Prolonged administration of low-dose inulin stimulates the growth of bifidobacteria in humans

The effect of low-dose inulin consumption on fecal bifidobacteria growth, microbial activity, and tolerance in healthy adults was investigated in a double-blind, randomized, placebo-controlled, parallel-group study. Thirty-nine healthy volunteers were randomly assigned to 2 groups and ingested 2.5 g inulin or placebo twice a day for 4 weeks (from week 2 to week 6). Fresh stools were collected after 2, 4, 6, and 8 weeks for fecal bacteria count and fecal bacterial enzymatic activity measurement. Tolerance was evaluated from a daily chart. In the inulin group, fecal bifidobacteria count increased (P < .0001), whereas no change was observed in the placebo group. Lactobacillus counts did not change in the inulin group and decreased in the placebo group (P = .0004). In the inulin group, a decrease in β-glucuronidase activity (P = .001) was found, which was negatively correlated with the level of Bifidobacterium (P = .04). Throughout the study, there was no change in fecal enterobacteria, pH, β-galactosidase activity, reductase activity, or short-chain fatty acid level in either of the groups. Excess flatus significantly increased in both groups (inulin, P < .0001; placebo, P = .03), but its intensity was very mild. Even at doses as low as 2.5 g twice a day, inulin can exert a prebiotic effect in healthy volunteers by stimulating bifidobacteria growth.