Most dietary carbohydrates are digested and absorbed in the small bowel. However, fiber carbohydrate and other carbohydrates can be metabolized by the normal flora of the colon. The substrate for bacterial fermentation includes compounds for which small bowel digestive and absorptive mechanisms may, or may not, exist and soluble and some insoluble fiber. Products of fermentation include gases and volatile fatty acids which may be absorbed or nourish the colon mucosa. Total body nutrition and metabolism may also be affected by the products digested and absorbed in the colon.