Impact of review method on the conclusions of clinical reviews: A systematic review on dietary interventions in depression as a case in point

Abstract

Background The recommendations of experts who write 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 young 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, Web of Science, Cochrane Database of Systematic Reviews, and Google Scholar for narrative reviews and systematic reviews with and without meta-analyses on the effects of diet on depression (final search date: May 30 th , 2020). Conclusions were extracted from the abstract and discussion section and rated as strong, moderate, or weak by independent raters who were blind to study type. A benchmark on legitimate conclusion strength was based on a GRADE assessment of the highest level of evidence. This systematic review was registered with PROSPERO, number CRD42020141372. Findings 24 narrative reviews, 12 systematic reviews, and 14 meta-analyses were included. In the abstract, 33% of narrative reviews and 8% of systematic reviews came to strong conclusions, whereas no meta-analysis did. Narrative reviews were 8.94 (95% CI: 2.17, 36.84) times more likely to report stronger conclusions in the abstract than systematic reviews with and without meta-analyses. These findings were similar for conclusions in the discussion section. Narrative reviews used 45.6% fewer input studies and were more likely to be written by authors with potential conflicts of interest. A study limitation is the subjective nature of the conclusion classification system despite high inter-rater agreements and its confirmation outside of the review team. Conclusions We have shown that narrative reviews come to stronger conclusions about the benefits of a healthy diet on depression despite inconclusive evidence. This finding empirically underscores the importance of a systematic method for summarizing the evidence of a field of study. Journal editors may want to reconsider publishing narrative reviews before meta-analytic reviews are available.

Psychological Impact of COVID-19 Pandemic on Students at the University of Ibadan in Nigeria

“…Students may actually be overeating or binge-eating to cope with stress during this period. Meanwhile, as shown in a recent systematic review that there is a weak link between diet and depression, our findings also reveal nonsignificant association between food intake and depression during the pandemic [25].…”

Exploring the Impact of Flavonoids on Symptoms of Depression: A Systematic Review and Meta-Analysis

“…A recent study highlighted the importance of a systematic method for summarizing the evidence on dietary interventions in depression [ 79 ]. Currently, systematic reviews and meta-analyses have shown that unhealthy dietary patterns are associated with an increased risk of depression, while high-quality diets are related to a lower risk of depressive symptoms [ 15 , 80 ].…”

Is vegetarianism related to anxiety and depression? A cross-sectional survey in a French sample

“…The contradictory results observed in the aforementioned studies may be the consequence of many factors such as research design, sampling methodology, the nature of the nutritional measures used (self-reported or actual intake), the validity of outcome measures, and the lack of statistical controls on relevant variables. Three recent systematic reviews have provided results based on aggregated independent research studies [ 19 , 36 , 37 ]. In the first one, a large comprehensive synthesis based on eighteen studies comprising a total of 160,257 participants, it was concluded that meat-abstention was related to higher rates of risk of depression, anxiety, and related symptoms [ 38 ].…”