Systematic reviews used to develop the 2020 to 2025 Dietary Guidelines for Americans were found to have "critically low" quality and significant methodological weaknesses, according to a new study.
In the study, published in The American Journal of Clinical Nutrition, investigators from the University of Ottawa evaluated eight systematic reviews conducted by the Nutrition Evidence Systematic Review (NESR) team that informed dietary pattern recommendations. The analysis found that all evaluated reviews were of "critically low" quality based on standardized assessment tools.
The study revealed that 74% of PRISMA 2020 checklist items and 63% of PRISMA literature search extension checklist items were satisfactorily fulfilled. However, the investigators identified multiple errors and inconsistencies in search strategies and could not reproduce searches within a 10% margin of the original results.
When examining one systematic review in depth, the assessment identified concerns regarding reporting transparency of narrative data synthesis, though no evidence of interpretation bias was found in the conclusions.
"Several methodological quality and reporting concerns were identified, which could lead to reliability and reproducibility issues should a full reproduction attempt be made," suggested lead study author Alexandra M. Bodnaruc, MSc, and her colleagues.
Critical weaknesses included the absence of meta-analyses without proper justification, a lack of protocol registration, and incomplete reporting of synthesis methods. The NESR team had determined a priori that all data synthesis would be narrative, contrary to recommended approaches.
The investigators evaluated reviews using multiple validated tools, including AMSTAR 2 for methodological quality, PRISMA 2020 and PRISMA-S for reporting transparency, and the Peer Review of Electronic Search Strategies checklist for search strategy quality.
Study limitations included an analysis of reviews from only one DGA subcommittee and partial reproduction of only one systematic review as a result of resource constraints. The investigators recommended future studies with larger sample sizes and full reproduction attempts of the systematic reviews.
The research was supported by a grant from the Nutrition Coalition, a nonprofit organization focused on evidence-based nutrition policies. The funder had no role in study design, execution, analyses, interpretation of results, or publication decisions.
For clinicians currently using the dietary guidelines in practice, the study suggested a need for careful consideration of the underlying evidence base while awaiting further research on the impact of identified methodological issues.
One author reported being a member of the 1995 DGAC. He has also published an opinion piece on the process. All other authors report no conflicts of interest.