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.