# Association Between Dietary Fiber Intake and Inflammatory Biomarkers in U.S. Adults: A Cross-Sectional Analysis of the Pre-COVID-19 National Health and Nutrition Examination Survey 2017–2018

## TL;DR

Higher dietary fiber intake is linked to lower inflammation in U.S. adults, based on pre-pandemic health data.

## Contribution

This study provides nationally representative evidence of fiber's anti-inflammatory effects in U.S. adults using recent NHANES data.

## Key findings

- Each 5g/day increase in fiber was associated with 4-7% lower hs-CRP levels.
- Top fiber quartile showed 20.7% lower hs-CRP and 47% lower odds of elevated inflammation.
- Fiber intake also reduced white blood cell and neutrophil counts, suggesting lower inflammation.

## Abstract

Background/Objectives: Dietary fiber has been associated with lower levels of inflammatory biomarkers, but nationally representative evidence using recent U.S. data remains limited. We evaluated the association between dietary fiber intake and inflammatory biomarkers in U.S. adults using the National Health and Nutrition Examination Survey (NHANES) 2017–2018, the last fully completed cycle before the COVID-19 pandemic, providing a pre-pandemic benchmark for future comparisons. Methods: We analyzed 3570 adults (≥20 years) from NHANES 2017–2018 with complete dietary and biomarker data. Fiber intake was averaged from two 24 h recalls. Outcomes included serum high-sensitivity C-reactive protein (hs-CRP; primary outcome), white blood cell count (WBC), and neutrophil count. Survey-weighted regression models adjusted for demographic, socioeconomic, lifestyle, clinical, and dietary covariates. Associations were examined continuously (per 5 g/day fiber), by quartiles, and with restricted cubic splines. Sensitivity analyses excluded participants with cardiometabolic conditions or modified covariate sets. Results: Each 5 g/day higher fiber intake was associated with 4–7% lower hs-CRP (p < 0.001). Participants in the highest versus lowest fiber quartile had 20.7% lower hs-CRP (95% CI −27.1, −14.4) and 47% lower odds of elevated hs-CRP (OR 0.53, 95% CI 0.32–0.85). Secondary outcomes showed significant inverse associations: each +5 g/day was associated with −0.98% WBC (95% CI −1.84, −0.13; p = 0.024) and −1.44% neutrophils (95% CI −2.62, −0.26; p = 0.017) in fully adjusted models. Spline analyses showed no nonlinearity for WBC (p = 0.227) but nonlinear inverse associations for neutrophils (p = 0.0017). Sensitivity analyses confirmed robustness to exclusion of individuals with diabetes, hypertension, or hyperlipidemia, and to alternative covariate specifications. Conclusions: Higher dietary fiber intake was independently associated with a more favorable inflammatory biomarker profile (hs-CRP, WBC, and neutrophils) in U.S. adults, providing a pre-pandemic benchmark for future comparisons. Longitudinal and interventional studies are needed to clarify temporality and causality.