Inulin measured as fructose in faeces of rats fed sucrose-based diets is not confounded by the presence of fructose derived from sucrose

Abstract

This study aimed to determine whether measurements of faecal inulin as fructose in the faeces of rats fed inulin in sucrose-based diets are confounded by fructose derived from sucrose. Sprague-Dawley rats were fed diets containing 58.5% sucrose supplemented with 5% cellulose (control) or 5% inulin for 7 or 14 days. Fructose or fructose polymer in the faeces was extracted with hot 0.1M hydrochloric acid and measured with a specific colourimetric method. Nearly all (99.8%) of the fructose fed as sucrose in cellulose-supplemented diets did not appear in the faeces. In rats fed 5% inulin, about 98.5% of the total dietary fructose was utilised, and approximately 1.5% appeared in faeces. By subtracting apparent sucrose-derived fructose in the cellulose control diets from total fructose in the faeces from inulin-fed animals, faecal fructose was calculated to be about 10% of the inulin that had been consumed. A small proportion of inulin fed to rats at a level of 5% in the diet may survive caecal fermentation and appear in the faeces. This faecal inulin may be measured without interference from sucrose-derived fructose when fed in starch-free diets using sucrose as the sole source of digestible carbohydrate.