The effectiveness of prunes as a laxative is related to their high sorbitol, diphenylisatin and fiber content. Sorbitol draws water into the large intestine, which stimulates bowel function. Diphenylisatin and fiber are both natural laxatives, which contribute to bowel function.
Prunes or prune juice should be used sparingly, and it is recommended that elderly people consult a doctor before using prune juice as a laxative. The reason for this is that sorbitol in large amounts causes diarrhea. One prune contains over 1/2 gram of fiber and 1 gram of sorbitol. Many stone fruits, such as cherries, peaches and plums, also contain sorbitol.