Evaluating Concordance of Bodies of Evidence From Randomized Controlled Trials, Dietary Intake and Biomarkers of Intake in Cohort Studies: A Meta-Epidemiological Study.

We aimed to identify and compare empirical data to determine the concordance of diet-disease effect estimates of bodies of evidence (BoE) from randomized controlled trials (RCTs), dietary intake and biomarkers of dietary intake in cohort studies (CSs). The Cochrane Database of Systematic Reviews and MEDLINE were searched for systematic reviews (SRs) of RCTs, and SRs of CSs that investigated both dietary intake and biomarkers of intake published between 01.01.2010 and 31.12.2019. For matched diet-disease associations, the concordance between results from the three different BoE was analyzed using two definitions: qualitative (e.g., 95% CI within a pre-defined range), and quantitative (test hypothesis on the z score). Moreover, the differences in the results coming from BoERCTs, BoECSs dietary-intake, and BoECSs biomarkers were synthesized to get a pooled ratio of risk ratio (RRR) across all eligible diet-disease associations, so to compare the three BoE. Overall 49 diet-disease associations derived from 41 SRs were identified and included in the analysis. 24%, 10%, 39% of the diet-disease associations were qualitatively concordant comparing BoERCTs vs. BoECSs dietary-intake, BoERCTs vs. BoECSs biomarkers and comparing both BoE from CSs, respectively. 88%, 69%, 90% of the diet-disease associations were quantitatively concordant comparing BoERCTs vs. BoECSs dietary-intake, BoERCTs vs. BoECSs biomarkers and comparing both BoE from CSs, respectively. The pooled RRR comparing effects from BoERCTs with effects from BoECSs dietary-intake was 1.09 (95% CI 1.06, 1.13), and RRR: 1.18 (95% CI 1.10, 1.25) compared to BoECSs biomarkers. Comparing both BoE from CSs, the difference in the results was also small (RRR: 0.92; 95% CI: 0.88, 0.96). Our findings suggest that BoE from RCTs and CSs are often quantitatively concordant. Prospective SRs in nutrition research should include whenever possible BoE from RCTs, and CSs on dietary intake and biomarkers of intake to provide the whole picture for an investigated diet-disease association. Statement of significance: Our findings suggest that bodies of evidence from randomized controlled trials and cohort studies are often concordant.