Human Digestive SystemSmall intestinal bacterial overgrowth (SIBO) is much more common among irritable bowel syndrome (IBS) sufferers than it is among healthy individuals and affects sub-groups of sufferers to different degrees, according to the latest research.

Important findings from the study include SIBO being much more common among the diarrhoea-predominant sub-type of IBS (IBS-D)  and also among female IBS sufferers. In addition, a large amount of bloating experienced by those with IBS was found to be strongly associated with the presence of SIBO.

The study was carried out by researchers from the Department of Gastroenterology at the GB Pant Hospital, New Delhi, India, and the results are published in the Journal of Gastroenterology and Hepatology.

As the name suggests, small intestinal bacterial overgrowth refers to a situation in which there is excessive growth of bacteria in the small intestine. In a recent interview with BBC radio, Dr. Mark Pimentel of Cedars-Sinai Medical Center in Los Angeles, California, explained that the small intestine is usually relatively free of bacteria and other microbes, in contrast to the large intestine (or colon) which is teeming with such life.

The latest study involved 59 consecutive IBS patients being treated at GB Pant Hospital as well as 37 healthy controls. Both the patients and the control subjects were evaluated for the presence of SIBO using a glucose breath test (GBT). This diagnostic test involved giving each individual a drink containing 100 grams of glucose after an overnight fast. The levels of hydrogen and methane were then measured in their breath since bacteria produce these gases as by-products of their metabolism. A persistent rise in breath hydrogen and/or methane of greater than 12 parts per million (ppm) above pre-test levels was considered diagnostic of SIBO.

Of 59 patients 27 were diarrhoea predominant (D-IBS), 11 were constipation predominant (C-IBS) and 21 were mixed type (M-IBS). Median age of patients (34 [18-47] years) were comparable to controls (35 [20-48] years) (P = 0.21). Patient group was similar to HC in gender distribution (male 41/59 [69.5%]vs 25/37 [67.6%], P = 0.36).

The researchers report tht SIBO was present in 23.7 per cent of IBS patients but in only 2.7 per cent of the healthy study participants. A number of previous studies have produced similar results. What is interesting about this study is that more patients with IBS-D had SIBO as compared to non-IBS-D (37% vs 12.5%) with only 9 per cent of constipation-predominat IBS (IBS-C) patients having SIBO. Mixed- or alternating-IBS (IBS-M/A) feel inbetween. Another important finding was that women with IBS were much more likely to have SIBO than men with IBS (44.4% vs 14.6%). Finally, a history of bloating was found to be highly predictive of the presence of SIBO - 47.8 per cent of IBS patients badly affected by this symptom had SIBO compared to only 8.3 per cent of those for whom bloating was not a major issue.

Dr. Pimentel, who himself has conducted research in this area and is a leading expert on IBS and SIBO, said that excessive growth of bacteria in the small intestine is a problem because this is where the food we eat is digested and absorbed. Any bacteria present can hijack the food particles and nutrients for themselves with the result being the production of large amounts of hydrogen and methane gases which trigger the common IBS symptoms of bloating, abdominal pain, flatulence, and diarrhoea.

The results of this latest study from India are important because, if replicated, they indicate which IBS patients are most likely to have an issue with SIBO. Physicians will know to be particularly suspicious of SIBO involvement in female patients with IBS-D who compain of bloating. Identifying those IBS patients affected by SIBO is important since Dr. Pimentel, and others, have found that treatment with specific antibiotics such as rifaximin are effective in eardicating the bacterial overgrowth and reducing symptoms while being relatively free from side-effects.

Source: Sachdeva S Rawat AK Reddy RS Puri AS (2011) Small intestinal bacterial overgrowth (SIBO) in irritable bowel syndrome: frequency and predictors Journal of Gastroenterology and Hepatology 6(Suppl 3):135-8



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