Dietary fiber supplementation may improve gastrointestinal tolerance and decrease diarrhea in patients receiving enteral formula diets. To compare the effects of two dietary fibers on bowel function parameters and short-chain fatty acid excretion we fed 11 healthy men three defined enteral formula diets in random order for 18 days each. The test diets consisted of a fiber-free formula and daily intakes of maltodextrin (0 g of fiber), 15 g of total dietary fiber as an enzymatically modified guar gum, and 15 g of total dietary fiber as soy polysaccharide. Data were also collected while subjects consumed self-selected diets for 5 days. Mean transit time was longer and fecal moisture content was lower on 0 g of fiber and modified guar than on the self-selected and soy diets. Furthermore, mean transit time was slightly longer and fecal nitrogen excretion greater on modified guar compared with 0 g of fiber. Daily fecal output and frequency of defecation were greater, fecal pH was lower, and fecal butyrate concentrations were higher on the self-selected diet compared with the enteral formula diets. However, there was no difference in these parameters among the three liquid diets. Thus, despite significant differences in mean transit time, few differences in other parameters of bowel function were observed when healthy subjects consumed enteral formula diets containing 0 g of fiber and 15 g of total dietary fiber as modified guar and soy.