Credibility at stake: only two-thirds of randomized trials of nutrition interventions are registered and lack transparency in outcome and treatment effect definitions.

OBJECTIVE: This study aimed to investigate the adherence of randomized controlled trials of nutrition interventions to transparency practices informing assessments of selective reporting biases, including the availability of a trial registration entry, protocol and statistical analysis plan.

STUDY DESIGN AND SETTING: Retrospective observational study with cross-sectional design. We systematically searched for trials published from 1 July 2019 to 30 June 2020 and included a randomly selected sample of 400 studies. We searched for registry entries, protocols, and statistical analysis plans for all included studies. We extracted data to characterize the disclosure of sufficient information in the available materials to inform assessments of selective reporting biases, considering the definition of outcome domain, measure, metric, method of aggregation, time point, analysis population, methods to handle missing data and method of adjustment.

RESULTS: Most trials (69%) were registered, but these often lacked sufficient specification of outcomes and intended treatment effects. Protocols and statistical analysis plans provided more details, but were less often available (14% and 3%, respectively), and even then, almost all studies presented limited information to inform the assessments of risk of bias due to the selection of the reported result.

CONCLUSION: Lack of full specification of outcomes and intended treatment effects hinder a full adherence of randomized controlled trials of nutrition interventions to transparency practices and may affect their credibility.