INFLUENCE OF 3 DIFFERENT FIBER-SUPPLEMENTED ENTERAL DIETS ON BOWEL FUNCTION AND SHORT-CHAIN FATTY-ACID PRODUCTION

Background: Dietary fiber is known to influence bowel habit and gastro intestinal mucosal cell morphology and function. Large-bowel function is particularly influenced by insoluble, poorly fermentable fiber sour ces, whereas mucosal function is affected by fiber sources that are so luble and highly fermentable. The aim of the present study was to comp are bowel function during consumption of a self-selected diet, a fiber -free enteral diet, and three polymeric enteral diets, each supplement ed with a fiber with different fermentation characteristics. The fiber sources used were oat, soy oligosaccharide, and soy polysaccharide. M ethods: Seven healthy subjects consumed four diets in random order for 4 to 7 days. These were a self-selected diet, a 2-L polymeric enteral diet, and a 2-L polymeric enteral diet supplemented with 15 g of tota l dietary fiber per liter derived from either soy oligosaccharide fibe r (75 g/L) or oat fiber (15 g/L). An additional six healthy subjects w ere randomly assigned to three diets (4 to 7 days): a self-selected di et, a 2-L polymeric enteral diet, or the same 2-L polymeric enteral di et supplemented with 20 g of soy polysaccharide fiber per liter (15 g of total dietary fiber per liter). Bowel function was assessed by meas uring whole-gut transit time, mean daily stool wet weights, and bowel movement frequency per day. Fermentation characteristics of the differ ent fiber sources were determined quantitatively and qualitatively by measuring short-chain fatty acids produced during in vitro stool cultu re. Results: Total short-chain fatty acid and butyric acid production with soy oligosaccharide fiber were significantly higher compared with values observed for soy polysaccharide fiber (p < .003), oat fiber (p < .005), and self-selected (control) diet (p < .003). Compared with t he fiber-free diet, consumption of the soy polysaccharide, oat, and so y oligosaccharide-fiber-supplemented enteral diets did not significant ly (p > .05) alter whole-gut transit time or stool wet weight. However , bowel frequency was significantly improved by consumption of the soy polysaccharide-fiber-supplemented diet but not the oat fiber or soy o ligosaccharide-fiber-supplemented diets. Conclusion: Compared with a f iber-free polymeric enteral diet, the daily consumption of an enteral diet supplemented with 30 g of total dietary fiber per day derived fro m a poorly fermentable oat fiber, a highly fermentable soy oligosaccha ride fiber, or a moderately fermentable soy polysaccharide fiber has l ittle impact, if any, on bowel function.