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Table 1 Grading system and evidence strategies

From: International Society of Sports Nutrition Position Stand: nutritional considerations for single-stage ultra-marathon training and racing

Evidence categorySources of evidenceDefinition
AMeta-analyses, position-stands, and randomized-controlled trials (RCTs)Evidence from meta-analyses, position stands, and well-designed RCTs (or trials that depart only minimally from randomization) that provide a consistent pattern of findings in the population for which the recommendation is made.
BSystematic reviews including RCTs of limited numberEvidence from endpoints of intervention studies that include only a limited number of RCTs, post hoc or subgroup analysis of RCTs. In general, Category B is relevant when few randomized trials exist, they are small in size, and/or the trial results are somewhat inconsistent.
CNonrandomized trials/observational studies, other reviews (e.g., narrative)Evidence from outcomes of uncontrolled/nonrandomized trials or from observational studies. Reviews that may harbour a specific narrative.
DCase-reportsEvidence from low number or single-subject designs that report on unique observations or events, not necessarily applicable to broader populations.