The study below found that a STAGGERING 93% of IBS sufferers had sugar malabsorption, and sugar malabsorption contributed to symptoms.

METHODS: A cohort of 239 patients defined as functional bowel complaints was divided into a group of 94 patients who met the Rome criteria for irritable bowel syndrome and a second group of 145 patients who did not fulfill these criteria and were defined as functional complaints. Lactose (18 g), fructose (25 g) and a mixture of fructose (25 g) plus sorbitol (5 g) solutions were administered at weekly intervals. End-expiratory hydrogen and methane breath samples were collected at 30 minute intervals for 4 hours. Incomplete absorption was defined as an increment in breath hydrogen of at least 20 ppm, or its equivalent in methane of at least 5 ppm. All patients received a diet without the offending sugar(s) for one month.

RESULTS: Only 7% of patients with IBS and 8% of patients with FC absorbed all three sugars normally. The frequency of isolated lactose malabsorption was 16% and 12% respectively. The association of lactose and fructose-sorbitol malabsorption occurred in 61% of both patient groups. The frequency of sugar malabsorption among patients in both groups was 78% for lactose malabsorption (IBS 82%, FC 75%), 44% for fructose malabsorption and 73% for fructose-sorbitol malabsorption (IBS 70%, FC 75%). A marked improvement occurred in 56% of IBS and 60% of FC patients following dietary restriction. The number of symptoms decreased significantly in both groups (P < 0.01) and correlated with the improvement index (IBS P < 0.05, FC P < 0.025).

CONCLUSIONS: Combined sugar malabsorption patterns are common in functional bowel disorders and may contribute to symptomatology in most patients. Dietary restriction of the offending sugar(s) should be implemented before the institution of drug therapy.
Source: http://www.ncbi.nlm.nih.gov/pubmed/10979349

And the review below asks: “is irritable bowel syndrome a low-grade inflammatory bowel disease?”

Irritable Bowel Syndrome (IBS) is multifactorial in its etiology and heterogeneous in its clinical presentation and pathogenesis. It is recognized that inflammation plays an important role in symptom generation, at least in a subset of patients with IBS. Previous gastroenteritis has been identified as the most important risk factor for IBS, and several studies reported that a substantial proportion of patients with gastrointestinal infection develops IBS symptoms,which can persist for several years. Recent studies have demonstrated that a proportion of IBS patients without any history of enteritis has signs of immune activation in the gut. There is clinical overlap between IBS and inflammatory bowel disease (IBD), with IBS-like symptoms frequently reported in patients before the diagnosis of IBD, and a higher than expected percentage reports of IBS symptoms in patients in remission from established IBD.
Source: http://www.ncbi.nlm.nih.gov/pubmed/15862932?dopt=Citation

So, considering the above two studies, what could cause sugar malabsorption and inflammation in the guts of IBS sufferers? Perhaps the answer is a bug called MAP!