Because of its high amount of fiber, prune juice works as a laxative. Prune juice also contains a chemical called sorbitol that works to soften stools, making them easier to pass.
Sorbitol works because the body does not digest it easily, which requires the body to add water to it and make the stool bulkier. To reap the benefits of prune juice, a person should drink two 8-ounce glasses a day. The best time to drink prune juice is in the morning and at night. If the second serving of prune juice is consumed too soon after the first serving, the person could get diarrhea.