The association between dietary fiber intake and risk of lung cancer: a GRADE-assessed systematic review and dose response meta-analysis of prospective cohort studies

Earlier meta-analyses have examined the relationship between fruit and vegetable intake and risk of lung cancer; however, no study has investigated the link with fiber. Therefore, in the present systematic review and dose-response meta-analysis we aimed to summarize available findings from prospective studies on the link between dietary fiber consumption and lung cancer risk. Studies reporting risk estimates for the association between dietary fiber intake and lung cancer risk were included based on a systematic search of PubMed, Scopus, and Web of Science as well as Google Scholar up to 21 April 2025. The Newcastle–Ottawa Scale and GRADE methodology were used to assess the risk of bias and certainty of the evidence, respectively. A random-effects model was used to combine the studies’ risk estimates. Dose–response relationships were explored using a one-stage random-effects model. Prospective cohort studies with a total of 2,999,203 participants and 26,012 cases were included. According to linear dose-response analysis, each 5 g/d increase in dietary fiber intake was associated with an 8% reduction in risk of lung cancer (RR: 0.92; 95% CI: 0.85, 0.98). No evidence of a nonlinear relationship between dietary fiber intake and risk of lung cancer was observed (P-nonlinearity = 0.995). The certainty of the evidence was rated as moderate according to the GRADE rating tool. The findings of this meta-analysis support the protective association between dietary fiber intake and lung cancer risk. However, due to different limitations the results should be interpreted with caution. PROSPERO registration number: CRD420251037254.