Irritable bowel syndrome (IBS) is common gastrointestinal problems. It is characterized by abdominal pain or discomfort, and is associated with changes in stool frequency and/or consistency. The etiopathogenesis of IBS may be multifactorial, as is the pathophysiology, which is attributed to alterations in gastrointestinal motility, visceral hypersensitivity, intestinal microbiota, gut epithelium and immune function, dysfunction of the brain-gut axis or certain psychosocial factors. Current therapeutic strategies are often unsatisfactory. There is now increasing evidence linking alterations in the gastrointestinal microbiota and IBS. Probiotics are living organisms which, when ingested in certain numbers, exert health benefits beyond inherent basic nutrition. Probiotics have numerous positive effects in the gastrointestinal tract. Recently, many studies have suggested that probiotics are effective in the treatment of IBS. The mechanisms of probiotics in IBS are very complex. The purpose of this review is to summarize the evidence and mechanisms for the use of probiotics in the treatment of IBS.
Since Elie Metchnikoff first published “The prolongation of life: optimistic studies” in 1907, the concept of probiotics is 100-year-old now. In 1998 Guarner et al defined probiotics as living microorganisms that have benefits for the gastrointestinal tract and its immune function after being ingested. In 2003 the concept of “immune function of probiotics” was introduced, including the fact that probiotics modulate the immune response throughout the mucosa associated lymphoid tissue system; this idea maintains the concept that intestinal mucosa and intestinal microflora constitute an anatomical-functional unit that regulates both the cell-mediated and humoral immune responses and the local production of cytokines. In 2008, a review defined probiotics as living microorganisms, which when ingested in certain numbers, exerted health benefits beyond inherent basic nutrition.
Now probiotics are becoming an increasingly important part in the diet of everyday life, as their general and gastrointestinal beneficial effects are being gradually proven. It has become necessary to harmonize marketing criteria, evaluate the efficacy of probiotics, and correctly define what is a probiotic, what the effective doses are, and whether they are completely safe. Probiotics are defined at three levels: genus, species and strain; it is essential to understand that their properties depend on all three and cannot be assigned to other similar ones, even if they share the same genus and species. The therapeutic benefits of a strain of probiotics cannot be extended to other strains, and their efficacy has to have been proven individually. Therefore, we shall now examine evidence available to date. Usually probiotics are certain types of Streptococcus, Lactobacilli, and Bifidobacteria, but also other non-pathogenic bacilli such as E. coli-Nisle1917 and yeasts such as Saccharomyces boulardii. The best known and most widely used probiotics are:
- Lactobacillus plantarum 299v
- Lactobacillus rhamnosus LGG
- Lactobacillus reuteri
- Lactobacillus acidophilus
- Lactobacillus casei
- Bifidobacterium infantis, lactis or brevis
Probiotics can be administered not only as functional foods, but also in pharmaceutical forms similar to medicines. For a probiotic to be effective, five conditions must be fulfilled:
- it must not be toxic or pathogenic;
- it must have a proven beneficial effect on the host;
- it must contain a sufficiently large number of viable microorganisms per unit;
- it must be capable of surviving in the intestine, reproducing, maintaining itself, and having intraluminal metabolic activity;
- it must remain viable during storage and use.