Have vegetarian or vegan diets been shown to help people with mental illness?

Question

I recently had a discussion with a friend who struggles with mental health, and that friend was planning to try a more plant-based diet (or even a totally plant-based diet) in an attempt to improve their mental health.

Have there been any studies showing that vegetarian, vegan, or plant-based diets providing a beneficial effect to people who are living with diminished mental health or mental illness? If yes, which diet patterns have been shown to be more or less effective?

I'm looking for scientific studies, so answers with DOI links are strongly preferred.

Answer 1

The most well-studied diet pattern regarding mental health is the Mediterranean diet pattern, which has shown in multiple small studies to reduce the severity of the symptoms of depression and even allow psychiatric medications to work better. This is most likely because the Mediterranean diet pattern naturally contains many nutrients that are recommended for depression, such as fish oil, magnesium, zinc, folate, vitamin B12, and lots of fruits and vegetables.

Vegetarian diets are typically high in many of those as well (with the exception of B12 and fish oil).

The effect of a vegan diet on mental health is not established. This is because studies have had inconsistent results, with some reporting that vegans have a much higher rate of depression than omnivores, and others stating their rate is lower! The studies that showed higher rates of depression among vegans were unable to conclude if individuals with depression were more likely to choose a vegan diet, or if there was a dietary component to the depression.

Here are a few studies that I was able to get to quickly.

• Effects of omega-3 fatty acid supplementation on mood and emotional information processing in recovered depressed individuals
• Adherence to the Mediterranean diet and risk of depression: a systematic review and updated meta-analysis of observational studies
• Fruit, Vegetable, and Antioxidant Intakes Are Lower in Older Adults with Depression
• Is meat consumption associated with depression? A meta-analysis of observational studies
• Mediterranean diet and depression
• Depressive Symptoms and Vegetarian Diets: Results from the Constances Cohort
• Vegetarian diets and depressive symptoms among men

Another thing to consider is the use of probiotics to improve gut health. Some studies have begun to indicate that probiotics (and prebiotics) can really work towards improving our mental health [1, 2, 3]