Dietary carbohydrates affect caecal fermentation and modify nitrogen excretion patterns in rats - I. Studies with protein-free diets

In a two-factorial experiment on 96 young male rats, the effects of substit uting 10% raw potato starch (PS), pectins (PEC), or cellulose (CEL) for cor n starch (CS) were studied using an unsupplemented protein-free (PF) diet o r a PF diet supplemented either with DL-methionine or urea. The pH and the short chain fatty acids (SCFA) content in caecal digesta, as well as caecal digesta and tissue weights were determined and used as the criteria of cae cal fermentation intensity. Blood urea level, amount of N excreted via faec es and urine, DAPA content, and amino acid composition of faecal protein we re analyzed as indices of protein metabolism. A 10-day adaptation period to the carbohydrates fed with the casein diet pr eceded the experimental period of feeding the respective carbohydrates with protein-free diets. Dietary carbohydrates significantly influenced total and individual SCFA co ntent in caecal digesta, as well as other parameters related to the intensi ty of fermentation. Potato starch and pectins were more intensively ferment ed than cellulose. Supplementation of the PF diet with methionine and urea affected only caecal isobutyric and valeric acid content in a way dependent on the carbohydrates present in the diet. Carbohydrates significantly altered the routes of N excretion. Faecal excre tion was increased by ail carbohydrates studied compared to corn starch, pe ctins had the most marked effect. Urinary excretion was significantly incre ased by cellulose las compared with the PEC and PS groups) and decreased by pectins as compared with all other groups. There was an interaction between the effects of carbohydrates and type of p rotein-free diet on faecal and urinary excretion. The sum of amino acids in faecal protein was the lowest on the PEC diet, but the amino acid composit ion expressed as a per cent of total amino acid content was similar in all groups. It can be concluded that dietary carbohydrates alter the excretion patterns of endogenous nitrogen in rats in different ways and that this eff ect is related to the intensity of their fermentation in the hind gut.