Dietary fiber: The prebiotic connection
Dietary fiber: the prebiotic connection
Where does dietary fiber occur in food and supplements?
Fiber-containing foods include whole grains, vegetables, fruit, beans, nuts, and seeds. Individuals eating a healthy vegetarian diet may consume more than 50 g of dietary fiber per day. There is no upper limit (UL) for fiber consumption set by the Institute of Medicine (IOM). The 2010 Dietary Guidelines for Americans (DGA) recognized fiber as a "nutrient of concern" in the U.S. diet.
Most foods are low in fiber, with fruit and vegetable servings containing about 1 to 3 g of fiber per serving. Servings of whole grains also contain no more than 3 g of dietary fiber, while legumes may contain up to 6 g of fiber per serving. Thus, for most consumers, additional sources of fiber are needed to consume the recommended intake.
In addition, fibers have been divided into soluble and insoluble fiber. Listing of insoluble and soluble fiber is voluntary on the label. It was previously thought that solubility of fiber would predict physiological effects. Soluble fiber was believed to be associated with cholesterol-lowering and improved glucose response, while insoluble fiber was associated with improved laxation. Although there may be some truth to these generalizations, many soluble fibers do not lower serum lipids, and soluble fibers can improve gut health.
Nutrition Facts panels must include information on the fiber content of foods. Because fiber is a shortfall nutrient, many food manufacturers include additional fiber in foods and beverages. Thus, some cereals contain as many as 13 g of dietary fiber per serving, and some chocolate bars may contain 9 g of dietary fiber per serving.
A wide range of fibers is added to foods or consumed as supplements. Oat bran, barley bran, and psyllium have approved health claims in the United States for their ability to lower blood lipids. Other popular fibers include polydextrose, resistant maltodextrin, wheat bran, soluble corn fiber, partially hydrolyzed guar gum, pea hull fiber, glucomannan, psyllium, inulin, and other oligosaccharides.
Proposed guidelines from the FDA will require that isolated fibers show a physiological effect before they can be deemed dietary fiber. Currently, any compound that is regarded as dietary fiber by accepted chemical methods can be added to foods and beverages and counted as a fiber source on the Nutrition Facts panel.