A scoping review of 175 primary studies, drawn alongside 20 systematic reviews within 2 umbrella reviews, identified 51 dietary quality indices. The five most common were MedDiet scores, AHEI, DASH, HEI, and the Dietary Inflammatory Index. Higher diet quality was linked to better outcomes for all-cause mortality, cardiovascular disease, type 2 diabetes, and cancer across 17 meta-analyses. AHEI-2010 and DII were altered in nearly every study, DASH and HEI-2015 in about half. Meta-regression found no meaningful link between degree of modification and effect size.
The reassuring reading is that the signal is robust: whether researchers tweak food groups, cutoffs, or components to fit local eating patterns, healthier diets keep predicting lower risk. That fits what other work shows, where very different scores converge on the same advice of more plants, whole grains, and fish, and fewer processed foods and sugary drinks. For readers, the practical takeaway is that no single named diet is required; the shared pattern matters more than the label. The caveats are real, though. Many studies reported composition poorly, so the meta-regression only covers those that disclosed details, and modifications were mostly adaptations to local data rather than random changes. The evidence is observational, so residual confounding by healthy-user behaviour remains. Reproducibility is the genuine casualty, since results cannot be cleanly compared across cohorts. This is a confirmatory, methodologically useful paper rather than a new finding, and its call for standardised scoring is well founded.