Composition of faeces from human subjects consuming diets based on conventional foods containing different kinds and amounts of dietary fibre

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Abstract
The stool-bulking effect of dietary fibre (DF) is well-documented and believed to be important in the postulated beneficial effect of DF on human health. The aim of the present study was to investigate the digestibility of DF in relation to its stool-bulking properties and to study possible mechanisms for this effect. Four diets, based on conventional foods only, were studied in balance experiments on human subjects. Diet A contained DF mainly from whole-grain cereals while diets B1 and B2 contained DF mainly from pulses, vegetables and fruit. Diet C was a low-fibre diet. Faeces was fractionated into four fractions, each enriched in one of the following three components: undigested DF (fractions 1 + 2), faecal bacteria (fraction 3) and soluble components (fraction 4). The digestibility of DF in diets A, B1 and B2 was 0.62, 0.88 and 0.90 respectively. Subjects consuming diet A excreted slightly more fraction 3 than subjects consuming the other diets. Thus, the statement that DF of high digestibility stimulates microbial growth in the gut was not supported. The water-holding capacity of fraction 1 was studied in vitro and was found to be low. It is suggested that undigested soluble DF is important in the stool-bulking properties of DF.