According to a comprehensive, systematic review of previous studies, a diet of vegetables, fruits, nuts, plant-based food and fish — typical of a Mediterranean diet — could help lower risk of depression.

“With depression being the psychiatric disorder incurring the largest societal costs in developed countries, there is a need to gather evidence on the role of nutrition in depression, to help develop recommendations and guide future psychiatric health care,” said University College London researcher Camille Lassale and co-authors.

“The aim of our review was to synthesize the link between diet quality, measured using a range of predefined indices, and depressive outcomes.”

Dr. Lassale and colleagues analyzed data from a total of 20 longitudinal and 21 cross-sectional studies.

“We aggregated results from a large number of studies and there is a clear pattern that following a healthier, plant-rich, anti-inflammatory diet can help in the prevention of depression,” they noted.

Of the 41 studies included in the review, four specifically looked at the link between a traditional Mediterranean diet and depression over time in 36,556 adults.

The team found that participants from these longitudinal studies with greater adherence to a traditional Mediterranean diet had a 33% lower risk of developing depression than people whose diet least resembled a Mediterranean diet.

The findings also showed that a pro-inflammatory diet with high contents of saturated fat, sugar and processed food was associated with a higher risk of depression in five longitudinal studies of 32,908 adults from France, Australia, Spain, the United States and the United Kingdom.

“Avoiding pro-inflammatory foods and favoring anti-inflammatory foods rich in plant fiber, vitamins, minerals and polyphenols, such as fruits, vegetables, legumes, fish, olive oil and nuts, may reduce the risk of depressive disorders,” the scientists said.

“A pro-inflammatory diet can induce systemic inflammation, and this can directly increase the risk for depression,” Dr. Lassale said.

“There is also emerging evidence that shows that the relationship between the gut and brain plays a key role in mental health and that this axis is modulated by gastrointestinal bacteria, which can be modified by our diet.”

“By showing that an adherence to healthy dietary patterns is associated with a reduced risk of depressive disorders, we contribute to the growing body of evidence regarding the importance of our daily diets to our mental and brain health,” added Dr. Tasnime Akbaraly, from the University Hospital of Montpellier and University College London.

“Added to recent randomized trials showing beneficial effects of dietary improvement on depression outcomes, there are now strong arguments in favor of regarding diet as mainstream in psychiatric medicine.”

The review paper was published online September 26 in the journal Molecular Psychiatry.

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Camille Lassale et al. Healthy dietary indices and risk of depressive outcomes: a systematic review and meta-analysis of observational studies. Molecular Psychiatry, published online September 26, 2018; doi: 10.1038/s41380-018-0237-8