Some physical characteristics of dietary fibres and their influence on the microbial ecology of the human colon

Abstract

Current thinking on the subject of dietary fibre tends to emphasize an inclusive definition that overlooks disparate characteristics of individual fibres and their components. The current definition includes all carbohydrate and some non-carbohydrate components that are resistant to mammalian enzymes. The analytical approach proposes to resolve the differences between sources of fibre by characterizing the different proportions of cellulose, hemicellulose, pectin, etc. and in turn resolving these into their respective component sugars. Forage analysis, largely applied to nutrition of ruminants, has emphasized the nutritional non-uniformity of cellulose and hemicellulose despite similarities in chemical linkage and structure of the respective components among different species of forage plants. This has led to the suggestion that intrinsic differences among celluloses are due to macromolecular interactions rather than to their intrinsic structure and composition (Van Soest, I 982). This paper applies the same view to dietary fibre in human nutrition and provides some evidence that physical properties are major determinants of the biological properties of dietary fibre in the human digestive tract. Human feeding study Much of the preliminary information which has emphasized the importance of physicochemical properties of dietary fibre was obtained in a human feeding experiment conducted at Cornell in January-March I 977.. The study included twenty-four young men who were given controlled diets for 80 d. Faeces and urine were collected so that total digestion balances could be obtained. Four sources of fibre were given in the form of prepared breads supplementing a low-fibre basal diet that consisted mainly of meat, eggs and mashed potatoes. Bread on the low-fibre diet was a white bread without any added fibre. The diets were nutritionally adequate for the supply of all known nutrient requirements. All food was taken in a metabolic ward although subjects were free to attend classes and jobs. Each carried toilet collection equipment throughout their daily routine. Dietary intakes were measured and adjusted to maintain body-weight. The test diets included coarse wheat bran and the same bran finely ground, Solka floc (a wood-derived cellulose), cabbage and a low-fibre (white bread) control. Fibre *Human feeding experiment conducted at Cornell in 1977 was supported in part