Fibre, fermentation, flora, and flatus.

Leading articleFibre, fermentation, flora, and flatus Research into flatogenesis has undergone several, apparently unrelated, phases.Early studies of the volume of gas in the gastrointestinal tract'2 were prompted by the abdominal pain and discomfort experienced by sailors and airmen who had been subjected to explosive decompression.The second phase was aided by the realisation that human gas production could pose an explosion hazard during longterm space flight.3Since that time, there has been little attempt to quantitate gas production in man although there have been many studies on concentrations of H2 and CH4 in end expired breath.There have been remarkable advances during the last 15 years in our understanding of the nature of non-absorbed sugars and dietary fibre and of their fermentation in the large intestine.It is now possible to construct a clearer picture of the overall stochiometry of colonic fermentation and gas production in man.The link between large intestine fermentation of non-absorbed carbo- hydrate and gas production has been exploited in numerous breath tests for malabsorption because a portion of the gas produced (H2 and CH4) is absorbed from the lumen of the large intestine into the blood stream and excreted in the lungs.As much as 13% of H2 gas may be lost through this route.4Whilst H2 appears to be the major unique gas produced by intestinal fermentation, a proportion of individuals also excrete appreciable quantities of CH4-"14 In patients with unresected colon cancer the proportion of methane-producers is high (86-92%), falling to normal levels (43-47%) after resection.13 Methanogenic bacteria are also present in large quantities in patients with diverticulosis.1s In contrast with these data, a recent study of South African populations has shown that although there was a wide variation in the proportion of methane producers in different ethnic groups, this did not relate to the relative risk of developing colon cancer.'6The picture is confusing and the report of Weaver and colleagues,'7 in this issue of Gut is therefore timely.In this study, an attempt has been made to determine the stochiometry of fermentation of defined substrates by incubation of faecal samples from a H2 and a CH4 producer.It addresses the essential questions of 'How much ', 'Why?', 'Where?', 'What?', and 'Why not?'.How much?Most studies have measured only the small proportion of H2 and CH4 which is excreted in the breath.Because H2 and CH4 are expressed as concentra- tions, it is not possible to calculate total output unless respiratory volumes are known.End expiratory gas measurements are straightforward in patients or volunteers, but rectal intubation for measurement of flatus volumes is not.A non-invasive alternative to rectal intubation is suggested 6 on