To study the intracolonic digestion of starch, 5 healthy volunteers were maintained on a constant diet for 7 days. On the fourth day, the cecum was intubated and a suspension of raw wheat starch (50 g, in 500 ml of 154 mM NaCl and containing 10 g of polyethylene glycol 4000) was infused into the distal ileum at 2 ml/min. Hydrogen excretion in breath was measured, cecal contents were sampled, and symptoms were recorded. For the 2-3 days before and after starch infusions, fecal weight, pH, and percentage of dry matter were monitored; fecal outputs of starch, volatile fatty acids, lactic acid, ethanol, polyethylene glycol, alpha-amylase, nitrogen, and ammonia were also measured. A lactulose (10 g) hydrogen breath test was performed 5-7 days after the starch infusions. After the infusion of starch, concentrations of lactic and volatile fatty acids increased and pH decreased markedly in cecal contents. None of the fecal values changed significantly after starch, however, indicating that carbohydrate catabolism was nearly complete and that the colon absorbed the catabolic products efficiently. Abdominal symptoms, especially bloating, were noted by all subjects, and 2 subjects complained of cramping pain. No subject experienced diarrhea. The amounts of starch metabolized in the colon (47.3 +/- 2.9 g), as calculated from the excretion of H2 in breath compared to the hydrogen breath test after lactulose, were close to the actual load (50 g).