Because the polymer is so large, it is not absorbed by the intestinal tract. As a result, the polymer remains in the intestine and keeps water with it. The end result is that there is much more water in the stool, keeping it soft, and causing it to move through the intestine more quickly. One of the advantages of Miralax is that it is a tasteless and odorless powder than can be readily mixed into juices or other fluids without altering their taste. In high doses, Miralax often produces diarrhea.
Mineral oil is a non- absorbable oil that is digested by bacteria living in the large intestine.
Some of the by-products of this digestion stimulate the intestine to secrete salt and water. This results in there being much more water in the stool, keeping it very soft, and causing it to move through the intestine more quickly. When taking high doses of mineral oil, many children will experience some orange seepage as well as some itching at their anus. Fiber laxatives contain complex sugars that are not digested or absorbed in the intestine. As a result, the sugars remain in the intestine and keep water with them.