Only Citrucel? has SmartFiber?. SmartFiber is derived from cellulose which occurs naturally in plants and is the most abundant, renewable fiber on earth. With nature at it's core, Citrucel with SmartFiber is designed to be less harsh on your system. And SmartFiber is smart - because it works. Citrucel with SmartFiber is proven to help restore and maintain regularity. Citrucel with SmartFiber is 0% fermentable, so unlike psyllium, SmartFiber can not, will not cause excess gas or bloating, is non-allergenic and gluten free. Now that's Smart Fiber! Doctor recommended. No gritty texture. Easy mixing. Daily source of 100% soluble fiber. For relief of constipation. This product helps restore and maintain regularity. Also useful in the treatment of constipation associated with other bowel disorders when recommended by a physician.