The effect of resistant starch on heart rate variability in women with metabolic risks: a subgroup analysis from a randomized, double-blind, clinical trial

Background: Heart rate variability (HRV) is a well-established marker of autonomic nervous system function and resistant starch (RS) is known to modulate gut microbiota and promote short-chain fatty acid production. This study aimed to investigate whether RS consumption improves HRV by modulating autonomic function in individuals with metabolic syndrome risks. Methods: This randomized controlled trial included 30 women with metabolic syndrome, recruited from a university hospital. Participants were randomly assigned to either the high-resistant starch (HRS) group or the low-resistant starch (LRS) group. The intervention lasted for 8 weeks. The primary analysis of this study focused on participants in the lower 50% of baseline total power (TP), assessing the differential effects of HRS intake on autonomic function in this subgroup. Statistical analyses, including the Wilcoxon rank-sum test, were performed to compare differences between groups. Results: In the subgroup with baseline TP in the lower 50%, the HRS group showed an increase in TP (median ΔTP: 435 ms², interquartile range [IQR]: 964 ms²), while the LRS group showed a decrease (-30.9 ms², IQR: 146 ms²). The between-group difference in TP change was statistically significant (P=0.03). Similarly, low frequency (LF) power increased significantly in the HRS group compared to the LRS group (P=0.03). Although high frequency and very low frequency also showed greater improvement in the HRS group, these changes did not reach statistical significance. Conclusion: RS intake was associated with significant improvements in TP and LF in individuals with lower baseline HRV, suggesting its potential role in autonomic nervous system modulation.