Examining the Relation Between Dietary Sodium Indexed to Fiber and Heart Rate Variability in Apparently Healthy Adults

Background: Diet is a major modifiable risk factor for cardiovascular disease (CVD), the leading cause of death in America. Notably, high sodium (Na + ) and low fiber consumption are both associated with hypertension, impaired autonomic function, and obesity, which all contribute to CVD. However, it is unknown whether there are interactions between Na + indexed to fiber (i.e., Na + /Fiber) and autonomic balance and body composition. Heart rate variability (HRV) is a tool commonly used to indirectly assess autonomic regulation. Thus, we examined the relation between Na + /Fiber with HRV and body composition in apparently healthy adults. Methods: Habitual Na + /Fiber was assessed in 41 adults (19M/22F, age: 24(24) yrs, body mass index (BMI): 27(6) kg/m 2 , data expressed as median (interquartile range)). We collected average Na + /Total Fiber and Na + /Soluble Fiber from three day food and fluid diaries (two week days and one weekend day), and utilized Nutrition Data System for Research software for nutrient analysis. We collected resting supine (≥ 5-min) single lead chest electrocardiogram data, which was imported to Kubios HRV Scientific Lite v4.1.1 We derived HRV in the time domain including standard deviation of normal-to-normal R-R intervals (SDNN) and root mean square of successive differences (RMSSD); and frequency domain (% for all) including very low frequency (0.0033–0.04 Hz,VLF), low frequency (0.04–0.15 Hz, LF), high frequency (0.15–0.40 Hz, HF), and LF:HF. We also examined anthropometric measures, including waist circumference, waist:hip, and BMI. Spearman's rho (ρ) was used to assess correlations between Na + /Fiber with HRV and anthropometric variables. We set α to ≤ 0.05 a priori. Results: Na + /Total Fiber was not correlated with SDNN (69.9(38.2), ρ=0.181, p =0.262), RMSSD (80.6(44.1), ρ=0.254, p =0.114), nor LF:HF (0.938(0.835), ρ=0.120 p =0.478). Na + /Total Fiber was correlated with waist circumference (86(18), ρ=0.329; p =0.036) but not waist:hip ratio (0.83(0.13), ρ=0.302, p =0.055) or BMI (ρ=0.221, p =0.164). Similar to Na + /Total Fiber, Na + /Soluble Fiber was not correlated with SDNN (ρ=0.144, p =0.382), RMSSD (ρ=0.231, p =0.157), nor LF:HF (ρ=0.155, p =0.365). Na + /Soluble Fiber was correlated with anthropometrics including waist circumference (ρ=0.338, p =0.033) and BMI (ρ=0.307, p =0.054). However, Na + /Soluble Fiber was not correlated with waist:hip (ρ=0.298, p =0.062). Conclusion: In our cohort, neither habitual Na + /Total Fiber nor Na + /Soluble fiber were correlated with any HRV measures. While Na + /Total Fiber and Na + /Soluble Fiber appear to be associated with cardiometabolic risk (i.e., body composition), the do not seem to influence autonomic balance in apparently healthy adults. Funding Source: This research was supported by the National Institutes of Health (NIH) K01 [HL147998] and CCTS Pilot funding [UL1TR003096]. This abstract was presented at the American Physiology Summit 2025 and is only available in HTML format. There is no downloadable file or PDF version. The Physiology editorial board was not involved in the peer review process.