Prolonged intake of fructo-oligosaccharides induces a short-term elevationof lactic acid-producing bacteria and a persistent increase in cecal butyrate in rats

While the prebiotic effects of fructo-oligosaccharides (FOS), short-chain p olymers of fructose, have been thoroughly described after 2-3 wk of ingesti on, effects after intake for several months are unknown. We tested the hypo thesis that these effects would differ after ingestion for short and long p eriods in rats. Rats were fed a basal low-fiber diet (Basal) or the same di et containing 9 g/100 g of FOS for 2, 8 or 27 wk, and cecal contents were c ollected at the end of each time period. Cecal short-chain fatty acid conce ntration was higher in rats fed FOS than in those fed Basal, and this effec t persisted over time: 83.8 +/- 4.1 vs. 62.4 +/- 6.5 mu mol/g at 2 wk and 1 03.5 +/- 5.8 vs. 73.2 +/- 7.4 mu mol/g at 27 wk (P < 0.05). The molar butyr ate 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 mu mol/g at 2 wk vs. 8.8 +/- 3.3 mu mol/g at 8 wk (P < 0.05). After 2 wk, FOS increa sed the concentrations of total lactic acid-producing bacteria, and Lactoba cillus 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 l ong term, the FOS-induced increase in intestinal lactic acid-producing bact eria was lost, but the butyrogenic properties of FOS were maintained.