Describing the landscape of nutrition or diet-related randomised controlled trials: meta-research study of protocols published between 2012 and 2022

Background & Aims: The landscape of nutrition research has changed over the past decades. We aimed to map the landscape of nutrition or diet-related interventions research, using data from randomised controlled trial (RCT) protocols published in the last decade. Methods: This meta-research study examined nutrition or diet-related RCT protocols published in journals indexed in PubMed, Embase, Cinahl, Web of Science, PsycINFO, or the Global Health Database between January/2012 and March/2022. Two reviewers independently screened the titles and abstracts to check eligibility and one reviewer extracted bibliometric information, study characteristics, and research transparency practices such as protocol registration, conflicts of interest and funding disclosure. We also screened the "Instructions for Authors" of journals with publications in our sample to check for endorsement of SPIRIT, TIDieR, and CONSORT reporting guidelines, and we checked if the authors mentioned these reporting guidelines in their paper. Results: The search retrieved 62,319 records, of which 1,068 met the eligibility criteria and were included in the review. The number of published RCT protocols increased annually between 2012 and 2022, with a mean of 161 (range: 155-163) publications/ year. The USA (n = 165; 15.5%) and Australia (n = 137; 12.8%) published the largest number of protocols. Protocols were published in 148 journals, mainly medical journals (n = 518; 48.5%). Among these journals, 50 (33.8%) endorsed SPIRIT, 111 (75.3%) endorsed CONSORT, and four (2.7%) endorsed TIDieR. In 343 (32.1%) publications the authors mentioned SPIRIT, in 297 (27.8%) CONSORT was mentioned, while 20 (1.9%) mentioned TIDieR. Most protocols reported the RCT registration number (n = 1,006; 94.2%) and included statements about conflicts of interest (n = 952; 89.1%) and funding (n = 994; 93.2%). More than one third of protocols focused on adults and elderly participants (n = 350; 32.7%) and most protocols included participants with a specific clinical condition (n = 726; 68.0%). A single nutrition or diet-related intervention (n = 724; 67.8%) was described in most protocols, with "supplementation, supplements or fortification" (n = 405; 37.9%) and "nutrition education, counseling or coordination of care" (n = 354; 33.1%) being the most frequent types of interventions studied. The most frequent primary outcomes reported were related to clinical status (n = 308; 28.8%), nutritional status (n = 247; 23.1%), and frequency or severity of disease (n = 238; 22.3%). The majority of protocols described a single-centre study (n = 838; 78.5%), with two-arms (n = 844; 79.1%), parallel (n = 1014; 94.9%) design, with a superiority framework (n = 755; 70.7%). Conclusions: The number of protocols on nutrition or diet-related trials being published is increasing, indicating the importance of this type of publication. The mention of relevant reporting guidelines by both researchers and journals remains far from ideal. Most protocols assessed supplementation or fortification and nutrition education, counselling or coordination of care interventions, among adults and the elderly. ### Competing Interest Statement Flavia Moraes Silva received a postdoctoral fellowship from COPPETEC Foundation. Michael Maia Schlussel, Shona Kirtley, Jennifer A de Beyer and Gary Collins are funded by Cancer Research UK (grant C49297/A27294). Matthew J Page is supported by an Australian Research Council Discovery Early Career Researcher Award (DE200101618). Colby Vorland has received honoraria from The Obesity Society and his University has received funds to support his research from the National Cattlemen Beef Association, Alliance for Potato Research and Education, the Gordon and Betty Moore Foundation, and NIH. ### Clinical Protocols ### Funding Statement The authors have not declared a specific grant for this research from any funding agency in the public, commercial or not-for-profit sectors. ### Author Declarations I confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained. Yes I confirm that all necessary patient/participant consent has been obtained and the appropriate institutional forms have been archived, and that any patient/participant/sample identifiers included were not known to anyone (e.g., hospital staff, patients or participants themselves) outside the research group so cannot be used to identify individuals. Yes I understand that all clinical trials and any other prospective interventional studies must be registered with an ICMJE-approved registry, such as ClinicalTrials.gov. I confirm that any such study reported in the manuscript has been registered and the trial registration ID is provided (note: if posting a prospective study registered retrospectively, please provide a statement in the trial ID field explaining why the study was not registered in advance). Yes I have followed all appropriate research reporting guidelines, such as any relevant EQUATOR Network research reporting checklist(s) and other pertinent material, if applicable. Yes All data produced in the present study are available upon reasonable request to the authors