Table 1.

Eligibility criteria.

Inclusion Criteria

Exclusion Criteria

-Studies involving adults (people aged >18 years). -Observational studies (including cohort, longitudinal, and cross-sectional studies) and interventional studies (randomised controlled clinical trials). -Studies that focused on assessing dietary nutrient deficiencies. -The main focus was on major depressive disorder (MDD). -Papers were included regardless of the measurement methods used in the study (mainly self-reporting tools or medical diagnosis). -Articles published in English. -Studies published in the last five years (between 2018 and 2023).

-Animal studies, reviews, case reports, editorials. -Studies assessing depression as a secondary disease to another disorder and cancer. -Studies that assess depression in the context of nutrition after bariatric surgery. -Research only in paediatric and elderly populations and pregnant and/or breastfeeding women, as these are populations that would require a separate, stand-alone study on the topic described. -Studies that focused exclusively on evaluating the effectiveness of dietary interventions (for example, Western diet, Mediterranean diet, and others) or exclusively on nutrient supplementation. -Research that exclusively focusses on bipolar disorder. -Studies exclusively on depression and the gut–brain axis. -Articles published in a language other than English. -Studies published before 2018.