The ENTIRE article is good. The following just caught my attention...
Pumpkin. By far one of the most popular remedies for constipation in cats by veterinarians and owners alike is inclusion of pure canned pumpkin to the diet. Results are mixed. According to data by the USDA, canned pumpkin is 90% moisture and 2.8% fiber. That means that with each tablespoon of canned pumpkin mixed into a portion of cat food, mostly water and little fiber is added. This means that canned pumpkin is not a stool bulker, but must have other laxative effects. I have heard that canned pumpkin has short-lived effects, however. Cats appear to get accustomed to it, and feces return to being small, dry, and infrequent. Although canned pumpkin is accepted by many cats, some cats will not eat food in which it was included.
http://feline-nutrition.org/health/constipation-real-help-for-your-cat