What is Dietary Fiber?
As noted by the European Food Safety Authority [EFSA 2009], the interest in defining and quantifying dietary fiber in foods lies in the physiological effects that are associated with their consumption, which include decreased intestinal transit time and increased stool bulk, reducing blood total and/or LDL cholesterol concentrations, and reducing post-prandial blood glucose and/or insulin concentrations, among others.
The key characteristic of dietary fibers is that they are not hydrolyzed by the enzymes in the small intestine and therefore escape digestion and absorption. Dietary fibers comprise a variety of substances that may differ in their chemical and physical properties and exert different types of physiological effects. Although a number of physiological effects have been traditionally linked to dietary fibers in general, as scientific knowledge has increased other beneficial effects have emerged; for example, effects such as the production of specific short chain fatty acids through selective colonic fermentation, stimulation of bifidobacteria growth, increased calcium absorption, increased insulin sensitivity and modulation of satiety have been discovered to be related to certain types of dietary fiber.
Although most fibers will produce more than one of these physiological effects, no one fiber produces all. Some effects are well recognized for a large number of different fiber types, while others can be very fiber specific. Thus, it is important to consume a variety of fibers for their unique effects for maximized health.
These physiological effects, rather than a specific chemical composition or source, are key elements of the health benefits of dietary fiber. Therefore, appropriate definitions of dietary fiber are based on the presence of beneficial physiological properties, without differentiation between dietary fibers that are extracted or isolated from an agricultural source, synthesized, or present in an agricultural commodity.
Through the increased emphasis on the need to increase fiber intake, the food industry has developed fibers that can be added to foods and beverages. A growing number of products – ranging from cereals and breads to fruit juices and yogurts and milk – now contain added fiber.