This review of the subject of probiotics does not purport to be
comprehensive, but rather merely an introduction.
The colonic microflora are important to
health. The growth and metabolism of the many individual bacterial
species inhabiting the large bowel depend primarily on the substrates
available to them, most of which come from the diet. This has
led to attempts to modify the structure and metabolic activities
of the community through diet using probiotics and prebiotics.
Probiotics are live microbial food
supplements. The best known is the lactic acid bacteria (acidophilus,
(ed)) and bifidobacteria in yoghurts or freeze-dried culture concentrates.
These organisms are non-pathogenic and non-toxigenic, retain viability
during storage, and survive passage through the stomach and small
bowel. (Macfarlane G, Cummings
J, BMJ, 318:999-1003, 1999)
Prebiotics are
non-digestible food ingredients that selectively stimulate the
growth or activities, or both, of lactobacilli or bifidobacteria
in the colon, thereby improving health. The food ingredients most
likely to be effective are the oligosaccharides, including artichokes,
onions, chickory, garlic, leeks. Commercial probiotic preparations
are usually mixtures of lactobacilli and bifidobacteria, although
yeasts such as saccharomyces (as in Kombucha, (ed)) have also
been used. (Macfarlane G, Cummings
J, BMJ, 318:999-1003, 1999)
Acquisition of colonic microflora takes
place early in life and is very much dependent on the nature of
feeding. Compositional changes may also occur with disease or
(certainly) after antibiotic therapy (Roberfroid
M, et al, Nutritional Reviews, 53(5), 1995), the extensive
use of which has led to a flourishing of antibiotic resistance
in common pathogenic bacteria (Canganella
F, et al, Microbiol Res, 151, 167-175, 1996), which
become established when the integrity of the microbiota is impaired
through antibiotic treatment (Macfarlane
G, Cummings J, BMJ, 318:999-1003, 1999). The combination
of probiotics and prebiotics in a synbiotic might improve the
survival of the bacteria crossing the upper part of the gastrointestinal
tract, enhancing their effects in the large bowel and their effects
might be additive or even synergistic (Roberfroid
M, Am J Clin Nutr, 17(6), 2000).
Several health-related effects associated
with the intake of probiotics and their has been proposed as an
alternative to antibiotics (McGroarty
J, FEMS Immun Med Microbiol, 6 251-264, 1993); (Nader de Macias
M, et al, J Food Prot, 56, 401-405, 1993); (Canganella F, et al,
Microbiol Res, 151, 167-175, 1996). Probiotics, because
of their role in the maintenance of normal gastrointestinal flora,
can facilitate human resistance to opportunistic infection and
positively impact the outcome in a variety of clinical situations.
Probiotics have been used successfully to facilitate treatment
of bacterial vaginosis, recurrent urinary infections, diarrhea,
bladder cancer, complications of antibiotic therapy, dysbacteriosis
and dyslipidemias (Catanzaro J,
Green L, Alt Med Rev, 2(4), 1997).
A complex (normal) colonic microflora
is likely to be crucial to both the development and homoeostasis
of the intestinal immune system. Fermentation of non-digestible
dietary substances as well as of endogenous mucus is a major metabolic
function of colonic microflora. The primary functions of colonic
microflora include nutritive, metabolic, immunologic, and protective,
which functions support control of epithelial cell proliferation
and differentiation, metabolism and enterohepatic circulation
of xenobiotics, control of ion concentration and absorption and
control of colonic pH and resistance to infection. (Roberfroid
M, et al, Nutritional Reviews, 53(5), 1995)
The colonic microflora normally presents
a barrier to invading organisms, but pathogens often become established
when the integrity of the microbiota is impaired through stress,
illness, antibiotic treatment, changes in diet, or physiological
alterations in the gut. Bifidobacteria are known to be involved
in resisting the colonisation of pathogens in the large bowel.
Lactobacillus have been shown to colonise the gut and secrete
antimicrobial products that are active against a range of other
micro-organisms. Probiotics and prebiotics seem to be antimutagenic
and or carcinogenic in several ways indicating the potential of
prebiotics and probiotics to reduce or prevent carcinogenesis.
(Macfarlane G, Cummings J, BMJ,
318:999-1003, 1999)
The colonic microbiota affects mucosal
and systemic immunity in the host. Intestinal epithelial cells,
blood leucocytes, B and T lymphocytes, and accessory cells of
the immune system are all implicated. Lactobacilli (acidophilus,
(ed)) bind in vitro to peripheral blood CD4 and CD8 T lymphocytes,
while lactobacilli which adhere to human intestinal epithelial
cells are capable of activating macrophages. Probiotic organisms
interact with the immune system at many levels, including cytokine
production, mononuclear cell proliferation, macrophage phagocytosis
and killing, modulation of autoimmunity, and immunity to bacterial
and protozoan pathogens. (Macfarlane
G, Cummings J, BMJ, 318:999-1003, 1999)
Some evidence suggests a role for probiotics
in reducing the risk of rotavirus-induced diarrhea and colon cancer.
Among the most promising targets for functional foods are the
gastrointestinal functions, including those that control transit
time, bowel habits, and mucosal motility, alleviate lactose intolerance
as well as those that modulate epithelial cell proliferation.
Promising targets are also gastrointestinal functions that are
associated with a balanced colonic microflora, that are associated
with control of nutrient bioavailability (ions in particular),
that modify gastrointestinal immune activity, or that are mediated
by the endocrine activity of the gastrointestinal system. Finally,
some systemic functions such as lipid homeostasis that are indirectly
influenced by nutrient digestion or fermentation represent promising
targets. (Roberfroid M, Am J Clin
Nutr, 17(6), 2000)
Several health-related
effects have been reported in human nutrition studies by different
research groups in several countries. These effects may be used
to justify either functional claims or claims of reduced disease
risk. At present, claims about reduction of disease risk are only
tentative and further research is needed. Among the claims are
constipation relief, suppression of diarrhea, and reduction of
the risks of osteoporosis, atherosclerotic cardiovascular disease
associated with dyslipidemia and insulin resistance, obesity,
and possibly type-2 diabetes. (Sanders
M, J Diary Sci, 76:1819–28, 1993); (Roberfroid M, et al,
Nutritional Reviews, 53(5), 1995); (Salminen S, et al, 70:347–58,
1996); (Mortomi M, Asia Pac J Clin Nutr, 5:29–30, 1996);
(Catanzaro J, Green L, Alt Med Rev, 2(4), 1997); (Macfarlane G,
Cummings J, BMJ, 318:999-1003, 1999); (Roberfroid M, Am J Clin
Nutr, 17(6), 2000).