Chemistry Reference
In-Depth Information
food supply has limited our exposure to the more beneficial organisms previously
consumed on a daily basis. The science of prebiotics and probiotics is now focused
on attempting to identify those specific beneficial nutrients and species.
13.4 MEChANIsMs oF ACTIoN
Prebiotics and probiotics are not as similar as their names suggest. Prebiotics
basically provide the food for all sorts of microorganisms. A beneficial prebiotic
increases the number of less aggressive or beneficial organisms in the bowel, pro-
duces short-chain fatty acids, which protect the bowel lining and prevent invasion
of harmful organisms, lowers the intestinal pH, which alters the growth of some
organisms as well as increases calcium absorption and possibly has some immuno-
modulation effects.
2
Prebiotics, therefore, act only on natural flora already present
in the bowel.
To be a successful probiotic, microorganisms must be ingested in live or dor-
mant form, be able to maintain sufficient viable microorganisms that survive the
host's digestive process, as well have demonstrable health effects without significant
adverse effects.
15
Probiotics act by numerous different mechanisms; however, adher-
ence to the intestinal epithelium is often felt to be important for the interaction with
the gastrointestinal immune system by inducing the immunomodulating benefits,
such as enhancing immunoglobulin A (IgA) production and stimulating cytokines.
16
Other functions of probiotic bacteria include their ability to produce antimicrobial
substances, such as bacteriocins, hydrogen peroxide, and biosurfacants. They may
also act to lower intestinal pH by stimulating lactic acid-producing organisms, which
favors growth of more beneficial organisms. Some probiotics enhance colonization
resistance by competing with pathogens for binding and receptor sites and for avail-
able nutrients required by pathogenic organisms.
17
A probiotic is most beneficial
when it can adapt to healthy intestinal flora, not displace the native bacteria already
present.
13.5 ClINICAl sTuDIEs
13.5.1 Prebiotics
As a result of the relatively recent recognition of the potential benefits of pre-
biotics, the number of randomized controlled studies is limited. It has been recog-
nized that the human milk oligosaccharides, the third most abundant component
of breast milk, are bifidogenic and one mechanism for the protective effect of the
breastfed infant against many diarrheal conditions.
18,19
The composition of human
milk oligosaccharides is very complex and more than 100 different oligosaccharide-
like structures are known. The concentration of these compounds in breast milk
changes according to different lactation phases; it is higher in colostrum than in
transitional and mature milk. These findings have led to the study of supplementing
