Formation, pattern and physiological effects of short-chain fatty acids - Impact of various indigestible

The short-chain fatty acids (SCFA) formed from colonic fermentation of indigestible carbohydrates have been suggested to exert different physiological effects. In this thesis the fermentability and SCFA produced from various indigestible carbohydrates in the hind-gut were investigated using balance experiments in rats. In the case of propionate, experiments were also performed to evaluate possible metabolic effects. The quantity of material fermented in the hind-gut correlated well with the total amount of SCFA produced in caecum. However, the caecal distribution of the individual SCFA: acetic, propionic, and butyric acid varied between the different materials tested. ß-glucans and raffinose produced high proportions of butyric acid (15%), whereas guargum gave high proportions of propionic acid (27%). Mixtures of indigestible carbohydrates gave higher proportions of butyric acid (19%) than all the individual substrates tested. Fermentation of resistant starch produced intermediate caecal proportions of propionic (about 16%) and butyric acid (9%). To increase the amount of starch fermented in the hind-gut, an -glucosidase inhibitor, Acarbose, was added at two levels to a starch based diet containing a mixed source of dietary fibres. The caecal SCFA pool was almost doubled but without a change in distribution of butyric acid (18%). However, with the Acarbose supplemented diets, the concentration of propionic acid increased in colonic contents, and in distal colon butyric acid concentration increased at the higher level of Acarbose. When probiotics (Lactobacillus reuteri R2LC and/or Lactobacillus plantarum DSM9843) were added to a mixed diet based on oat-meal, SCFA pools and distributions were unaffected in comparison with a diet without probiotics. Antibiotic treatment resulted in significantly lower concentrations of SCFA twelve days after ceased treatment, as well as an alteration in the SCFA pattern. The distribution of butyric acid in caecum decreased from 17% to 4%, whereas the amount of succinic acid increased from 0 to 25%. The amount of succinic acid decreased along the hind-gut to be only 2% in faeces, whereas that of butyric acid remained low. The effect of sodium propionate on cholesterol and glucose metabolism was investigated using obese hyperinsulinaemic rats. Inclusion of sodium propionate to a diet high in saturated fat and cholesterol reduced both fasting blood glucose levels and glucose excretion in urine in comparison to rats fed a diet without propionate. In addition, total pool of cholesterol in the liver decreased. When propionate was infused rectally to the large bowel only the liver cholesterol levels were reduced. However, this effect was achieved with a significantly lower dosage.