It's indigestible fiber and my vet said it would be fine to add to their food (1-4 grams per day) to aid with constipation. It bulks up the stool and draws water into the colon, hence making for softer stools that are easier to pass. I think the idea with adding it to raw food diets is just to add some fiber as some cats get constipated without it. It's very important that the cat drinks enough or gets wet food with it and it may cause flatulence.