Inulin

Not exactly, but inulin belongs to the same fiber family as FOS.

Inulin is a soluble, fermentable fiber made mostly from chicory root. Cats cannot digest it, so it passes to the large intestine, where bacteria ferment it into short-chain fatty acids. AAFCO lists inulin among the pet food ingredients that often supply dietary fiber. For a cat with a digestive or other medical condition, ask your veterinarian about fiber in the diet.

Source: aafco.org

Inulin is added as a prebiotic, a fiber that feeds gut bacteria. Tufts veterinary nutritionists name inulin, with guar gum, among the common soluble fiber sources in pet foods, and they explain that fermentable, soluble fibers are often called prebiotic. In cat food it is used in small amounts and can affect stool quality and regularity.

Source: sites.tufts.edu

There is little cat-specific evidence for that. Inulin is a soluble fiber, and soluble fibers pull water into the gut, which can soften stool. Most published feeding work on constipation in cats has looked at psyllium, not inulin. A constipated cat needs a veterinarian to find the cause, since diet is only one possible factor.

Large amounts of fermentable fiber can loosen stool or cause gas, because bacteria ferment it quickly and the colon holds more water. Tufts veterinary nutritionists note that too much highly fermentable fiber can interfere with digestion. The inulin in commercial dry food is usually a small amount listed near the end of the ingredients. A cat with ongoing diarrhea should see a veterinarian.

Source: sites.tufts.edu

Pettings gives inulin 4 out of 5 and lists it as a prebiotic fiber. It appears on 9 of the 149 dry cat foods we list. Cats cannot digest it, so it feeds gut bacteria that produce short-chain fatty acids. Each food's page shows how it scores overall.