Diet and Irritable Bowel Syndrome

Bacterial Flora and Pro/Prebiotics

Some patients with IBS, estimated at between 4 and 26%, will develop the disorder after an episode of acute gastroenteritis, although such patients characteristically have only diarrhea without constipation.[24] The reasons for this association are not clearly defined, and the occurrence of other life stresses or other potentially confounding concurrent etiological factors have not been systematically examined. When they are, the postinfectious group are found to have more of them.[24*,25*] The association with intestinal infection, however, raises the possibility that some interaction between the intestinal bacteria and the intestine itself may be altered. There is evidence from germ-free animals that motor and sensory function mediated by the enteric nervous system is altered, and can be corrected by the addition of bacteria.[26*] Moreover, changes in motility occur in patients with small intestinal bacterial overgrowth (SIBO).[26*] A randomized trial of neomycin in IBS patients produced more symptom improvement than in controls, especially in those patients whose lactulose breath test had normalized, consistent with elimination of SIBO.[27] Moreover, the lactulose breath test was abnormal in patients with fibromyalgia, a condition often occurring with IBS.[28*]

Many factors are thought to be important in altering bacterial flora in the human intestine, including stress, diet, and antibiotics.[29*] Because flora are indeed altered in IBS, trials of various probiotic organisms have been attempted to alleviate symptoms. Of eight controlled trials, six showed some evidence of benefit, with five using only a single organism.[30*] The total number of patients treated (265 total) is small, however. One study tested two individual organisms in 77 patients, and the bifidobacterium strain, in contrast with the lactobacillus organism, provided benefit on pain and bloating.[31**] The benefit was suggested to be due to alteration in cytokine production, but was only modest. Quality of life measures were minimally affected. Diet type (Western, Japanese, Indian, etc.) can affect human gut microflora, but bifidobacteria are not the most affected by these various diets that reflect differences in IBS prevalence.[29*]

The hypothesis that symptoms in IBS may be due to changes in cytokine production from the intestine is intriguing. Cytokines can produce many of the nongastrointestinal symptoms seen in IBS (e.g. fatigue, nausea), and have been implicated in depression, a condition that is present in many IBS patients.[32] More data are needed to determine whether cytokines are implicated in IBS symptomatology and, if so, whether bacterial profile or SIBO are factors in producing those symptoms.  Printer- Friendly Email This

Curr Opin Gastroenterol.  2006;22(2):136-139.  ©2006 Lippincott Williams & Wilkins
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