Does the evidence support a relationship between higher levels of nut consumption, lower risk of depression, and better mood state in the general population? A systematic review

Dietary patterns play a key role in mental health, depression, and mood state. However, the evidence concerning specific foods highly recommended for mental health, such as nuts, has not yet been synthesized.The objective of this review was to synthesize the evidence for a relationship between higher levels of nut consumption, lower risk of depression, and better mood state in the general population.The MEDLINE, Scopus, Cochrane Central, Web of Science, and PsycInfo databases were systematically searched from each database's inception to March 2021.Randomized clinical trials (RCTs) and observational studies exploring the association between nut consumption, level of depression, and mood state in the general population were included. The quality of the studies was measured through the Joanna Briggs Institute tool (cross-sectional studies), the NIH Quality Assessment Tool (cohort studies), and the Cochrane Risk-of-Bias tool (RCTs). The Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines were followed.A total of 10 studies involving 66 418 individuals were included, of which 3 were cross-sectional, 3 were cohort studies, and 4 were RCTs. In studies concerned with depression (n = 6 studies), a higher level of nut consumption was associated with a lower risk of depression in 2 cross-sectional studies and 1 cohort study, while a similar but nonsignificant association was found in another cohort and in two RCTs. In studies concerned with mood state (n = 4), 1 cohort study reported an association between higher nut consumption and significant improvement in mood state, whereas (nonsignificant) associations between higher nut consumption and increased negative feelings were reported in a cross-sectional study and two RCTs.Despite the small number of studies and the limitations related to them, such as reverse causation bias, overall, the available literature suggests that higher nut consumption could be associated with a lower risk of depression, fewer depressive symptoms, and better mood state in the general population.PROSPERO registration no. CRD42021241070.