Level I | At least 1 properly conducted RCT, systematic review, or meta-analysis | Mortality | 2 good meta-analyses, 2 systematic reviews, 2 reviews of prospective cohort studies |
Morbidity (HRQOL) | Numerous RCTs and prospective clinical trials |
Interventions in weight trajectory | One meta-analysis, several RCTs, numerous traditional reviews |
Level II | Other comparison trials; non-randomized, cohort, case-control, or epidemiologic studies; and preferably more than 1 study | Population weight metrics | Primarily population-based longitudinal, prospective cohort, and cross-sectional studies |
Level III | Expert opinion or consensus statements | NA | NA |