I find the term ‘prebiotics’ to be a bit misleading. Since the term ‘Probiotics’ refers to the beneficial bacteria that live in the intestines, it is natural to assume that the term prebiotics refers to a precursor of the bacteria. It doesn’t. The term prebiotics refers to a special type of fiber that can be broken down for energy by the bacteria that live in the gut. Here is the best description I found written by Elizabeth Warren. Probiotics “contribute to a healthy environment for gut flora, usually by providing sources of fermentable foods which bacteria can digest. Nutrients released feed both the beneficial bacteria and cells of the colon, improving the environment and immune function of the large intestine.”
Fiber is divided into two categories, insoluble which passes through the intestines virtually unchanged and soluble which is metabolized by bacteria for food. The soluble fiber must pass through the acidic environment of the stomach intact. When it reaches the intestines, the normal resident bacteria digest it for food. Maintaining a healthy population of non-pathogenic bacteria keeps the harmful bacteria from invading the gut and causing disease. The byproducts also decrease the pH of the colon as well as stimulate absorption of sodium and water.
There are basically two types of insoluble fiber that work well dogs and cats, oligofructose and inulin. Oligofrutose is found in soybeans, oats, beets and tomatoes while inulin is found in Jerusalem artichoke, jimcama and chickory root.
Sources:
-Kirk, C. Top Neutraceuticals in Pet Foods and Practice, World Small ANimal Veterinary Association World Congress Proceedings 2011.
-Pan, X et al., Prebiotics oligosaccharide change the concentrations of short-chain fatty acids and the microbial population of mouse bowel. J of Zhejiang Immuno Source B 2009; 10(4): 258-263.
-Warren, E. Nutraceuticals, VIN, April 4, 2007.
-Wontinger, A. What Do Prebiotics and Probiotics Really Do? Western Veterinary Conference 2012.