Milk is a useful test meal for measurement of small bowel transit time.

To improve and standardize the measurement of small bowel transit time, milk was employed for the test meal instead of the conventional lactulose meal. Although 92% of the subjects were lactase deficient, only 2% were milk intolerant and 13% were lactose intolerant. Small bowel transit time with milk (milk breath hydrogen test) was 113 +/- 9 min (mean +/- SE, n = 20); the normal range calculated from the mean +/- 2 SD was 31-195 min. The coefficient of variation in the milk hydrogen breath test was 13 +/- 4% (n = 6), whereas in the lactulose hydrogen breath test, it was 39 +/- 16% (n = 10). The frequency of non-hydrogen producers, the occurrence of discomfort, and the reproducibility were better, though not significantly so, in the milk hydrogen breath test than in the lactulose. Since lactase activity in the intestine is variable in lactase-deficient subjects, small bowel transit times for milk may change from subject to subject. However, individual reproducibility of the milk hydrogen breath test is good. It could be useful for pharmacological experiments using paired comparison, for screening tests, or for the follow up of diseases in which small bowel transit time is affected.