Blue Monday: are fruit and vegetables beneficial for mental health?

As an essential dimension of health, mental health is still insufficiently taken into account in our societies and health systems. On Blue Monday – supposedly the most depressing day of the year – Aprifel looks back at a recent study that examined the available evidence on the influence of fruit and vegetable consumption on mental health in adults. This systematic review of the literature confirms existing data and shows a positive association between fruit and vegetable consumption and mental health.

Mental health and its disorders (see box) are an essential component of health and have a significant impact on all aspects of life. Mental health disorders are increasing worldwide and have been particularly exacerbated by the Covid-19 pandemic and the economic crisis (WHO, 2022). Therefore, understanding the determinants of mental health, especially identifying the levers for its preservation, is an important issue.

While the protective role of a healthy, varied diet rich in fruits and vegetables on chronic diseases is now well established, scientists are also interested in its impact on mental health. Thus, various studies have concluded that healthy eating habits maintain better well-being and reduce the risk of mental disorders in adolescents and students (Fujii, 2016; Tanaka, 2019). A systematic review of the literature (Głąbska et al, 2020) conducted in 2020 complements this knowledge in adults.

A positive association between fruit and vegetable consumption and mental health

This review included 61 studies from different countries and examined the influence of fruit and vegetable consumption on 3 types of parameters of mental health (see table below):

• General outcomes
• Variables reflecting a healthy mental state
• Indicators showing its degradation

Overall, most studies show that fruit and vegetable consumption was statistically associated with mental health.

Numerous studies have also found that any increase in fruit and vegetable consumption leads to an improvement in well-being, increases happiness and decreases depressive symptoms, with the strongest effect being observed for 6 to 8 servings per day depending on the study. Thus, this work suggests that the general recommendation to consume at least 5 servings of fruits and vegetables per day would also be beneficial for mental health.

Specific effects are observed for certain categories of fruits and vegetables

Some of the studies reviewed in this work not only show the global positive influence of fruit and vegetables on mental health, but also highlight the more specific effect of certain categories. The following raw fruits and vegetables have been associated with better mental health: bananas, apples, citrus fruits, berries, grapefruit, kiwi, carrots, lettuce, cucumber, and green leafy vegetables, especially spinach.

There is also evidence in the literature that higher total fruit and vegetable consumption – including berries, citrus fruits, and green leafy vegetables – is associated with higher levels of optimism and self-esteem, as well as reduced levels of psychological distress and risk of depression.

The mechanism of action is still unknown

Despite this growing body of research, there is still no clear explanation regarding the positive influence of fruit and vegetable consumption on mental health. Also, the mechanism behind the particular effect observed for certain categories is still unknown.

Three hypotheses are currently favored:

• The positive effect of fruit and vegetable consumption is linked to their high content of specific nutrients that play a positive role in mental health: complex carbohydrates, fiber, vitamins C and B, carotenoids, potassium and polyphenols.
• A better level of mental health could promote healthier eating habits, including a higher consumption of fruit and vegetables.
• There is a psychological explanation: a better diet, especially a higher consumption of fruit and vegetables, could promote positive emotions and therefore better mental health.

Further studies are needed to confirm and extend these findings

This review confirms the available literature on the potential benefits of high fruit and vegetable consumption on mental health. However, authors recommend that research efforts be continued. Indeed, only experimental studies will provide clear evidence that fruit and vegetable consumption influences mental health, as reverse causality is also possible. Lastly, other limitations in current knowledge are also pointed out by the authors:

• There was no consistent definition of fruits and vegetables in the studies reviewed, which limits the scope of the findings.
• Some components of mental health and some populations were not included in this work, namely people with intellectual disabilities, dementia and eating disorders.

Further work is needed to provide a global understanding of mental health in diverse populations using a standardized method.