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