Cecal Short-chain Fatty Acid Concentrations Research Articles

Prolonged Intake of Fructo-Oligosaccharides Induces a Short-Term Elevation of Lactic Acid-Producing Bacteria and a Persistent Increase in Cecal Butyrate in Rats

While the prebiotic effects of fructo-oligosaccharides (FOS), short-chain polymers of fructose, have been thoroughly described after 2–3 wk of ingestion, effects after intake for several months are unknown. We tested the hypothesis that these effects would differ after ingestion for short and long periods in rats. Rats were fed a basal low-fiber diet (Basal) or the same diet containing 9 g/100 g of FOS for 2, 8 or 27 wk, and cecal contents were collected at the end of each time period. Cecal short-chain fatty acid concentration was higher in rats fed FOS than in those fed Basal, and this effect persisted over time: 83.8 ± 4.1 vs. 62.4 ± 6.5 μmol/g at 2 wk and 103.5 ± 5.8 vs. 73.2 ± 7.4 μmol/g at 27 wk (P < 0.05). The molar butyrate ratio was higher in rats fed FOS regardless of the time period (14.8 ± 0.6% vs. 6.7 ± 1.1% at 27 wk, P < 0.05). Lactate concentration in rats fed FOS was elevated after 2 wk and then decreased: 63.5 ± 21.6 μmol/g at 2 wk vs. 8.8 ± 3.3 μmol/g at 8 wk (P < 0.05). After 2 wk, FOS increased the concentrations of total lactic acid-producing bacteria, and Lactobacillus sp. (P < 0.05), without modifying total anaerobes. However, most of these effects were abolished after 8 and 27 wk of FOS consumption. In the long term, the FOS-induced increase in intestinal lactic acid-producing bacteria was lost, but the butyrogenic properties of FOS were maintained.

The Water-Soluble Extract of Chicory Influences Serum and Liver Lipid Concentrations, Cecal Short-Chain Fatty Acid Concentrations and Fecal Lipid Excretion in Rats

Sprague-Dawley rats (n = 32) were fed diets without fiber (control) or containing 1 or 5% chicory extract or 5% inulin for 4 wk; 0.2% cholesterol was added to all diets. Rats fed chicory extract and inulin diets had significantly higher serum high density lipoprotein (HDL) cholesterol and generally lower low density lipoprotein (LDL) cholesterol concentrations, thus significantly greater ratios of HDL/LDL cholesterol compared with the controls (P < 0.05). The serum apolipoprotein B/apolipoprotein A-1 ratio was significantly lower in rats fed diets containing chicory extract or inulin than that in rats fed fiber-free diets, due to significant reductions in apolipoprotein B concentration (P < 0.05). Greater liver lipid and triglyceride concentrations were observed in rats fed chicory extract or inulin diets compared with the controls (P < 0.05). However, liver phospholipid and cholesterol concentrations were not significantly different among groups (P > 0.05). Addition of 5% inulin to the diet resulted in greater cecal weight, whereas both 5% chicory extract and 5% inulin resulted in greater cecal propionic acid concentration compared with the controls (P < 0.05). Rats fed chicory extract and inulin had significantly greater fecal lipid, cholesterol and bile acid excretions than those fed fiber-free diets (P < 0.05). The results of this study suggest that the improved lipid metabolism observed in rats fed chicory extract (mainly inulin component) may be caused by an alteration in the absorption and/or synthesis of cholesterol, which might result from the changes in cecal fermentation, and by an increase in the fecal excretion of lipid, cholesterol and bile acid.

Varying dietary concentrations of fructooligosaccharides affect apparent absorption and balance of minerals in growing rats

Carbohydrates that bypass digestion in the small intestine and are fermented in the large intestine may affect the absorption of certain minerals. A study was conducted to determine the effect of varying dietary concentrations of fructooligosaccharides (FOS) on the apparent digestibility and balance of certain macro and trace minerals. Forty growing male Sprague-Dawley rats were assigned one of four treatments: 1) purified diet (control); 2) purified diet + 1% FOS; 3) purified diet + 3% FOS, or 4) purified diet + 5% FOS. Rats were acclimated to their metabolic cages for 5 d, after which they were subjected to a 10-d growth period, followed by a 7-d balance period in which diets were restricted to 90% ad libitum intake of the lowest consuming rat. Cecal pH decreased ( P < 0.01) as dietary FOS concentration increased, reflecting an increase in cecal short-chain fatty acid concentration. In addition, FOS supplementation increased ( P < 0.01) fecal N excretion, although N balance was similar among groups. Apparent absorption of Mg increased linearly ( P < 0.01) as FOS concentration increased in the diet; however, Mg balance (mg/d) was similar ( P > 0.10) across treatments. The macrominerals (Ca, P, Mg, Na, Cl, K) and trace minerals (Cu, Fe, Mn, Zn) were in a positive balance for all experimental treatments. However, Cu absorption decreased with increasing FOS concentration. This may be explained by an increase in fecal microbial mass which would contain a relatively significant amount of Cu or by an increase in hepatic bile Cu excretion. These results suggest that dietary FOS alters acute Cu metabolism in growing rats.

The Association of Yogurt Starters with Lactobacillus casei DN 114.001 in Fermented Milk Alters the Composition and Metabolism of Intestinal Microflora in Germ-Free Rats and in Human Flora–Associated Rats

The aim of this study was to compare the effects of milk and of various fermented milks on the composition and metabolic activities of the intestinal microflora. Groups of eight rats were fed for 6 wk a diet containing 30% nonfermented milk (M), yogurt (Y), milk fermented with Lactobacillus casei (LcFM) or milk fermented with the association of L. casei DN 114.001 and yogurt starters (LcYFM). In the first study, the survival of the lactic acid bacteria from the fermented milks was assessed by bacterial enumeration in feces of germ-free rats (GF rats) fed milk or fermented milks. The metabolic activities of the lactic acid bacteria were studied in these rats by the measurement of glycolytic activities and products of bacterial fermentation, i.e., acetate and lactate (isoforms L and D). In a second study, the effects of fermented milks on the composition and metabolism [gas, glycolytic activities, short-chain fatty acids (SCFA), alcohol and ammonia] of human flora were studied using human flora–associated rats (HF rats). In GF rats, the survival of L. casei in the feces did not differ between those fed the LcFM and LcYFM diets. L. bulgaricus was detected in the feces of the rats fed Y, whereas Streptoccus thermophilus was found in the feces of the LcYFM group. In HF rats, fecal concentration of Bifidobacteria was greater in the LcFM group than in the others. β-Glucuronidase (EC 3.2.1.31) activity was lower in rats fed LcFM and Y than in those fed M and LcYFM, whereas β-galactosidase (3.2.1.23), α-glucosidase (EC 3.2.1 20) and β-glucosidase (EC 3.2.1.21) activities were higher in the LcYFM group compared with the others. Methane excretion was higher in rats fed Y than in other groups. Cecal SCFA concentrations did not differ in LcFM, Y and M groups, but total SCFA, acetate, propionate and butyrate were significantly greater in the LcYFM group. These results suggest that milk fermented with the combination of L. casei and yogurt starters leads to specific effects that are different from the simple addition of the effects found with yogurt and milk fermented with L. casei. These specific effects are potentially beneficial to human health.

Effects of Soybean Pectic Polysaccharide on Cholesterol Levels in Rats.

The effects of soybean pectic polysaccharide on cholesterol metabolism in rats were examined. The polysaccharide gradually repressed the increase in the serum cholesterol level; whereas, citrus pectin rapidly repressed the increase and cholesterol accumulation in the liver was not observed. Significanct differences in cecal short-chain fatty acid concentrations were not observed; therefore, further experiments are necessary to clarify the mechanism.