The impact of dietary fiber consumption on human health: An umbrella review of evidence from 17,155,277 individuals

Background: Dietary fiber plays a crucial role in disease prevention through multiple protective mechanisms. While previous reviews have examined its health effects, recent advances necessitate an updated synthesis of the evidence. Objectives: This umbrella review systematically evaluates meta-analyses of observational studies to assess the strength and credibility of associations, and the quality of evidence linking dietary fiber intake to diverse health outcomes, providing a comprehensive assessment of these associations. Methods: We updated our previous umbrella review by searching major databases (October 21, 2017–December 1, 2024) for meta-analyses on dietary fiber and health outcomes. Methodological quality was assessed using AMSTAR-2 (A Measurement Tool to Assess Systematic Reviews), and evidence credibility was classified based on predefined criteria, accounting for heterogeneity (I2), small-study effects, and excess significance bias. Results: Thirty-three meta-analyses covering 38 health outcomes and 17,155,277 individuals were included. Of these, 29 (76 %) reported significant inverse associations (p < 0.05) between higher fiber intake and disease risk. Convincing evidence (Class I) was identified for cardiovascular disease (CVD) mortality, pancreatic cancer, and diverticular disease. Highly suggestive evidence (Class II) supported associations with all-cause mortality, CVD, coronary heart disease and ovarian cancer. Suggestive evidence (Class III) was observed for 16 outcomes, while six outcomes (16 %) exhibited weak evidence (Class IV). Quality assessment indicated that six meta-analyses were of high methodological quality, while others had some methodological limitations. Conclusions: Higher dietary fiber intake is associated with lower risk of multiple chronic diseases, particularly CVD mortality, pancreatic cancer, and diverticular disease. Despite these benefits, intake remains below recommended levels worldwide. Public health strategies should promote fiber-rich diets, and future research should further elucidate the role of specific fiber types in disease prevention. Systematic review registration: https://osf.io/37tyc/.