Issues related to the conduct of systematic reviews: a focus on the nutrition field

Systematic reviews (SRs) are an increasingly popular evidence-based tool and are often used to answer complex research questions across many different research domains. Early SR methodology was advanced by social scientists, and the term meta-analysis was coined by a social scientist who also conducted research in psychology. SRs have recently become popular in healthcare and are likely to be beneficial in any field. The aim of this report is to highlight issues in SR conduct with a focus on the field of nutrition and to make recommendations on improving SR conduct in this area. Development of the research question is probably the most important step in conducting an SR. The 4 main components of an answerable question are 1) the patient, population, or problem; 2) the intervention, independent variable, or exposure; 3) the comparators; and 4) the dependent variables or outcomes of interest. The question will be used to determine the optimal methods for conducting the SR. SRs often include study designs beyond randomized trials and do not always include a meta-analysis of the results. Other topics explored include understanding and interpreting discordant reviews and the importance of reporting tools [eg, QUality Of Reporting Of Meta-analyses (QUOROM Statement) or CONsolidated Standards Of Reporting of Trials (CONSORT Statement)]. Recommendations are then provided, such as developing a capacity-building program, searching the primary literature for research gaps, and extending reporting tools such as the QUOROM Statement to the field of nutrition.