Glucose is a simple sugar that is a constituent of many different types of complex carbohydrates in its ring structural form. Polymers of glucose, like cellulose, are completely insoluble and indigestible. Other polymers, such as starch, are broken down by the enzyme amylase in saliva, and the glucose can then be burned for energy by the body. There are other polymers of glucose, classified as soluble fiber, that are indigestible, but can be broken down by intestinal bacteria to produce short-chain fatty acids.
Insoluble fiber just provides bulk, whereas soluble fiber serves important nutritional functions, such as lowering cholesterol by binding to bile secretions and facilitating their excretion in the feces. Soluble fiber also promotes growth of intestinal probiotic bacteria that produce some vitamins and help to maintain regularity. Insoluble fiber has no calories, and soluble fiber has about half of the calories of simple carbohydrates because it is not completely digested by colonic bacteria.
Many food fillers are derivatives of starch. Maltodextrin is a partially hydrolyzed starch frequently used as a bulking agent in sugar substitutes, but it is metabolized like a sugar. Manufacturers have started using resistant starch and soluble fiber derived from corn as filling agents in an attempt to produce lower calorie products. Resistant starch is starch that is not digested in the small intestine and is considered a different type of dietary fiber, as it can deliver some of the bulking benefits of insoluble fiber and some of the benefits of soluble fiber.
 Brighenti, Furio et al. “Colonic fermentation of indigestible carbohydrates contributes to the second-meal effect.” American Journal of Clinical Nutrition 83.4 (2006): 817-822.
 Englyst, Klaus and Englyst, Hans. “Carbohydrate Bioavailability.” British Journal of Nutrition 94 (2005): 1-11.