NFANTS AND THE E LDERLY
15.7.1 I NFANTS AND THE E LDERLY
The gut microflora of breast-fed infants is primarily constituted of bifidobacteria. 79 The protective effect of bifidobacteria against enteropathogens has been demon- strated both in vitro and in vivo. Bifidobacteria are essential for the constitution of the infant gastrointestinal defense barrier and for stimulation of early immunological
responses. 80 Differences exist between the intestinal microflora of breast-fed and formula-fed infants. Extensive comparative studies have repeatedly shown a more diverse bacterial community and lower numbers of bifidobacteria in feces of formula-
fed infants. 81 These observations were correlated to a higher risk of pathogen colo- nization. Human breast milk contains oligosaccharides composed of sialic acid, N- acetyl glucosamine, L-fucose, D-glucose, and D-galactose. 82 These human oligosac- charides are naturally occurring prebiotics that enhance protection against pathogens by a treble mechanism: (1) they increase selectively the bifidobacteria and beneficial populations of the gut, (2) they act as decoy receptors to pathogenic bacteria by mimicking the oligosaccharide portion of epithelial glycoproteins, and (3) their colonic fermentation results in the production of SCFAs, such as acetate and lactate, which acidify the intestinal content and prevent the proliferation of pathogens. The composition and structure of human milk oligosaccharides cannot be reproduced industrially. Fructo-oligosaccharides, lactulose, and galacto-oligosaccharides are the best candidates for supplementing formula milk. Recent studies of prebiotic supple- mentation in term and preterm infants showed an increase in fecal bifidobacteria and an improvement of intestinal passage (Table 15.7). A mixture of fructo-oligosac- charides and galacto-oligosaccharides may reproduce more closely the composition
of breast milk than the addition of one type of oligosaccharide only. 53 At weaning age, the gut microbiota acquires a diverse profile that remains relatively constant
through adult life. With aging, however, the intestinal homeostasis tends to be compromised. Inves- tigations in the elderly showed a decrease in the proportion of bifidobacteria and a higher occurrence of enterobacteria species. 87,88 The use of oligosaccharides to maintain the prevalence of bifidobacteria in the gut microbiota is currently under
Probiotics, Prebiotics, and Synbiotics
TABLE 15.7 Clinical Trials Investigating Change in the Microflora of the Infant
Study Design
Moro et al. 53 galacto-oligosaccharides
Formula
28 days
0.04 g/l and
Randomized, placebo-controlled,
Increase in
0.08 g/l
parallel trial, n = 60 term infants
bifidobacteria
Fructo-oligosaccharides +
Boehm et al. 83 galacto-oligosaccharides
Formula
28 days
0.3 g/day
Randomized, placebo-controlled,
Increase in
parallel trial, n = 42 preterm infant
bifidobacteria
1–3 g/day
Randomized, placebo-controlled,
No significant change
Guesry et al. 84
parallel trial, n = 53 infants (1 month
of fecal microflora
old)
Oligosaccharides mix from
Romond et al. 85 fermentation of lactose by
Randomized, double-blind, placebo-
Increase in
bifidobacteria; higher Bifidobacterium breve C50
controlled, parallel trial, n = 35
newborn infants
production of anti- poliovirus IgA
Randomized, parallel trial, n = 42
No prevalence of
Rubaltelli et al. 81
newborn infants
bifidobacteria
Crossover trial, n = 6 infants (2–10
Increase in
Nagendra 86
weeks old)
bifidobacteria; decrease in coliform species
Note : N.D. = not determined.
Functional Food Carbohydrates
TABLE 15.8 Clinical Trials Investigating Changes in the Elderly Gut Microflora with Consumption of Prebiotics
Prebiotic Study Design
Outcomes
Reference
Inulin n = 25 elderly Increase in bifidobacteria Klessen et al. 89 Isomalto-
n = 18 senile men + 6 Increase in bifidobacteria Kohmoto et al. 90 oligosaccharides
healthy men Fructo-
n = 19 elderly Increase in bifidobacteria and Guigoz et al. 91 oligosaccharides
bacteroides; decrease in inflammatory immune response
investigation. Few in vivo studies are available, but inulin, fructo-oligosaccharides, and isomalto-oligosaccharides showed a positive modulation on the fecal microflora
of the elderly (Table 15.8). Development of specific synbiotic combinations geared toward protection against enterobacteria are currently under study. 92