This new systematic review and meta analysis from Magali Rios-Leyvraz and Jason Montez was funded by the WHO and supported by the government of Japan and will form the basis for their upcoming recommendations. 283 studies were included in the review. Meta-analyses focused on randomized controlled trials, prospective cohort studies and case–control studies assessing cancer, and certainty in results was assessed via GRADE (Grading of Recommendations Assessment, Development and Evaluation).