Inhibitory actions of a high fibre diet on intestinal gas transit in healthy volunteers

Background: Fibre treatment often produces gaseous symptoms which have been attributed to fermentation by colonic bacteria with increased gas production. Effects of fibre ingestion on intestinal gas flow are unexplored. Aims: We aimed to test the hypothesis that consumption of a high fibre diet retards gas transit. Subjects: Ten healthy volunteers participated. Methods: To investigate the effects of fibre on gas dynamics, physiological gas mixtures were jejunally perfused at 12 ml/min x 2 hours after a standard diet for seven days with and without psyllium 30 g/day in a crossover fashion. Gas was collected from an intrarectal catheter to bypass the anus and evacuation was quantified in real time using a barostat. Results: On initiating gas perfusion under control conditions, an initial lag phase with no gas expulsion was observed ( 1129 ( 274) seconds). Thereafter, gas evacuation from the rectum proceeded with cumulative volumes of 1429 ( 108) ml by the end of the second hour. Evacuation was pulsatile with passage of 20.9 (2.5) boluses, with mean volumes of 68.2 (5.0) ml. Fibre prolonged the lag time ( 2265 (304) seconds; p< 0.05) and reduced cumulative gas evacuation volumes (1022 (80) ml; p< 0.05). Decreased gas evacuation resulted from reductions in the numbers of bolus passages (14.2 (1.1); p< 0.05) but not bolus volumes (70.7 (3.4) ml; p = 0.66). Conclusions: Consumption of a high fibre diet retards intestinal gas transit by decreasing bolus propulsion to the rectum. Thus, in addition to increasing gas production by colonic flora, fibre ingestion may elicit gaseous symptoms by promoting gas retention.