Substrate for fermentation in man

Abstract

A variety of different substrates are excreted from the small bowel as possible substrates for bacterial fermentation in the large bowel. Ileostomy studies have shown that 50-90 g/d of dry weight (800-1700 kJ/d) is excreted from the small bowel. Although the amount of non-starch polysaccharides (NSP), the main component of dietary fibre in the diet, causes considerable changes in excretion patterns, NSP is not the dominant part of the energy excreted to the large bowel. Resistant starch in common Western diets amounts to 34% of the starch intake, if the diet is not high in e.g. beans. Oligosaccharides, sugars and fat contribute only a few grams each, whereas the excretion of protein can be estimated to 10-15 g/d. Calculation of substrate and energy shows that a considerable amount of energy, equivalent to 15-40 g of carbohydrate, is metabolised in the large bowel. Keywords: Bacteria, colon, energy, fermentation, nutrients