Fiber and large bowel energy absorption: validation of the integrated ileostomy-fermentation model using pigs

Controversy exists over the contribution of dietary fiber and large bowel fermentation to human energy balance. It has been suggested that large bowel energy absorption, in the form of short-chain fatty acids, can be predicted from in vitro fermentation of human ileal digesta. Because it is difficult to obtain ileal digesta from humans with a functional large bowel to validate this approach, four normal pigs and four pigs fitted with a simple T-cannula at the distal ileum were fed a basal diet supplemented with 0, 5, 10 or 15 g pea fiber per 100 g basal diet in two parallel experiments (Latin-square design). Energy contents of diets, urine, ileal digesta and feces were determined by bomb calorimetry. Apparent total tract energy digestibility did not differ (P > 0.05) between normal and cannulated pigs. Apparent energy digestibility at the ileum decreased with increasing pea fiber intake (P < 0.05). The difference between ileal and fecal gross energy excretions in cannulated pigs was defined as large bowel energy absorption. Aliquots (0.2 g) of freeze-dried ileal digesta were fermented in vitro for 24 h with human fecal inoculum from three donors. In vitro short-chain fatty acid production was correlated with large bowel energy absorption (r = 0.90, P < 0.0001). The metabolizable energy content of pea fiber was determined to be 9.2 kJ/g pea fiber (r = 0.90, P < 0.0001) by regressing metabolizable energy retention against pea fiber intake. The integrated ileostomy-in vitro fermentation model seems to provide accurate estimates of large bowel energy absorption.