Summary
Probiotics include very different bacteria: some are Gram (+) and others Gram (-); some adhere to the mucosa and others inhabit the lumen. For this reason, their actions are very different and it is not possible to extrapolate the benefit of one particular strain to another. There are multiple probiotics available. However, there are few who have truly demonstrated a clear benefit in human health. This article describes the difficulties and possibilities of studies carried out on the effects of probiotics in various gastrointestinal conditions, analyzing the possibility of indicating these products in them.
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Introduction
The World Gastroenterology Organization defines probiotics as live microorganisms that when administered in adequate quantities confer a benefit to the health of the host 1 . Being strict in the application of this definition, most of what is promoted as probiotics is not: many correspond to lysis of bacteria (and not live bacteria), often the microorganisms do not come in adequate amounts, or simply there are no studies scientists who have shown benefit in the health of humans. In general they correspond to bacteria, most often inhabitants of the human gastrointestinal tract, although fungi such as Sacaromyces boulardii have also been used. Lactobacilli and bifidobacteria have been the most used. Its use has increased in recent years. A recent systematic review showed that probiotics have been tested in 68 clinical conditions, although not all of them have shown a benefit 2 .
Developing
Actions of probiotics
Probiotics include very different bacteria, some are Gram (+) and others Gram (-). Some adhere to the mucosa and others inhabit the lumen. For this reason, their actions are very different and it is not possible to extrapolate the benefit of one particular strain to another 1 . Multiple effects of these microorganisms have been described (Table 1): bacteria in the colon can produce different amounts and types of gases after their metabolism of carbohydrates. They can also inactivate bile salts by conjugation, decreasing their choleretic effect. Some are capable of producing short chain fatty acids, which stimulate peristalsis and intestinal transit. Bacteria that adhere to the mucosa of the intestine prevent other (potentially deleterious) bacteria from doing so. For example, Sacromyces boulardii can cleave Clostridium difficile toxin. Thus, many probiotics have shown an anti-inflammatory effect in colitis models. Given the various effects, there are strains that are potentially useful in modulating the gas, others in decreasing diarrhea, others in improving constipation.
Probiotics and irritable bowel syndrome (IBS)
Although there are multiple studies carried out, the vast majority are not optimal from the methodological point of view, being the small sample size and the lack of a control group the most frequent problems. The latter is especially important in a disease with a high placebo-type response rate. Thus, for example, Flosh and collaborators only found 8 valid works in a systematic review of 30 years of bibliography 3 .
Of the eight works mentioned, the probiotic Bifidobacterium infantis 35624 was used in three. In all the works there was a benefit in the patients with IBS. O'Mahony and colleagues evaluated this probiotic in 75 patients with IBS, comparing it with Lactobacillus salivarius UCC4331 and placebo milk (heat-inactivated bacteria). A significant improvement in the scores of abdominal pain and distension was demonstrated, having a discrete effect on bowel movements. Whorwell and colleagues conducted a multicenter study, with a total of 262 patients with IBS, comparing three different doses of Bifidobacterium infantis 35624 and placebo. A significant decrease in symptom scores was observed, obtaining adequate relief by 60% (versus 40% in placebo), with a number needed to treat (NNT) of 5 5 . Thus, in the technical review of the use of probiotics in IBS published in Am J. Gastroenterology in 2009, it is maintained that " Bifidobacterium infantis 3562 4 has shown efficacy in the improvement of IBS symptoms" 6 ,
stipulating that there is not enough evidence to suggest the use of other probiotics. Unfortunately, this probiotic is not yet available in Chile.
Probiotics and constipation
The use of Lactobacillus casei shirota in constipation has been shown to be beneficial 7 . However, this product is not available in Chile. There are several studies on the use of Bifidobacterium animalis DN 173010 (strain present in a brand of yogurt and dairy products available in Chile), which has shown benefit in the symptom constipation. In 2007, a study was published in 267 patients with constipation-like IBS with the use of this probiotic daily for three weeks. In the overall analysis there was no improvement in digestive symptoms when compared with placebo. However, in the subgroup of patients who had less than three bowel movements per week, Bifidobacterium animalis DN 173010 showed a clear improvement in intestinal transit (increase in the number of stools twice), with decreased abdominal distension and discomfort, without major effect on pain 8 . It seems then that all effects are mediated by an improvement in intestinal transit.
Conclusions
There are multiple probiotics available. However, there are few who have truly demonstrated a clear benefit in human health. Regarding digestive symptoms and diseases, Bifidobacterium infantis 35624 has shown a benefit on the symptoms of IBS, independently of an effect on intestinal transit. Bifidobacterium animalis DN 173010 has shown a benefit in improving intestinal transit (and secondarily other symptoms) among patients with less than three stools per week. It should be noted that adverse effects have been reported with the use of probiotics, but in the context of critical or immunosuppressed patients. Even more information is required in order to increase the indications of these products.