Dietary fiber density and incident gross motor limitation among middle-aged and older adults: a prospective cohort analysis.

Introduction: Preserving physical function is a central goal of ageing research, yet the dietary factors that precede early motor limitation remain incompletely defined. Methods: Here we examined whether dietary fiber density was associated with incident gross motor limitation in the 2013 Health Care and Nutrition Study linked to the Health and Retirement Study. Among 5,388 adults aged 50 years or older who were free of gross motor limitation at baseline, 2,018 developed incident limitation during biennial follow-up through 2022. Results: In the fully adjusted modified Poisson model, each 1-s.d. increment in fiber density was associated with a risk ratio of 0.86 (95% CI, 0.82 to 0.90), and the highest versus lowest quartile had a risk ratio of 0.72 (95% CI, 0.64 to 0.81). Augmented inverse probability weighting estimated a 9.0 percentage-point lower absolute risk in the highest versus lowest quartile. Estimates were unchanged after multiple imputation for missing covariates. In Fine-Gray models treating death as a competing event, the subdistribution hazard ratio was 0.82 per 1-s.d. increment (95% CI, 0.77 to 0.87). Results were also consistent across alternative exposure and outcome definitions, interval-aware models, diet-pattern adjustment and secondary functional outcomes. Conclusion: Higher fiber density was consistently associated with lower functional-limitation risk, but it may index a broader constellation of dietary and lifestyle factors; causal effects cannot be inferred.