Colonic fermentation of some breads and its implication for energy availability in man

Abstract

Five breads (100% wholemeal wheat (Wheat), 75% bulgar: 25% wheat flour (Bulg1), 50% bulgar: 50% wheat flour (Bulg2), 100% rye (Rye), and 100% pumpernickel (Pump)) were substituted isocalorically for white bread (White) and fed to a healthy ileostomate for three days and the ileal effluent was collected and analysed. Small intestinal apparent metabolizable energy (ME a) absorption, determined using the Atwater energy system [(crude protein×4.0 Kcal/g)+(extractable fat×9.0 Kcal/g)+(total carbohydrate×4.0 Kcal/g)], decreased for the five breads from 92.7% for white to 88.2% for Pump. The collected ileal effluent was then fermented in vitro with mixed human microflora for 24h and short chain fatty acid (SCFA) production was measured (mmol SCFA/g ileal organic matter) and the available energy (AE) potentially absorbed as SCFA was predicted. It was estimated that the whole grain breads would increase the number of calories being absorbed as SCFA by 20% to 70% relative to white bread. The net metabolizable energy (NME), the sum of ME a and the AE, available to an individual with an intact colon was estimated to be 96% of the caloric intake determined using the Atwater energy system. However, there was a dramatic shift in energy absorption from the small intestine to the colon with 3.7% of the NME being absorbed as SCFA when white bread was consumed versus 6.3% from pumpernickel.