EFFECTS OF NATURE, SIZE AND LEVEL OF INCORPORATION OF DIETARY-FIBERS ON COLONIC FUNCTIONS IN GERM-FREE RATS AND IN HETEROXENIC RATS INOCULATED WITH A HUMAN FLORA

Dietary fibres are degraded by the digestive microflora. Our study aimed to dissociate the role played by the flora from that played by the fibres in the physiological properties commonly attributed to fibre. Using germ-free and heteroxenic rats inoculated with a human flora from a methane producer, we investigated first the effects of the digestive microflora and of the botanical origin of fibres on water intake and excretion, and the possible relationships between transit time and fermentation gas excretion. Dietary fibres differed qualitatively (wheat bran, carrot fibre and beet fibre) and quantitatively (10% of coarse wheat bran, carrot fibre, 10 or 20% of fine and coarse beet fibres). They were incorporated in a human-type diet. We compared water intake, faecal water excretion and transit time, and we measured the total hydrogen and methane excretion of heteroxenic mts placed in a respiratory chamber connected to isolators. In germ-free beet rats beet fibre shortened transit time, increased water intake and faecal water excretion. Transit time was inversely related to dietary fibre intake, water excretion and stool output. In heteroxenic mts, water intake remained the same with wheat bran while it decreased with beet fibre. Faecal water excretion was the same with both fibres. Transit time was no longer related to the other parameters (dietary fibre intake, outputs). The concentration of fermentation gases were seven times higher with beet and carrot fibre than with wheat bran. Hydrogen excretion remained low, whereas that of methane changed with the type of dietary fibre intake, the concentration of dietary fibres in the diet and the particle size. The proportion of methane was higher with beet fibre than with carrot fibre. We conclude that the digestive microflora regulate transit time; indeed, they decreased transit time which was initially long (10% dietary fibre in the diet), while they increased transit time which was initially short (20% dietary fibre in the diet). Secondly, the botanical origin of the fibres influenced the type and concentration of fermentation gases. Finally, transit time and fermentation gas were related at a high fermentation level: a high fermentation gas excretion was associated to a longer transit time.