Probiotics
Figure 2: Relative Proportions of Bifidobacterial Species in the Adult and Infant Gut
10 20 30 40 50 60 70 80
0 Adult Source: Turoni et al., 2009.22
Figure 3: Relative Proportions of Bifidobacterial Species in Mucosal and Fecal Samples
10 20 30 40 50 60 70 80
0 Infant
Prebiotics, Supplements, and Functional Foods The potential benefits of boosting the population of bifidobacteria in the gut have prompted the development of a growing range of dietary supplements and so-called functional foods. These products aim to increase bifidobacterial numbers by either introducing exogenous live bifidobacteria (probiotics), or encouraging proliferation of native bifidobacteria with supplementary prebiotics (or both, i.e. synbiotics). As outlined above, increasing evidence suggests that the human gut harbors specific species or even strains of bifidobacteria so supplementation with probiotics alone should use carefully selected bacteria. Another potential limitation of probiotic supplements is that they may not have a significant effect on mucosal bacterial populations, while increased numbers of bacteria in feces may not necessarily translate into health benefits.31
In a
study on 12 volunteers comparing normal yoghurt with B. longum- enriched yoghurt, there was increased fecal bifidobacteria but no change in factors such as short-chain fatty acid concentrations. The authors concluded that fecal flora is stable to probiotic intervention. The ability of prebiotics such as inulin to boost native bifidobacterial populations thus appears to be a potentially important advantage. Currently, there are no recommended daily amounts for prebiotics, but evidence suggests that consuming at least 5g inulin/day has a beneficial effect on gut bacterial flora and digestive health.32–34
Adult Source: Turoni et al., 2009.22 B. breve, B. adolecentis, B. longum, and B. pseudocatenulatum.21,22,24 Some
authors have suggested that the number of species changes with increasing host age, but a recent study by Turroni et al. reported a similar range of bifidobacteria in adults and infants, although the relative numbers of each species differed (see Figure 2).22,25
There is
evidence that bifidobacteria may decline in elderly people in at least some European populations.26
Much of the published data on intestinal flora is based on fecal sample analysis, but this may reflect transient populations in the gut lumen rather than a permanent bacterial population in mucosa-associated biofilms. Turroni et al. found different bifidobacterial species compositions in fecal and mucosal samples (see Figure 3).22
This may complicate interpretation
of fecal bifidobacterial populations in infants, and mucosal biopsy for this age group would be unlikely to be performed purely to assess commensal bacterial populations. Bifidobacteria appear to play a key role as part of a
60 Infant
Impact of Supplementary Inulins on Gut Microflora Both in vivo and in vitro studies have shown that adding inulin (or inulin-type prebiotics) to the diet leads to increased bifidobacterial populations in the gut.15,16,23,27,35
A relatively high dose (15g/day) of inulin
or oligofructose has been linked with bifidobacteria becoming numerically predominant in the human colon in just 15 days.15
Adding chicory inulin
to the artificial gut model known as the Simulator of the Human Intestinal Microbial Ecosystem (SHIME) revealed enhanced growth of bifidobacteria in both proximal and distal colon, as measured using PCR.23
There is also some evidence that prebiotic supplementation with a mixture of inulin and oligofructose can boost bifidobacterial populations in mucosal biofilms.16
stable adherent microbiota that helps to maintain the mucosal barrier.27 Any disruption to this microbiota, for example due to declining numbers of bifidobacteria, could allow the mucosal barrier to become impaired, leaving the mucosa susceptible to attack by pathogens, inflammation, and disease (see Figure 4).27
Bifidobacteria also appear to protect against
potentially harmful micro-organisms both by competitive exclusion and effects of inulin breakdown products.28
organic acids produced by lactic acid bacteria may have a stronger bactericidal effect than hydrochloric acid against pathogens such as Shigella, independent of pH value.29
Inulin fermentation by bifidobacteria
also produces exopolysaccharides that hinder pathogen growth and directly inhibit the effects of bacterial toxins on host cells.28,30
In vitro evidence suggests that the
Mucosal biopsies before and after supplementation revealed significant increases in bifidobacteria in both the proximal and distal colon (see Table 2).16
In vivo research has linked an increased
proportion of bifidobacteria in gut mucosal flora following inulin/ oligofructose supplementation with improved stability of the mucosa and associated biofilm.27
Increased stability was linked with enhanced
mucosal architecture, i.e. deeper crypts, greater microvillus height, and increased numbers of goblet cells.27
Rats consuming an inulin-enriched US GASTROENTEROLOGY & HEPATOLOGY REVIEW
B. animalis ssp. lactics B. psuedocatenulatium B. bifidum B. adolescentis B. psuedolongum
B. breve B. dentium B. longum
B. animalis ssp. lactics B. psuedocatenulatium B. bifidum B. adolescentis B. psuedolongum
B. breve B. dentium B. longum
% Bifidobacterial species
% Bifidobacterial species
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