Does gender or the menstrual cycle affect colonic transit?

Controversy exists as to whether slowing of colonic transit occurs in the high progesterone luteal phase of the menstrual cycle. To clarify this issue, colonic transit studies using radiopaque markers were performed on 10 women in the follicular phase, 10 women in the luteal phase of the menstrual cycle, and five women on oral contraceptives, and the results were compared with transit times in 11 male controls. No significant differences in colonic transit were found between either phase of the menstrual cycle. Colonic transit in women was slower than in men, but this was not statistically significant. In the clinical setting, therefore, colonic transit studies can be performed throughout the menstrual cycle or when taking oral contraceptives. In addition, a single standard for normal values can be used for both men and women.