The double-blind, randomized, placebo-controlled, parallel-group study, published recently in the journal Nutrition Research , adds to the body of science behind the ingredient.
"In this placebo-controlled study, 4 weeks of ingestion of inulin at a low dose of 2.5 g twice a day was well tolerated and led to a significant increase in faecal bifidobacteria counts in healthy volunteers," wrote lead author Yoram Bouhnik from Paris' Hôpital Lariboisière.
"The results confirm recent in vitro data showing that inulin has a clear prebiotic effect in the Simulator of the Human Intestinal Microbial Ecosystem (SHIME) at a concentration corresponding to a human daily dose of 5 g." Modern recommendations for inulin and oligofructose intake are between five and eight grams per day.
Prebiotic ingredients, or those that boost the growth of beneficial probiotic bacteria in the gut, are worth about €90 million in the European marketplace but are forecast to reach €179.7 million by 2010, according to Frost & Sullivan.
The market has been largely created by three inulin producers, all based in Europe, but other ingredient manufacturers are increasingly looking to promote the prebiotic effect of their products as evidence suggests that prebiotics could be even more useful than the probiotic bacteria that they feed.
The new study recruited 39 healthy adult volunteers (average age 33.9) and assigned them to daily supplements of inulin (2.5g twice a day Fibruline Instant, Cosucra, 20 subjetcs) or placebo (blend of maltodextrin and sucrose, 19 subjects) for four weeks.
The researchers found that, after four weeks of supplementation, the inulin group exhibited a 10-fold increase in Bifidobacteria levels, while no such increases were observed in the placebo group.
Moreover, the increases were sustained in the weeks following the end of inulin supplementation.
"In this study, 2 weeks after stopping the ingestion of bifidus-fermented milk, subjects who consumed inulin-supplemented bifidus-fermented milk had significantly higher fecal bifidobacteria than subjects who ingested unsupplemented bifidus-fermented milk," wrote the researchers.
"These results support the conclusion that inulin is able to sustain a higher level of bifidobacteria for longer periods after its cessation, as we found in the present study."
They also noted a decrease in the concentrations of beta-glucuronidase as a result of inulin supplementation - a result that was again not observed in the placebo group.
"It has been shown that fecal bacterial beta-glucuronidase activity increases in patients on a high-meat diet and that this enzyme could act to increase the amount of substances, such as carcinogens, within the colonic lumen.
This enzyme may play a role in the metabolic activation of procarcinogens and deconjugation processes in the colonic lumen," wrote the researchers.
"Our results corroborate those from studies with probiotics, which have shown that increasing the proportion of the fecal flora represented by bifidobacteria is associated with lower activity of reductive enzymes."
"Under our experimental conditions, this study showed that even at a low dose of 2.5 g twice a day, inulin can exert prebiotic effects such as stimulation of bifidobacteria and decrease in beta-glucuronidase activity, which could be perceived as potentially beneficial for the host," they concluded.
Cosucra has welcomed the study, putting the findings in the context of the newly published European Regulation of Nutrition and Health Claims (Regulation EC 1924/2006).
"It strengthens the scientific background behind the prebiotic claim for chicory inulin," said Cosucra.
Recently, a study from the University of Reading suggested that daily intakes of inulin and oligofructose should err on the high side for maximum gut health benefits.
Their double-blind, placebo-controlled, crossover human study showed that both low and high doses (five and eight grams per day, respectively) boost the population of 'friendly' bifidobacteria in the gut works without side effects.
The Reading study was published in the European Journal of Clinical Nutrition (doi: 10.1038/sj.ejcn.1602636).
Considerable research has already focussed on the role of inulin and oligofructose in bone health and colorectal cancer, and the science is now expanding in ever-increasing circles to cover potential benefits for the immune system, weight management, and intestinal health.
Source: Nutrition Research (Elsevier) Volume 27, Issue 4, Pages 187-193 "Prolonged administration of low-dose inulin stimulates the growth of bifidobacteria in humans"
Authors: Y. Bouhnik, L. Raskine, K. Champion, C. Andrieux, S. Penven, H. Jacobs and G. Simoneau