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2003). As we age, changes occur in the composition of the intestinal micro-
biota that may contribute to an increased level of undesirable microbial
metabolic activity and subsequent degenerative diseases of the intestinal
tract (Saunier and Dor´, 2002; Guarner and Malagelada, 2003).
Modifying the composition of the intestinal microbiota to restore or
maintain a beneficial population of microorganisms would appear to be a
reasonable approach in cases where a deleterious or sub-optimal population
of microorganisms has colonized the gut. The two genera most often pro-
posed as beneficial bacteria with which to augment the intestinal microbiota
are the lactobacilli and bifidobacteria, both of which are numerically com-
mon members of the human intestinal microbiota. Two approaches are used
to increase the number or proportion of these bacteria in the gut. The first is
by directly supplementing the intestinal microbiota by consuming live bac-
teria, ''probiotics'', in foods or pharmaceuticals. The second is by consuming
dietary components, ''prebiotics'', which selectively stimulate the prolifera-
tion and/or activity of these purportedly beneficial organisms that are already
resident within the intestinal microbiota (Gibson et al., 2005). Most prebiotics
identified to date are non-digestible, fermentable carbohydrates, particularly
oligosaccharides and include the lactose derivatives, GOSs and lactulose.
Despite a diversity of structures, most prebiotics stimulate the prolifera-
tion of bifidobacteria in particular and are sometimes referred to as ''bifidus
factors'' or ''bifidogenic factors'' (Table 5.1). A number of largely prophylactic
health targets have been proposed for prebiotics stemming from alterations to
the composition or fermentative activity of the microbiota in response to
the availability of a selectively utilized carbohydrate source. These include
protection against enteric infections, increased mineral absorption, immuno-
modulation for the prevention of allergies and gut inflammatory conditions
(Figure 5.8), and trophic effects of short-chain fatty acids (SCFA) on the
colonic epithelium, faecal bulking and reduced toxigenic microbial metabolism
that may reduce risk factors for colon cancer (Figure 5.9).
5.9.4.1.
Applications of GOSs in Infant Nutrition
The composition of the human intestinal microbiota changes naturally
with age, and in early infancy the microbiota is believed to be particularly
important in correct functioning of the gut and maturation of the immune
system. Indeed, differences have been observed between the composition
of the microbiota in allergic and healthy infants including reduced numbers
of bifidobacteria and a more adult-like profile of Bifidobacterium species
(Kirjavainen and Reid, 2006). Bifidobacteria colonize the human intestinal
tract during or soon after birth and in breast-fed infants eventually dominate
the
microbiota
(Harmsen
et
al.,
2000).
The
numerical
dominance
of
