Effects of Resistant Starch on Metabolic Markers and Gut Microbiota in Women with Metabolic Syndrome Risk Factors: A Randomized, Double-Blind, Pilot Study

Background/Objectives: Resistant starch intake has been shown to influence gut microbiota composition and affect metabolic markers. These effects may be partially attributed to enhanced short-chain fatty acid (SCFA)-mediated energy harvesting and hepatic lipogenesis induced by resistant starch fermentation. However, there is a lack of prospective research addressing these associations. To address this gap, we performed a double-blind, randomized dietary intervention study to investigate the impact of high versus low resistant starch consumption on metabolic markers and gut microbiota among adult women presenting with risk factors for metabolic syndrome. Methods: A total of 30 participants were randomly assigned to either the low-resistant starch (LRS) or high-resistant starch (HRS) diet groups. Each group, comprising 15 participants, consumed one food product per day enriched with either high or low resistant starch for 8 weeks. Changes in metabolic indices and gut microbiota were assessed and compared with baseline values, as assessed before diet (Week 0). Results: After 8 weeks of intervention, the HRS diet significantly increased body weight, body fat, and triglyceride (TG) level (mean change ≈ +40 mg/dL), while reducing blood pressure. Analysis of intestinal microbiota in the HRS group revealed a statistically significant increase in the genus Veillonella following the intervention. Conversely, the genus Marvinbryantia increased significantly in the LRS group. Conclusions: In women with metabolic risk factors, resistant starch supplementation elicited mixed metabolic responses—showing a modest reduction in blood pressure but concurrent increases in adiposity and TG concentrations. As the TG elevation reached a clinically meaningful magnitude, dietary interventions involving high-resistant starch should incorporate regular lipid monitoring to ensure cardiometabolic safety. Collectively, these findings highlight the complex interplay between SCFA-producing gut microbiota and host energy metabolism, suggesting that individualized dietary strategies may be required to optimize metabolic outcomes.