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close this bookActivity, Energy Expenditure and Energy Requirements of Infants and Children (International Dietary Energy Consultative Group - IDECG, 1989, 412 pages)
close this folderThe energy requirements of growth and catch-up growth
close this folder8. Extent to which colonic fermentation of carbohydrates contributes to energy requirements in childhood
View the document8.1. Colonic fermentation
View the document8.2. Energy from SCFA
View the document8.3. Factors influencing SCFA production
View the document8.4. Gross versus metabolizable energy
View the document8.5. Faecal energy and non-starch polysaccharide
View the document8.6. Faecal energy in cystic fibrosis

8.1. Colonic fermentation

During the past decade there has been an increased interest in the effects of dietary fibre on human metabolism and physiology. It is now widely appreciated that substantial fermentation of dietary carbohydrate takes place in the large intestine, but the contribution made by fermentation to the energy economy of the body is less clear. Fermentation is an important component of normal large-bowel activity (CUMMINGS and ENGLYST, 1987). It is the process whereby anaerobic bacteria (and yeasts) break down dietary and other substrates, principally carbohydrate, to obtain energy for growth and the maintenance of cellular function. A variety of potentially fermentable substrates may enter the large intestine. These include dietary fibre (non-starch polysaccharide, NSP), unabsorbed dietary residue (starches and sugars) and endogenous secretions and cellular debris (intestinal glycoproteins and mucopolysaccharides). The relative proportions of each of the substrates will vary with dietary intake, the extent of maldigestion or malabsorption and mucus production within the gut. The end-products of anaerobic carbohydrate breakdown are short-chain fatty acids (SCFA: acetic, proprionic and butyric acids), gases (hydrogen, carbon dioxide and methane) and energy. The energy is used by the intestinal microflora for growth, whereas most of the SCFA are absorbed through the colonic mucosa and may contribute to the host's energy supply. The output of SCFA in faeces is minimal (RUBENSTEIN, HOWARD and WRONG, 1969). The absorption of SCFA stimulates sodium and water absorption, thereby being an important contributor to salt and water homeostasis in the colon. The production of SCFA may be of importance in maintaining the health of the epithelium of the large bowel. The epithelial cells of the colon metabolize SCFA, especially butyrate, which is their preferred fuel (ROEDIGER, 1980). Following absorption, SCFA pass into the portal vein and thence to the liver where proprionate and some acetate are taken up. The remaining acetate may pass on to peripheral tissues, being metabolized by muscle.