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longum, and adolescentis); Enterococcus (facecum and faecalis); and Lactobacillus
(acidophilus, paracasei, rhamnosus, and reuteri) (Kawese, 1982; Rasic, 1983; Teitel-
baum and Walker, 2002). Probiotic bacteria avoidably alter the intestinal microflora
balance, inhibit growth of harmful bacteria, promote good digestion, boost immune
function, and increase resistance to infection. People with flourishing intestinal
colonies of beneficial bacteria are better equipped to fight the growth of disease-
causing bacteria (De Semone et al., 1993). Lactobacilli and bifidobacteria maintain
a healthy balance of intestinal flora by producing organic compounds such as lactic
acid, hydrogen peroxide, and acetic acid that increase the acidity of the intestine
and inhibit the reproduction of many harmful bacteria (Kawese, 1982; Rasic, 1983).
Probiotic bacteria also produce bacteriocins, which act as natural antibiotics to kill
undesirable microorganisms (Barefoot and Klaenhammer, 1983).
Immune function tends to decline with age. A double-blind clinical study involv-
ing daily supplementation of elderly people with Bifidobacterium lactis (a particular
strain of bifidobacteria) resulted in a significant enhancement of the immune function
(Arunachalam et al., 2000). Benefits were apparent after only 6 weeks of supple-
mentation. Research has also shown that both topical and oral use of acidophillus
can prevent yeast infection caused by candida overgrowth (Ekmer et al., 1996). For
example, regular ingestion of probiotic bacteria may help to prevent vaginal yeast
infection (Hilton et al., 1992; Reid et al., 1996).
Diarrhea flushes intestinal microorganisms out of the gastrointestinal tract, leav-
ing the body vulnerable to opportunistic diseases. Replenishing the beneficial bac-
teria with probiotic supplements can help prevent new infections. The incidence of
“traveler’s diarrhea” caused by pathogenic bacteria in drinking water or undercooked
foods can be reduced by the preventive use of probiotics (Scarpignato and Rampal,
1995). Most people associate lactobacilli with L. acidophilus, the most popular
species in this group of probiotic bacteria. However, research shows that other
Lactobacillus species may be beneficial as well. For example, L. rhamnosus and
L. plantarum appear to be protective bacteria. They are involved in the production
of several “gut nutrients” such as short-chain fatty acids and the amino acids arginine,
cysteine, and glutamine (Bengmark, 1996). These bacteria have been reported to
remove toxins from the gut and exert a beneficial effect on cholesterol levels (Beng-
mark, 2000). Likewise, a probiotic Saccharomyces boulardii has been shown to
prevent diarrhea in several human trials (Golledge and Riley, 1996). A double-blind
research study with critically ill patients found that this strain of yeast prevented
diarrhea when 500 mg were taken per day (Bleichner et al., 1997). Probiotics are
also important in recolonizing the intestine during and after antibiotic use. Probiotic
supplements replenish the beneficial bacteria, preventing up to 50% of infections
occurring after antibiotic use (Louzeau, 1993).
Probiotics also promote healthy digestion. Enzymes secreted by probiotic bac-
teria aid digestion. Acidophilus is a source of lactase, the enzyme needed to digest
the sugar lactose, which is lacking in lactose-intolerant people (McDonough et al.,
1987). Fructo-oligosaccharides are naturally occurring carbohydrates that cannot be
digested or absorbed by humans. They support the growth of bifidobacteria, one of
the beneficial bacterial strains (Williams et al., 1994). Due to this effect, some doctors