GRADE

GRADE is a system for rating how certain we can be that an estimated effect is close to the truth. The acronym stands for Grading of Recommendations, Assessment, Development and Evaluation. It sorts the evidence for each outcome into four tiers: high, moderate, low, and very low certainty. The point readers miss most often is that these tiers describe certainty, not effect size. A high certainty rating on a small benefit still means a small benefit. A very low rating does not mean the intervention fails. It means the evidence cannot yet tell us. Randomized trials enter the assessment at high certainty. Observational evidence enters at low. Five domains can rate a body of evidence down: risk of bias, inconsistency across studies, indirectness of population or outcome, imprecision, and publication bias. Three domains can rate observational evidence up: a large magnitude of effect, a dose response gradient, and plausible confounding that would work against the observed result. Ratings are made per outcome, so one review can report high certainty for a surrogate marker and low certainty for mortality. GRADE also separates certainty of evidence from strength of recommendation, which additionally weighs benefits, harms, cost, and patient values. In longevity and nutrition most dietary evidence lands at low or very low. That is a statement about what is known, not a verdict on the diet.

Last reviewed: August 25, 2026

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