(Journal of Nutrition. 1999;129:1442S-1445S.)
© 1999 The American Society for Nutritional Sciences
Supplement
Dose-Response Effects of Inulin and Oligofructose on Intestinal Bifidogenesis Effects1
A. V. Rao
Department of Nutritional Sciences, Faculty of Medicine, University of Toronto, Toronto, Ontario, Canada
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ABSTRACT
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Recent studies have identified several beneficial attributes of inulin
(I) and oligofructose (OF) in human health. However, most of the
studies pertaining to the physiologic role of these compounds have been
conducted at higher concentrations (8–40 g/d) as a source of dietary
fiber. There is growing interest in using I and OF as a substrate for
the selective growth of beneficial gastrointestinal bacteria such as
the bifidobacteria. In vitro fermentation studies using fecal inoculums
have shown that I and OF are utilized rapidly and completely by
intestinal microflora and that the degree of polymerization of the
substrate influenced its rate of disappearance. In these and other
studies, I and OF were shown to be efficient substrates for the growth
of most strains of bifidobacteria compared with glucose. In vivo
studies have also shown that when human volunteers ingested I or OF,
the number of fecal bifidobacteria increased. However, when results
from the reported studies are combined and analyzed, a
dose-response relationship in terms of log increases in the count
of bifidobacteria cannot be demonstrated. Initial numbers of
bifidobacteria in the feces, independent of the dose of the
fructo-oligosaccharides, seem to influence the results. Future
investigations should consider this relationship carefully.
KEY WORDS: • prebiotics • bifidobacteria • intestinal microflora • oligofructose • chicory oligofructose
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INTRODUCTION
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The intestinal microbial flora of humans represent a rich ecosystem
composed of a wide range of metabolically active microorganisms that
play an important role in influencing the health of the host. Of the
several hundred species of bacteria that colonize the large intestine,
bifidobacteria are generally considered to be health promoting and
beneficial. Predominance of bifidobacteria is now recognized as being
essential for the prevention of diseases and maintaining good health
(Mitsuoka 1990
). Accordingly, considerable research is
being directed at promoting the growth of bifidobacteria in the large
intestine. One main strategy being employed is the use of selective
carbohydrate substrates for the growth of indigenous bifidobacteria,
the "prebiotic" approach (Gibson and Roberfroid 1995
). To be effective, these carbohydrates must reach the
colon undigested and unabsorbed in the upper gastrointestinal tract and
be selectively utilized by the resident bifidobacteria. Inulin type
fructans are examples of such carbohydrates. They consist of 2–60
fructose units linked by a ß-(2
1)-glycosidic linkage often with a
terminal glucose unit (Clevenger et al. 1988
,
Roberfroid et al. 1998
). These fructans are not
hydrolyzed by the digestive enzymes in the small intestine; they reach
the colon unabsorbed and are utilized selectively as a substrate for
the growth of bifidobacteria. They are present in many widely consumed
fruits and vegetables. Commonly, they are either synthesized from
sucrose through the action of fungal-fructofuranosidase
(SF)2or extracted from chicory root in the form of inulin (I) and
enzymatically hydrolyzed under controlled conditions to oligofructose
(OF). Several dietary intervention studies have been conducted in
humans using fructans; these have been reviewed recently by
Roberfroid et al. (1998).
Collectively, there is
convincing evidence to indicate that inulin-type fructans
selectively stimulate the growth of bifidobacteria both in vitro and in
vivo.
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In vitro fermentation of inulin and oligofructose
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The growth rates (per hour) of various pure cultures of
bifidobacteria grown on either inulin, oligofructose or glucose were
compared (Wang 1993
). Results indicated that all strains
of bifidobacteria tested grew better on chicory oligofructose than on
glucose. Chicory inulin gave higher growth rates in the case of
Bifidobacterium infantis, B. pseudo-longum, B. angulatum and
B. breve (Fig.
1).In another study, human fecal slurries were incubated in batch
anaerobic cultures (Wang and Gibson 1993
) in the
presence of 7 g/L fructose, starch, inulin or oligofructose. At the end
of 12 h, both inulin and oligofructose showed significant
increases in the number of bifidobacteria (Fig. 2
).Chicory fructans were also shown to selectively stimulate the growth of
bifidobacteria when continuous chemostat cultures were inoculated with
160 g/L fecal slurry (Gibson and Wang 1994
). Glucose, on
the other hand, failed to stimulate the growth of these bacteria. In
another recent study, Reading et al. (1998)
undertook an
in vitro study to investigate the minimum level of oligofructose
required to obtain significant growth stimulation of bifidobacteria.
They tested five oligofructose doses, equivalent to daily doses of 1,
2, 4, 6 and 8 g, using 50-mL batch culture fermentations. Fecal
samples obtained from six healthy human subjects were homogenized and
used after dilution to inoculate the batch cultures. Microbial
populations present in each batch culture after 0, 6 and 24 h of
anaerobic incubation at 37°C were enumerated. Results indicated a
bifidogenic effect at all oligofructose dosages tested. Although the
number of bifidobacteria increased even at a dosage of 1 g/d equivalent
of oligofructose, other bacteria including Bacteroides, coliforms and
gram-positive cocci also grew well at this dose. However, an
oligofructose dosage equivalent to 2 g/d increased bifidobacterial
numbers more selectively. The biofidogenic effect of oligofructose was
optimized at the 4 g/d
level.
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Figure 2. Effect of different sugars on the in-vitro growth of human fecal
bacteria (Wang and Gibson 1993).
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In vivo fermentation of inulin and oligofructose
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Most of the studies pertaining to the physiologic role of fructans
in human health have been conducted at higher concentrations as a
source of dietary fiber. Hidaka et al. (1986)
studied
the effect of administering 8 g of oligofructose (Neosugar) per
day in the form of a drink or jelly to humans for a period of 2 wk and
found a 10-fold average increase in bifidobacteria colony counts and a
significant decrease in Clostridium perfringens (pathogenic
bacteria) count. Oligofructose had also normalized the stool
consistency in subjects who had moderate/severe constipation or
diarrhea. In another study (Hidaka et al. 1991
),
hyperlipidemic out-patients were randomly divided into either a
placebo group (8 g/d sucrose) or an oligofructose group (8 g/d
oligofructose) and maintained on their respective treatment for a
period of 5 wk. Fecal bifidobacteria in those receiving oligofructose
were significantly greater compared with those given sucrose. From an
initial 9.8% of the total fecal flora, bifidobacteria accounted for
50.1% by the end of 5 wk. A simultaneous reduction in
Bacteroidaceae and Eubacterium was also observed
in this study (Fig. 3
). (Williams et al. (1993
) showed a significant increase in bifidobacteria with 4
g/d of oligofructose ingestion by healthy human subjects. Both chicory
inulin and oligofructose when added as supplements to strictly
controlled diets at the rate of 15 g/d for 15 d produced
significant modifications in the composition of the fecal microflora
(Gibson et al. 1995
). The most striking effect was an
increase in the number of bifidobacteria of equal magnitude for both
fructan products. In this study, a significant reduction in
bacteroides, fusobacteria and clostridia was also observed
(Fig. 4
and Fig. 5
).Ingesting the chicory fructans resulted in a major shift toward fecal
bifidobacteria that became numerically the most predominant bacterial
group. Kleessen et al. (1997)
fed inulin to constipated
elderly subjects and demonstrated a significant increase in the
bifidobacteria count in the feces by more than one log cycle, at the
same time improving their constipation. Bouhnik et al. (1996)
compared the effect on fecal bifidobacteria of prolonged
ingestion of Bifidobacteria sp. fermented milk (BFM) with or without
the addition of inulin at the rate of 18 g/d. They observed that the
ingestion of BFM itself, without the addition of inulin, significantly
increased fecal bifidobacteria (Fig. 6
). As a result, no further increase was shown with the addition of
inulin. However, in this study, 2 wk after stopping the ingestion of
BFM products, subjects who consumed inulin-supplemented BFM had
significantly higher fecal bifidobacteria compared with subjects
ingesting BFM that was not supplemented with inulin. These results did
support the conclusion that inulin was able to sustain a higher level
of bifidobacteria for longer periods of time. More recently,
Menne et al. (1997)
studied the effect of feeding
Fm-type oligofructose on fecal bifidobacteria. After a
run-in period of 2 wk of consuming a controlled diet, eight healthy
volunteers were administered a supplemented controlled diet for 2 wk
followed by 3 wk of a supplement-free diet. Both diets were
supplemented with 8 g/d of chicory oligofructose. At the end of the two
feeding periods, a significant increase in the fecal bifidobacteria
counts compared with the placebo period was observed. In this study, a
concomitant reduction in Bacteroides spp. was also observed. In a
recent article, Roberfroid et al. (1998)
summarized the
published data showing an in vivo increase in the counts of
bifidobacteria in human feces after consumption of various doses of
oligofructose added to the usual diet (Table 1
).The dose of oligofructose ranged from 4 to 20 g/d. In all cases,
significant increases in fecal bifidobacteria at the end of the trial
were reported. However, as the author notes, levels of other fecal
bacteria were not always reported in these studies.
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Figure 6. Effect of inulin on bifidobacterium fermented milk (BFM) induced fecal
bifidobacteria (Bouhnik et al. 1996).
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Table 1. In Vitro Effects of Fructans on the Composition of Human Fecal
Microflora (Wange 1993, Gibson and Wang 1994, Roberfroid et al.
1998)
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Dose-effect relationship between inulin-type fructans and human
fecal bifidobacteria
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Published results from various human feeding studies clearly
demonstrate the bifidogenic nature of inulin and oligofructose.
However, the question of a dose-effect relationship remains
unanswered. Roberfroid et al. (1998)
, in their review
article, present an interesting comparison between the ingested doses
of fructans and the log 10 increase in bifidobacteria. They conclude
that there is no correlation between the two variables of 4 and 20 g/d.
However, they go on to suggest that the initial number of fecal
bifidoacteria, independent of the dose of the fructan, may correlate
with the increases observed. If the levels of fecal bifidobacteria are
sufficiently high to start with, then a further increase in their
numbers may not be demonstrable. Perhaps the does-effect
relationship between the ingestion of fructans and fecal bifidobacteria
should be evaluated in terms of both of the levels and sustainability.
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CONCLUSION
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There is convincing evidence that both the chicory inulin and its
hydrolysis product, the oligofructose, stimulate the growth of
bifidobacteria in humans. A recent in vitro study has indicated that an
oligofructose dosage equivalent to a daily dose of 4 g increased
bifidobacterial numbers, whereas the number of bacteroides, coliform
and gram-positive cocci decreased. At present, there is
considerable interest from the pharmaceutical industries as well as the
food industry to take advantage of the beneficial properties of chicory
inulin and oligofructose in their products.
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FOOTNOTES
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1 Presented at the conference Nutritional and
Health Benefits of Inulin and Oligofructose held May 18–19, 1998 in
Bethesda, MD. This symposium was supported in part by educational
grants from the National Institutes of Health Office of Dietary
Supplements, the U.S. Department of Agriculture and Orafti Technical
Service. Published as a supplement to The Journal of
Nutrition. Guest editors for the symposium publication were
John A. Milner, The Pennsylvania State University, and Marcel
Roberfroid, Louvain University, Brussels, Belgium. 
2 Abbreviations used: BFM, bifidobacteria sp.
fermented milk; I, inulin; OF, oligofructose; SF,
fungal-fructofuranosidase.
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REFERENCES
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1.
Bouhnik Y., Flourie B., Andrieux C., Bisetti N., Briet F., Rambaud J. C. Effects of bifidobacterium sp. fermented milk ingestion with or without inulin on colonic bifidobacteria and enzymatic activities in healthy humans. Eur. J. Clin. Nutr. 1996;50:269-273[Medline]
2.
Clevenger M. A., Turnbull D., Inone H., Enomoto M., Allen J. A., Henderson L. M., Jones E. Toxicological evaluation of Neosugar: genotoxicity, carcinogenicity, and chronic toxicity. J. Am. Coll. Toxicol. 1988;7:643-662
3.
Gibson G. R., Beatty E. R., Wang X., Cummings J. H. Selective stimulation of bifidobacteria in the human colon by oligofructose and inulin. Gastroenterology 1995;108:975-982[Medline]
4.
Gibson G. R., Roberfroid M. B. Dietary modulation of the human colonic microbiota—introducing the concept of prebiotics. J. Nutr. 1995;125:1401-1412
5.
Gibson G., R & Wang X. Enhancement of bifidobacteria from human gut contents by oligofructose using continuous culture. FEMS Microbiol. Lett. 1994;118:121-128[Medline]
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Hidaka H., Eida T., Takizawa T., Tokunaga T., Tashiro Y. Effects of fructooligosaccharides on intestinal flora and human health. Bifid. Microflora 1986;5:37-50
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Hidaka H., Tashiro Y., Toshiaki E. Proliferation of bifidobacteria by oligosaccharides and their useful effect on human health. Bifid. Microflora 1991;10:65-79
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Kleessen B., Sykura B., Zunft H. J., Blaut M. Effect of inulin and lactose on fecal microflora, microbial activity, and bowel habit in elderly constipated persons. Am. J. Clin. Nutr. 1997;65:1397-1402[Abstract/Free Full Text]
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Menne, E., Guggenbuhl, N. Absolonne, J. & Dupont, A. (1997)
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hydrolysate in humans. In: Non-Digestible Oligosaccharides: Healthy
Food for the Colon? Proceedings of the International Symposium,
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Mitsuoka T. Bifidobacteria and their role in human health. J. Indust. Microbiol. 1990;6:263-268
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Reading S., Aramendi S., Gibson G., McCartney A. An in vitro investigation of the minimum fructo-oligosaccharide dose affording a prebiotic effect 1998 Profibre Lisbon, Portugal.
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Roberfroid M. B., Van Loo J.A.E., Gibson G. R. The bifidogenic nature of chicory inulin and its hydrolysis products. J. Nutr. 1998;128:1-9[Free Full Text]
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Wang, X. (1993) Comparative Aspects of Carbohydrate
Fermentation by Colonic Bacteria. Doctoral thesis. University of
Cambridge, Cambridge, U.K.
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Wang X., Gibson G. R. Effect of the in vitro fermentation of oligofructose and inulin by bacteria growing in the human large intestine. J. Appl. Bacteriol. 1993;75:373-380[Medline]
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Williams C., Witherly S., Buddington R. Influence of dietary neosugar on selected bacterial groups of the human faecal microbiota. Microb. Eco. Health Dis. 1993;7:91-97
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ABSTRACT
INTRODUCTION
