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The Emerging Science of Probiotics in IBS

Irritable Bowel Syndrome (IBS) is the most common functional bowel disorder diagnosed by primary care physicians and gastroenterologists (Ladabaum). Estimation of the exact prevalence of IBS is complicated, because up to 70 percent of persons with IBS symptoms do not seek medical treatment (Drossman). The ratio of female-to-male sufferers is approximately 2:1. IBS affects up to one in five Americans and is second only to the common cold as a leading cause of workplace absenteeism in the U.S. IBS costs the U.S. healthcare system up to an estimated $20 to 25 billion annually in direct and indirect costs. (Ladabaum, Drossman, John Hopkins). IBS is an episodic condition that is accompanied by a wide range of symptoms, including abdominal pain and discomfort, bloating, and altered bowel function (constipation and/or diarrhea).

Because IBS is not associated with excess mortality, the medical community has not until recently considered IBS to be a disease. Instead, it was considered to be a somatic response to excessive stress. However, there is significant morbidity associated with IBS, as patients suffering from IBS-related symptoms endure a great deal of distress, often preventing them from participating in activities they would normally enjoy. The impact of IBS on quality of life has been estimated to be greater than that of diabetes, and similar to that of clinical depression (Ladabaum).

Management of IBS

The etiology of IBS is currently unknown. Because of this, the goal of therapy is symptom management and reduction in the frequency and severity of episodes, or "bouts." The management of IBS ranges from dietary and behavioral changes to medications. Dietary changes may involve slowly increasing fiber while also reducing dairy products, fatty foods, spices and caffeine. Patients are often encouraged to try an exclusion diet - restricting their diet to bland foods, gradually adding new foods, and recording symptoms (John Hopkins). Therapeutic agents, whether prescription or over-the-counter, are utilized primarily for symptom management. The most common prescription therapeutic agents have the greatest impact on bowel function by either slowing down or speeding up transit times. Other forms of therapy have targeted the gut-brain function and involved the use of agents such as antidepressants and even hypnosis.

Probiotics are currently under consideration to help in the management of IBS, as they support a healthy, normal digestive system.

Probiotics defined

Probiotics have been defined as live microbial food supplements which beneficially affect the host by improving the intestinal microbial balance, or, more broadly, as "living micro-organisms, which upon ingestion in certain numbers, exert health affects beyond inherent basic nutrition (Gaurner & Shaafsma). It was Metchnikoff in 1907 who first implied that ingested bacteria, in the form of yogurt and other fermented foods, could beneficially affect the normal gut flora (Metchnikoff).

Many of the probiotic products on the market today contain lactobacilli (a type of lactic acid bacteria), which represents a relatively small proportion of the normal total gut microflora. Lactic acid producing bacteria (LAB) are a group of bacteria that are mostly of human origin, with the various strains differing in their features. All LABs colonize mucosal surfaces, including the intestinal system, and promote vitamin production, natural protection from invading pathogens, and food digestion. Bifidobacteria are one type of lactic acid producing bacteria. They are active in bile acid deconjugation, catabolism of dietary carbohydrates, and synthesis of vitamins (Mombelli and Gismondo).

Probiotics in IBS

A limited amount of data in scientific literature suggests that IBS patients may have an imbalance in their gastrointestinal flora (Balsari). This has been demonstrated through classic microbiology studies using conventional plating techniques as well as molecular approaches. In addition, function studies in IBS patients' flora have shown that IBS patients produce an excessive amount of short-chain volatile fatty acids and hydrogen gas versus healthy controls (Treem, King). Therefore, it would appear plausible that some disturbance in the normal flora among IBS patients may indeed account for the symptoms observed, or, alternatively, that the GI environment in IBS patients provides conditions conducive to the proliferation of a more virulent flora. Recently, the concept of small bowel bacterial overgrowth (SBBO) has been proposed as a plausible explanation for IBS symptoms (pimental, lin) several studies in the scientific literature indicate that SBBO is much more common in IBS subjects. These observations suggest that IBS subjects possess a modified flora both in composition as well as end product metabolism. Therefore, the concept of using a probiotic to help promote normal digestive function is an extremely intriguing approach.

Several studies in scientific literature have explored the use of probiotic therapy for the alleviation of the symptoms of IBS, with mixed results (Nobaek, Halpern, O'Sullivan). The majority of these studies were small and many were poorly controlled, providing a possible explanation for the mixed results. A second possible explanation might be the type of probiotics evaluated in these studies. Certain probiotics have not been demonstrated to possess the ability to alter the composition or metabolism of the colonic flora in a manner that would be beneficial for the IBS patient. Alternatively, various probiotics may not work in conjunction with the normal flora to have the positive impact on the human immune system necessary to alleviate the symptoms. However, recent studies that are much larger and well controlled are beginning to shed new light on probiotic benefits (O'Mahoney, Whorwell).

References

LadabaumU. Irritable Bowel Syndrome. Adv Stud Med 2004; 4(3):128-134

Drossman DA, Camilleri M, Mayer EA, Whitehead WE. AGA Technical Review of Irritable Bowel Syndrome. Gastroenterolgy 2002;123:2108-2131.

Johns Hopkins Resource Center, Digestive Diseases Library. Monograph on Irritable Bowel Syndrome (2004). www.hopkins-gi.org

Guarner F and Schaafsma GJ. Short Communication: Probiotics. Int J Food Microbiol 1998; 39:237-238.

Metchnikoff, E. 1907. The prolongation of life. Optimistic studies. William Heinemann, London, United Kingdom.

Mombelli B and Gismondo MR. The use of probiotics in medical practice. Int J Antimicrobial Agents 2000;16:531-536.

Balsari A, Caccarelli A, Dubini F, Fesce E Poli G. The fecal microbial population in the irritable bowel syndrome. Microbiologica 1982; 5: 185-194.

Treem WR, Ahsan N, Kastoff G, Hyams JS.Fecal Short-Chin Fatty Acids in Patients with Diarrhea Predominant Irritable Bowel Syndrome. J Ped Gastro Nutr 1996;23: 280-286.

King TS, Elia M, Hunter JO. Abnormal colonic fermentation in irritable bowel syndrome. Lancet 1998; 352: 1187-89..

Pimental M, Chow E, Lin H. Normalization of lactulose breath testing correlates with symptom improvement in irritable bowel syndrome: a double-blind, randomized, placebo controlled study. Am J Gastroenterol 2000; 98:412-419.

Lin, HC. Small Intestinal Bacterial Overgrowth. A framework for understanding irritable bowel syndrome. JAMA 2004; 292:852-858.

Nobaek S, Johasson M-L, Molin G, Ahrne S, and Jeppsson B. Alteration of intestinal microflora is associated with reduction in abdominal bloating and pain in patients with irritable bowel syndrome. Am J Gastroenterol 2000;95: 1231-1238.

Halpern GM, Prindiville T, Blankenburg M, Hsia T, and Gershwin ME Treatment of irritable bowel syndrome with lactrol fort: a randomized, double blind, cross over study. Am J Gastroenterol 1996;91: 1579-85.

O'Sullivan MA, O'Morain Bacterial supplementation in the irritable bowel syndrome. Digest Liver Dis 2000;32:294-301.

16 O'Mahony L, McCarthy J, Kelly P, Hurley G, Luo F, O'Sullivan G, Kiely B, Collins JK, Shanahan F, Quigley EMM.Lactobacillus and bifidobacterium in irritable bowel syndrome: symptom responses and relationship to cytokine profiles Gastroenterology 2005;128:541-551.

17. Whorwell et al. DDW, May 2005 (abstract)

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