The gut is where surrogate endpoints A lab value or measurement used in place of the outcome that matters, such as LDL cholesterol standing in for heart attacks. Moving a surrogate does not always move the outcome. are hardest to resist. Sequencing a stool sample produces a great deal of measurable change, and very little of it has been tied to an outcome anyone would feel.
Two features of the grading system matter on a page like this. A grade attaches to a use, not to a molecule, so the same compound can carry different letters for different questions. And a grade is capped by the kind of outcome the trials measured: a surrogate marker or a self-reported score cannot reach Grade A under the EBL rubric no matter how well the trial was run.
Every letter below links to its own page, where the trials, the PMIDs PubMed ID: the permanent number the US National Library of Medicine gives a published paper. Each one links to that paper's record on PubMed. and the reasons for the ceiling are set out in full.