Mental health is essential to our overall well-being. Mental health encompasses our emotional, psychological, and social well-being. It impacts the way we think, feel, handle stress, and make decisions. Many studies have shown the benefits of vegetarianism on our physical health, such as prevention of cardiovascular disease, diabetes, and cancer, but what does the research say about vegetarianism on our mental health?
In this article we explain (in plain English!) the conclusions of scientific studies that have looked at vegetarian mental health.
Vegetarian diets consist of plant-based foods rich in whole grains, legumes, nuts, seeds, fruits, and vegetables, while avoiding red meat, processed meat products, refined foods, and sweets.
There are several variations of a vegetarian diet:
Benefits of Vegetarianism on Mental Health
In the sections that follow we highlight studies that have linked vegetarianism with improved mood, reduced psychological disorders (anxiety and depression), improved sleep quality, cognitive function, and look at the mechanism of how plant-based foods act on our mental health.
A vegetarian diet may have a positive impact on your mood. Researchers from Cornell University conducted a “Nutritional and Mood assessment of a 30-day vegan diet” on non-vegetarians. Participants reported a significant change in mood, with greater physical strength, enthusiasm and energy when switching to a vegan diet (Olabi et al., 2015).
A study conducted by Beezhold & Johnston (2012) reported that omnivores who restricted meat, fish and poultry and followed a vegetarian diet for two weeks showed an increase in mood scores using the Profile of Mood States questionnaire and the Depression Anxiety and Stress Scales.
Another study published in the journal Nutritional Neuroscience reported that “a strict plant-based diet does not appear to negatively impact mood; a reduction of animal food intake may have mood benefits” (Beezhold et al., 2014).
According to Głąbska et al. (2020), adding more fruits and vegetables to your diet can enhance your mental health “any increase in the consumption of fruits and vegetables results in the improvement of well-being, enhances happiness, and decreases depressive symptoms”.
These studies support the fact that a vegetarian diet may have a beneficial impact on improving your mood.
Decreased Risk of Psychological Disorders (Anxiety & Depression)
Several academic papers have shown the positive benefits of following a plant-based diet high in whole grains, fruits, vegetables, legumes, and nuts on psychological disorders such as anxiety and depression.
A study published in the European Journal of Clinical Nutrition, investigated the link between depressive symptoms and dietary habits of mid-aged women in 2001 and 2004, those who adhered to a Mediterranean diet exhibited a lower frequency of depressive symptoms “Consumption of a ‘Mediterranean-style’ dietary pattern by mid-aged women may have a protective influence against the onset of depressive symptoms” (Rienks et al., 2012).
Substituting a Mediterranean-style diet with fish oil may improve depression. Scientists at the University of South Australia found that participants who suffered from depression and changed to a Mediterranean diet supplemented with fish oil for three months reported a higher reduction in depression and enhanced mental health scores (Parletta et al., 2019).
A paper published in the journal of Clinical Nutrition, looked at the effect of a healthful plant-based diet and unhealthful plant-based diet on anxiety, depression, psychological distress, and obesity in Iranian women. They reported that women who followed a healthy plant-based diet were less likely to suffer from anxiety and depression, compared to women who followed an unhealthful plant-based diet. Those following an unhealthful plant-based diet were also more likely to be obese “A plant-based diet, particularly healthful-rich plant foods were inversely associated with psychological disorders” (Zamani et al., 2020).
A plant-based diet coupled with exercise may be beneficial in treating individuals who suffer from moderate to severe depression and anxiety “an intervention of diet, exercise, lifestyle and behaviour modification may provide considerable benefits for moderate to severe depression and anxiety” (Null & Pennesi, 2017).
A study exploring the relationship between a vegetarian diet and depression among South Asians living in the United States found that participants following a vegetarian diet were less likely to suffer from depression “43% lower odds of depression among vegetarians” (Jin et al., 2021).
This is further supported by Daneshzad et al. (2019) who stated “higher adherence to a healthful plant-based diet is associated with lower odds of mental disorders” and Lai et al. (2013) who reported “high intakes of fruit, vegetables, fish, and whole grains may be associated with a reduced depression risk”.
This evidence clearly shows the positive impact a vegetarian diet can have on anxiety, depression and psychological distress.
Cognitive Function and Alzheimer’s disease
Healthful plant-based foods play a role in healthy brain ageing. Westernized diets which are high in inflammatory causing compounds may lead to an increased risk of dementia, caused by Alzheimer’s disease (AD). Alzheimer’s disease is the most common neurodegenerative disease in the world.
Fruits, vegetables and seafood have protective effects on brain health “Among specific foods with evidence of neuroprotection are green leafy vegetables, other vegetables, berries, and seafood” While high saturated fat diets associated with animal products have a negative impact on cognitive health “Diets high in saturated and trans fats have been shown to increase cognitive decline and the risk of developing dementia” (Morris, 2016).
According to Gregorevic (2022) a vegetarian diet is the best way to protect your brain from degeneration “the key is eating a large variety of plant-based foods and ensuring that the diet contains all necessary micronutrients”.
Improved Sleep Quality
A good night’s sleep is essential for our bodies to recover from the day’s stresses, it is also important for our brains. Lack of quality sleep and insomnia may lead to irritability and psychological disorders. Poor sleep duration and quality could also lead to an increased risk of cardiovascular disease (Javaheri & Redline, 2012).
Plant-based diets may have a positive impact on our sleep. A paper published in the journal Sleep, reported that participants who followed a Mediterranean diet were more likely to have a good night’s sleep “Mediterranean-style diet is associated with adequate sleep duration, less insomnia symptoms, and less likely to have insomnia accompanied by short sleep” (Castro-Diehl et al., 2018).
This evidence is backed-up by Mamalaki et al. (2018) who reported that participants who followed a Mediterranean diet had a better quality sleep “sleep quality is associated with Mediterranean diet adherence”.
Researchers at Cambridge University investigated the link between a plant-based diet and sleep and mental health status in diabetic women “patients who adhered to animal-based diets rather than plant-based diets were more likely to be poor sleepers and have mental health disorders” (Daneshzad et al., 2019).
Mechanism of Plant-Based Diet on Mental Health
This section looks at the mechanism at which plant-based foods affect our mental health.
Inflammation and Oxidative Stress
Plant-based diet plays an essential role on mental health by preventing inflammation and oxidative stress.
Inflammation and oxidative stress are thought to cause changes to the healthy functioning of the brain leading to a negative impact on mental health “Oxidative damage in the brain causes nervous system impairment; oxidative stress has also been implicated in depression, anxiety disorders and high anxiety levels” (Black et al., 2019; Bouayed et al., 2009).
High levels of inflammation is thought to activate feelings of sadness “Inflammation can trigger melancholic symptoms through activation of inflammatory pathways in the brain” (Slavich & Irwin, 2014).
Anti-oxidant and Anti-inflammatory Effect
Vegetarian diets rich in plant-based foods abundant in antioxidants and polyphenols are able to protect the body from inflammation and oxidative stress “Vegetarian diets are inherently rich in antioxidants, and adherence to vegetarian diets is associated with low oxidative stress” (Johnston, 2017).
Polyphenols are a natural compound found in food sources such as berries, nuts, coffee and tea “polyphenols affect a broad range of mechanisms in the brain that can assist in the maintenance of cognitive and mental health, as well as the recovery from neurodegenerative diseases” (Gomez-Pinilla & Nguyen, 2012).
Folate and magnesium, nutrients that are abundant in plant food sources, aid in the production of neurotransmitters such as serotonin and dopamine (‘happy hormones’). Magnesium has strong anti-inflammatory effects – low levels of magnesium in the body may cause the on-set of depression (Rao et al., 2008).
Recently, we are learning more about the important role our gut microbes play on our mental health “There is now over-whelming evidence to support the fact that gut microbes have a major impact on central neurochemistry and behaviour, especially stress-related disorders such as depression” (Dinan et al., 2019).
A healthy microbiome (The trillions of bacteria and yeasts that live in our gut) is essential for proper brain function and mental health (Foster & Neufeld, 2013). Stress and high-fat diets may affect the healthy balance in your gut and may lead to psychological disorders such as anxiety and depression, and illness.
Diet influences the gut microbiome. Plant foods such as onion, chicory, garlic, banana, and asparagus act as prebiotics (foods containing fructo-oligosaccarides that help the good gut microbes grow) and may alleviate anxiety and depression. (Sabater-Molina et al., 2009; Taylor & Holscher, 2020).
Polyphenols, which are abundant in vegetarian diets rich in fruits, vegetables, coffee and tea are beneficial in controlling the composition of the gut microbiome.
Plant-based foods provide healthy nutritious fuel for our ‘good’ gut microbes to grow and thrive, and prevent harmful pathogenic bacteria from surviving which could cause an in balance leading to inflammation and in turn affecting our mental health.
Possible Drawbacks of Vegetarianism on Mental Health
A few papers have suggested that vegetarian diets do not have an impact on mental health.
A research paper published in the Journal of Affective Disorders found no link between a vegetarian diet and mental health in US, Russian and German individuals, however a small rise in anxiety and depression among Chinese students was reported “Vegetarianism is not associated with mental health in the US, Russia, or Germany, but is associated with anxiety and depression in China” (Lavallee et al., 2019).
A paper published in Nutrition Reviews found that vegetarian diets lead to an increase in depression, while anxiety decreased, mainly among individuals younger than 26 years “Vegan or vegetarian diets were related to a higher risk of depression and lower anxiety scores” (Iguacel et al., 2021).
It has been suggested that the reason for these conflicting studies could be due to the fact that participants who reported following a vegetarian diet may not have been following a balanced, healthful plant-based diet, but a plant-based diet consisting largely of refined grains, sweets, potatoes, fruit juices, and sweetened beverages.
A healthful-rich plant-based diet is essential for optimal mental health; it is linked to reduced rates of depression, provides a beneficial effect on our gut microbiome, and studies suggest that certain plant foods have an anti-depressant effect on our brains (Dinan et al., 2019).
A well-planned, balanced, nutritious vegetarian diet that is rich in healthful plant-based foods full of fiber and antioxidants, and low in red and processed meats, and refined sugars can provide your body with the defences it needs to keep depression at bay and ensure your body and mind stay happy and healthy for a long time.
Mental Health Benefits Studies
Mental Health Benefits of Vegetarianism