APPARENT FIBER DIGESTIBILITY AND FECAL SHORT-CHAIN FATTY-ACID CONCENTRATIONS WITH INGESTION OF 2 TYPES OF DIETARY FIBER

Short-chain fatty acids (SCFAs) are products of dietary fiber fermenta tion. As such, fiber digestibility is thought to be related to SCFA pr oduction. The effects of two concentrations of cereal fiber as wheat, bran (WB) and vegetable fiber (VF) on fiber digestibility were examine d in 34 free-living volunteers. Five diets consisting of a fiber-free liquid mutation supplement and quick breads containing either (1) 0 g of fiber, (2) 10 g of WB, (3) 30 g of WB, (4) 10 g of VF, or (5) 30 g of VF were consumed in random order. Apparent digestibility of neutral detergent fiber (NDF) was determined. Colonic fluid, collected by in vivo dialysis in 9 subjects, was analyzed for SCFAs by gas chromatogra phy. Digestibility of NDF was greater with WB than with VF ingestion i n those 9 subjects, but digestibility was not different with ingestion of both fibers when all 34 subjects were considered. No effect of int ake level was seen with either WB or VF. Fiber ingestion increased ace tate, propionate, and butyrate concentrations above those on the 0 g o f fiber diet (43%, 31%, and 90%, respectively; p < .0001). Propionate and butyrate concentrations were greater on WB than VF (p < .01); acet ate concentrations were similar with both fibers. No correlation betwe en NDF digestibility and SCFA concentrations was observed. Despite dif ferences in origin, chemistry, particle size, and subject transit time , the WB and VF were similar in NDF fermentability. Molar ratios of sp ecific SCFAs were influenced by type of fiber ingested.