Irritable Bowel Syndrome, Small Intestinal Bacterial Overgrowth, and Probiotics

By Jun Kim Ph.D.
Irritable bowel syndrome (IBS) affects millions of people worldwide. It is a chronic disorder that affects the colon and causes cramping, abdominal pain, bloating, gas, diarrhea, and constipation. Unlike inflammatory bowel disease (IBD), IBS does not produce destructive inflammation and usually shows no sign of disease or abnormalities. Because much is still unknown about IBS currently there is no cure and only the symptoms can be treated. Over the past decade, studies have been suggesting new mechanisms of IBS. Some of these studies suggest small intestinal bacterial overgrowth, or SIBO, as a potential cause of IBS.

In 1977, Vantrappen et al. discovered that patients with bacterial overgrowth had abnormal motility in the intestines [1]. Further studies confirmed the finding in IBS patients [2], and IBS symptoms decreased when the bacterial overgrowth was controlled with antibiotics. For example, a study of 202 patients with IBS found that 78% of the patients with IBS also had bacterial overgrowth. When treated with antibiotics, 53% of the patients with bacterial overgrowth reported improvement in their IBS symptoms [3]. In another study, 84% of 111 patients with IBS had bacterial overgrowth, and again, treatment with antibiotics led to a reduction in IBS symptoms [4]. Despite the variability in the percentage of IBS patients having bacterial overgrowth, for those who do effective treatment with antibiotics has been confirmed in different studies [5,6].
A number of studies have been conducted to evaluate the benefits of probiotics on IBS and demonstrated symptom improvement [7–10]. Experimental studies have shown that probiotics can compete with pathogens, produce bacteriocins, inhibit bacterial translocation, enhance mucosal barrier function, and regulate immune system [11–18]. For SIBO, direct evidence of benefit comes from studies of probiotics in experimental models of translocation of gastrointestinal bacteria into other sites in the body. For example, Adawi et al. showed that lactobacillus plantarum reduced the total number of bacteria translocated to mesenteric lymph nodes, portal blood, and the liver [19], and others demonstrated similar results in other animal models [20,21]. Human studies also suggest that L. plantarum may either prevent or delay symptom recurrence after antibiotic therapy [22]. One study showed that both L. casei and L. acidophilus proved effective for bacterial overgrowth-related chronic diarrhea [23].
With different probiotic doses and strains, the studies with probiotics are difficult to be compared. In general, probiotics appear to possess a number of properties that could be of benefit to SIBO. Their use as a therapy, however, requires validation by well-conducted clinical trials.
Disclaimer: The above article is sponsored by Thryve, the world’s first Gut Health Program that incorporates microbiome testing and personalized probiotics to ensure a healthier gut, happier life, and a brighter future.


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