Probiotics are a group of live microorganisms and yeasts that may beneficially affect the body by improving the balance of microflora (i.e. bacteria that are naturally occurring in the small and large intestine, mouth and vagina). The scope of this article will focus on the benefits of probiotics for a healthy and balanced digestive system.
Thus far, scientists suggest that a healthy human digestive tract contains about fourteen various genus of microorganisms, making a grand total of approximately 400 types of bacteria that reduce the growth of harmful bacteria and promote a healthy digestive system. The largest group of probiotic bacteria in the intestine is lactic acid bacteria, of which Lactobacillus acidophilus (found in yogurt) is the best known. However, there are other species of Lactobacillus that have also been shown to be beneficial, such as L. plantarum, L. rhamnosus, L. casei and L. bulgaricus.
The Function of Microbes in the GI Tract
The gastrointestinal tract of animals represents a complex ecosystem in which a delicate balance exists between the intestinal microflora and the host. The host and microflora live in a synergistic environment – the host providing a comfortable environment for the microbes to survive while the microbes thrive and produce beneficial metabolic byproducts that aid the host’s GI tract and immune system. This synergistic relationship begins to develop while we are babies, starting at delivery and continuing during breastfeeding and receiving kisses from family and friends.
The inhabitation of microbes in a developing GI tract has been hypothesized to not only be important in the neonatal period and during infancy, but also in an individual’s health throughout life. The small intestine is lined with lymph nodes that support our immune system. The byproducts and metabolites of the intestinal microflora developed during infancy are important for maturation of the immune system, the development of normal intestinal form and structure, and to maintain a chronic and immunologically balanced inflammatory response. The microflora reinforce the barrier function of the intestinal lining, helping to prevent the attachment of pathogenic microorganisms and the entry of allergens.
Some members of the microflora may contribute to the body’s requirements for certain vitamins, including biotin, pantothenic acid and vitamin B12.  Alteration of the microbial flora of the intestine, which may occur with the use of antibiotics, disease, and aging, can negatively affect its beneficial role. This is where the potential benefits of supplementing with probiotics may help to balance or re-balance what has been destroyed.
When to Use Probiotics
If you believe that probiotics may be beneficial for your condition, but you do not know what to look for on a product’s label, here is what the current research suggests:
Diarrhea
Among the probiotics, only S. boulardii, Enterococcus faecium and Lactobacillus species have been useful in preventing antibiotic-related diarrhea. S. boulardii appears to be the most superior form of treatment when diarrhea is caused by Clostridium difficile, a bacterium often associated with antibiotic related diarrhea. The results of some early studies suggest that probiotics found in yogurt may help prevent diarrhea caused by antibiotics. However, more studies are needed to confirm that yogurt is effective. To offer benefits, the yogurt must contain active cultures.
Anti-Inflammatory for GI Conditions
Because of a reduced fecal concentration of various probiotics in individuals with active ulcerative colitis, Crohn’s disease, active pouchitis, inflammatory bowel disease, and irritable bowel syndrome, researchers have noted that probiotics may be beneficial for individuals with these conditions. However, thus far, the
results have been inconclusive and more research is needed.
Allergies
Some lactic acid bacteria, including L. plantarum, L. rhamnosus, L. casei and L. bulgaricus, have demonstrated immuno-regulatory effects that may help protect against some allergic disorders. There is some evidence that some of these probiotic strains can reduce the intestinal inflammation associated with some food allergies, including cow’s milk allergies among babies.  Research has shown that breastfed infants given Lactobacillus significantly improved atopic dermatitis or eczema, compared with infants not exposed to this probiotic.
Anti-Carcinogenic
There are in vitro studies, as well as animal and some preliminary human studies suggesting that some probiotics can bind and inactivate some carcinogens, which can directly inhibit the growth of some tumors and inhibit bacteria that may convert pre-carcinogens into carcinogens.  L. acidophilus and L. casei have exhibited the latter activity in human volunteers. There is some preliminary evidence that L. casei may have reduced the recurrence of bladder tumors in human studies, although confirmatory trials are needed.  Animal work has suggested that some lactic-acid bacteria may help protect against colon cancer.  Again, more research is needed.
Summary
The effectiveness of probiotics is dependent upon their ability to survive in the acidic stomach environment and the alkaline conditions in the upper small intestine, as well as their ability to adhere to the intestinal lining and to colonize in the colon.  Some probiotics, such as L. casei, L. rhamnosus, and L. plantarum, are better able to colonize than others.  A major problem is that there are many probiotic products available, and not all of them have been tested for every potential treatment listed above. These products contain various Lactobacillus and Bifidobacterium strains and combinations of probiotics and prebiotics. Additionally, typical doses of probiotics range from one to ten billion colony-forming units (CFU) a few times a week.  Because of the inconclusive data of probiotics, the optimal number of CFU’s for a healthy GI tract is unknown. Trial-and-error may be needed to find the most beneficial dose, but there is very little risk in overdosing.  Usually probiotics are well-tolerated, unless you have a prior condition that may warrant caution.  Discuss the use of probiotics with your physician or healthcare provider.  The animal and in vitro studies continually show there may be more benefits of probiotics to help with the delicate balance of our bodies.