Breath hydrogen and methane: poor indicators of apparent digestion of soy fiber.

To examine whether end-alveolar breath hydrogen and methane could be used as indicators of fiber digestion in humans, 16 male subjects were fed four fiber-free, complete liquid diets with 0, 30 g (heat processed), 30 g, and 60 g/day soy polysaccharide. Breath hydrogen was measured hourly and breath methane every 4 h on days 6 and 8 of each study period. Feces were collected, homogenized, dried, and analyzed for neutral detergent fiber (NDF). NDF in diets was determined and apparent NDF digestibility calculated. NDF from soy was extensively fermented, greater than 80%, on the fiber-containing diets. No significant relationship was found between breath-gas excretion and fiber digestion, although breath-gas values varied greatly. Breath hydrogen and methane were not significantly different when subjects consumed diets containing 0, 30, or 60 g soy polysaccharide.

Bowel function of healthy men consuming liquid diets with and without dietary fiber.

The importance of the level of dietary fiber intake on bowel function was measured in 16 healthy young males consuming self-selected and liquid enteral diets. Subjects consumed liquid Ensure as their sole nutrient source plus 0 (diet a), 30 (diet c), and 60 (diet d) g/day soy fiber, a fiber source high in hemicellulose that was added to the Ensure. Further, to examine whether heat processing affects the physiologic action of fiber, subjects consumed Enrich, an enteral formula similar to Ensure, which contains 30 g of the same soy fiber (diet b). The four diets were consumed in randomized order each for 10 days. Daily wet stool weight averaged 144.6 g on the self-selected diet and decreased significantly to 67.3 g when Ensure was consumed alone. Average stool weights on diets (b), (c), and (d) were 114.6, 100.2, and 150.3 g/day, respectively. Average fecal dry weights for the four diets were 19.1, 28.7, 25.0, and 30.3 g/day for (a-d), respectively. Gastrointestinal transit time, as measured with radiopaque pellets, was longest on the Ensure diet, 72.4 hr, and approximately 2 days on the fiber-supplemented diets and the self-selected diet. Thus, soy fiber's physiologic effect on laxation was not changed by heat processing. Also, although stool weights were larger on higher fiber intakes, transit rates were similar on all the fiber-containing diets.