Diets Against Depression: Strong Conclusions, Weak Evidence. A Systematic Review
16 Pages Posted: 15 Apr 2020More...
Background: The recommendations of experts who write early review articles are a critical determinant of the adaptation of new treatments by clinicians. Several types of reviews exist (narrative, systematic, meta-analytic), and some of these are more vulnerable to researcher bias than others. Recently, the interest in nutritional interventions in psychiatry has increased and many experts, who are often active researchers on this topic, have come to strong conclusions about the benefits of a healthy diet on depression. In a recent and active field of study, we aimed to investigate whether the strength of an author’s conclusion is associated with the type of review article they wrote.
Methods: Systematic searches were performed in PubMed and Web of Science for narrative reviews, systematic reviews, and meta-analyses on the effects of diet on depression (final search date September 3 rd , 2019). Conclusions were extracted and rated as strong, moderate, or weak by independent raters who were blind to study type. A benchmark on valid conclusion strength was based on a GRADE assessment of the highest level of evidence.
Findings: 19 narrative reviews, 10 systematic reviews, and 12 meta-analyses were included. 42% of narrative reviews and 20% of systematic reviews came to strong conclusions, whereas no meta-analysis did. Narrative reviews were 7·90 (95% CI: 2·04, 30·57) times more likely to report stronger conclusions than systematic reviews and meta-analyses. Narrative reviews used 45·5% fewer input studies and were more likely to be written by authors with potential conflicts of interest. The latter was also associated with the formulation of stronger conclusions.
Interpretation: We have shown that narrative reviews tend to overstate the benefits of a healthy diet on depression, but the phenomenon may occur with all new treatments. Journal editors may want to reconsider publishing narrative reviews before meta-analytic reviews are available.
Funding Statement: This project was not funded.
Declaration of Interests: Without relevance to this work, P. Molero reports to have received research grants from the Ministry of Education (Spain), the Government of Navarra (Spain), the Spanish Foundation of Psychiatry and Mental Health and AstraZeneca; he is a clinical consultant for MedAvanteProPhase and has received lecture honoraria from or has been a consultant for AB-Biotics, Janssen, Novumed, Roland Berger, and Scienta. The other authors declare no competing interests.
Ethics Approval Statement: As a guideline for conducting and reporting this systematic review, we followed the PRISMA statement. A protocol for this review is registered at PROSPERO (currently under revision).
Keywords: Diet; Nutrition; Mental health; Depression; Bias; Conflicts of Interest; Systematic review; Meta-analysis
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