment in usual activities, having a generally positive outlook, engaging socially and taking care of oneself.

No. Although up to 50% of people suffering from anorexia nervosa or bulimia nervosa identify as vegetarian or vegan, it is incorrect to conclude that plant-based diets contribute to these disorders. Rather, in the majority of cases, the eating disorder predates the patient’s adoption of a plant-based diet, which is used to legitimise the removal of fatty foods [7].

Orthorexia is characterised by an obsession with healthy eating to the point that the patient’s mental and physical wellbeing is compromised. As with all health-conscious dietary patterns, there is the potential for people following plant-based diets to become overly fixated on dietary restrictions. It is therefore important that patients are offered good guidance on how to implement a healthy, nutrient-rich eating pattern. A WFPB approach without caloric restriction is an ideal way to promote good health without fostering an obsessive mindset around diet [8].

  1. Lucas M, et al. (2013) Inflammatory dietary pattern and risk of depression among women. Brain Behav Immun. 2013. DOI 10.1016/j.bbi.2013.09.014. Available from:

  2. Agarwal, U. et al. (2014) A multicenter randomized controlled trial of a nutrition intervention program in a multiethnic adult population in the corporate setting reduces depression and anxiety and improves quality of life: The GEICO study. American journal of health promotion: AJHP 29(4), February 2014. doi:10.4278/ajhp.130218-QUAN-72

  3. PCRM, 2015. Food and mood: eating plants to fight the blues. Published 23rd June 2015. Available from:

  4. Chamberlain, S, et al. (2019) Treatment-resistant depression and peripheral C-reactive protein. BJS Volume 214, Issue 1 January 2019 , pp. 11-19 doi:10.1192/bjp.2018.66

  5. Bajpai, A. et al. (2014) Oxidative Stress and Major Depression. J Clin Diagn Res. 2014 Dec; 8(12): CC04–CC07

  6. Skarupski KA, Tangney C, Li H, Ouyang B, Evans DA, Morris MC. Longitudinal association of vitamin B-6, folate, and vitamin B-12 with depressive symptoms among older adults over time. Am J Clin Nutr. 2010;92(2):330-335. doi:10.3945/ajcn.2010.29413 and corresponding editorial.  

  7. Vesanto Melina RD, Brenda Davis RD. Becoming Vegetarian: The Complete Guide to Adopting a Healthy Vegetarian Diet. John Wiley & Sons; 2008.

  8. Williams, K., & Patel, H. (2020). Dietary Amino Acid Deficiency with a Restrictive Raw Vegan Diet: A Case of Orthorexia Nervosa: Lacking Lysine/Methionine Madness. International Journal of Disease Reversal and Prevention, 2(1), 6. Available from

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