Generally, fiber is a type of complex carbohydrate or long chain of sugar molecules arranged in a special way to make them inaccessible to human enzymes. Enzymes are substances which facilitate chemical reactions in the body.
Fibers can be intrinsic and intact in plants, or in some cases, isolated, extracted or manufactured. There are several different types of fiber characterized by differences in solubility, viscosity and fermentability. Differences in these characteristics impact the effects fiber has in the body.
Insoluble fibers tend to add roughage to the diet to help speed up the removal of waste from the digestive system. Very viscous soluble fibers thicken when mixed with fluids and tend to slow digestion for more balanced nutrient absorption. Only fermentable fibers can serve as food for the friendly bacteria residing in the GI tract, also referred to as the gut microbiome.
In order to get all of the various benefits of fiber, it is important to eat a wide variety of fiber-rich foods.