Perspective: Design and Conduct of Human Nutrition Randomized Controlled Trials.

In the field of human nutrition, randomized controlled trials (RCTs) are considered the gold standard for establishing causal relations between exposure to nutrients, foods, or dietary patterns and prespecified outcome measures, such as body composition, biomarkers, or event rates. Evidence-based dietary guidance is frequently derived from systematic reviews and meta-analyses of these RCTs. Each decision made during the design and conduct of human nutrition RCTs will affect the utility and generalizability of the study results. Within the context of limited resources, the goal is to maximize the generalizability of the findings while producing the highest quality data and maintaining the highest levels of ethics and scientific integrity. The aim of this document is to discuss critical aspects of conducting human nutrition RCTs, including considerations for study design (parallel, crossover, factorial, cluster), institutional ethics approval (institutional review boards), recruitment and screening, intervention implementation, adherence and retention assessment, and statistical analyses considerations. Additional topics include distinguishing between efficacy and effectiveness, defining the research question(s), monitoring biomarker and outcome measures, and collecting and archiving data. Addressed are specific aspects of planning and conducting human nutrition RCTs, including types of interventions, inclusion/exclusion criteria, participant burden, randomization and blinding, trial initiation and monitoring, and the analysis plan.