Physiological effects of inulin in germ-free rats and in heteroxenic rats inoculated with a human flora

The purpose of this investigation was to study the effects of inulin on physiological and nutritional parameters and on intestinal fermentation. Blood parameters (glucose, cholesterol and triglycerides) and nutritional parameters were compared in germ-free rats and in rats associated either with human flora from a methane producer or with human flora from a non-methane producer. In heteroxenic rats, total hydrogen and methane excretions were measured in a respiratory chamber and other bacterial metabolites (SCFA, and L- and D-Iactic acids) were determined in the caecum. Rats were fed a 'human-like' diet containing either 10% sucrose (control diet) or 10% inulin (inulin diet). In control groups, faecal excretion was higher and dry matter digestibility was lower in germ-free rats than in heteroxenic rats. Non-methane producers differed from methane producers by their fermentation products: caecal SCFA concentration was lower and lactic acid concentration was higher in methane producers. Inulin ingestion did not modify nutritional and blood parameters of germ-free rats. In heteroxenic rats it did not modify blood glucose and blood cholesterol but it increased triglycerides. In non-methane producers, hydrogen production was enhanced and SCFA concentration did not change, but the proportion of butyrate and the concentration of lactic acid increased, whereas the LiD lactic acid ratio decreased. In methane producers hydrogen production was enhanced and methane production fell; caecal lactic acids, SCFA concentration, and the proportion of butyrate increased. Inulin tends to reduce the differences between the metabolism of methane- and non-methane-producing floras and tends to convert methane producers into non-methane producers.