Health Effects of Dietary Fermentable Fiber (Resistant Starch)

Resistant starch (RS) reaches the large intestine for fermentation and is considered a prebiotic. We wanted to determine if we could reduce fermentation for future mechanistic studies and how there is improved insulin sensitivity in human studies with or without increased incretin hormone glucagon-like peptide 1 (GLP-1). Two main studies were performed. In the first main study, low potency antibiotics (Ampicillin 1g/L and Neomycin 0.5g/L) were added to the drinking water of rats to reduce fermentation of RS. Antibiotics were used either prior (first) to or during (second) feeding of RS. Results demonstrated that low potency antibiotics given prior to resistant starch feeding were not able to prevent fermentation in the cecum independently of water or cecal contents gavage (donor rats fed resistant starch). Low potency antibiotics given during resistant starch feeding were able to reduce fermentation. The main purpose of second main study was to determine if resistant starch, as either an isolated starch or in a whole grain flour, increases gene expression of pyruvate carboxylase (PCase), and glucose-6-phosphatase (G6Pase). These two enzymes are involved in intestinal gluconeogenesis (IGN) which improves endogenous glucose control. Certain diets can trigger IGN. Goto-Kakizaki (GK) rats (first) and Sprague Dawley rats (second) were used to measure IGN gene expression in the fasted or fed state, respectively. GK rats were in four diet groups, two control diets (highly digestible isolated starch, CON; and low resistant starch whole grain flour, WG) and two high resistant starch diets (high amount of isolated resistant starch, RS; high amounts of resistant starch in a whole grain flour, WG+RS). Gene expression was measured in the fasted state with insulin injection used to model fed state. Sprague Dawley rats were fed the same diets but with moderate or high fat and gene expression measured in the fed state. High resistant starch in the diet increased IGN gene expression in the fed state, regardless of fat level. In the fasted state, there were no significant increases of PCase or G6Pase even with insulin injection. Improvement of insulin sensitivity regardless of GLP-1 production in humans fed resistant starch may be a result of IGN