Insulin-sensitizing effects on muscle and adipose tissue after dietary fiber intake in men and women with metabolic syndrome

Context: Dietary fibers have been associated with a reduced incidence of type 2 diabetes mellitus in epidemiological studies; however, the precise mechanisms are unknown. Objective: The objective of the study was to evaluate the efficacy and site of action of an insoluble dietary fiber derived from maize (HAM-RS2) in improving insulin resistance in subjects at increased risk of type 2 diabetes mellitus. Design: This study was a randomized, controlled crossover, dietary intervention study. Setting: The study was conducted at the Centre for Diabetes, Endocrinology, and Research, Royal Surrey County Hospital, Guildford, United Kingdom. Participants: Fifteen men and women with insulin resistance participated in the study. Intervention: The intervention included 40 g/d HAM-RS2 compared with a matched placebo for 8 wk. Main Outcome Measures: After each supplement, participants underwent a two-step hyperinsulinemic-euglycemic clamp study with the addition of glucose tracers; a meal tolerance test; arteriovenous sampling across forearm muscle tissue; and a sc adipose tissue biopsy for assessment of gene expression. Results: There was enhanced uptake of glucose into the forearm muscle measured by arteriovenous sampling (65 ± 15% increase after resistant starch; P < 0.001). Adipose tissue function was also affected, with enhanced fatty acid suppression after HAM-RS2 treatment and an increase in gene expression for hormone sensitive lipase (P = 0.005), perilipin (P = 0.011), lipoprotein lipase (P = 0.014), and adipose triglyceride lipase (P = 0.03) in biopsy samples. There was no effect on the insulin sensitivity of hepatic glucose production or plasma lipids after HAM-RS2. Conclusion: HAM-RS2 improved peripheral but not hepatic insulin resistance and requires further study as an intervention in patients with or at risk for type 2 diabetes.