An excess of water keeps the feces soft, and that is very important in the obese, who commonly suffer from constipation and a spastic colon. While a patient is under treatment we never permit the use of any kind of laxative taken by mouth. We explain that owing to the restricted diet it is perfectly satisfactory and normal to have an evacuation of the bowel only once every three to four days and that, provided plenty of fluids are taken, this never leads to any disturbance. Only in those patients who begin to fret after four days do we allow the use of a suppository. Patients who observe this rule find that after treatment they have a perfectly normal bowel action and this delights many of them almost as much as their loss of weight.
Source: Pounds and Inches by Dr. ATW Simeons, award-winning endocrinologist