Dietary Fiber consists of nondigestible carbohydrates and lignin that are intrinsic and intact in plants. Functional Fiber consists of isolated, nondigestible carbohydrates that have beneficial physiological effects in humans. Total Fiber is the sum of Dietary Fiber and Functional Fiber. Fibers have different properties that result in different physiological effects. For example, viscous fibers may delay the gastric emptying of ingested foods into the small intestine, resulting in a sensation of fullness, which may contribute to weight control. Delayed gastric emptying may also reduce postprandial blood glucose concentrations and potentially have a beneficial effect on insulin sensitivity. Viscous fibers can interfere with the absorption of dietary fat and cholesterol, as well as with the enterohepatic recirculation of cholesterol and bile acids, which may result in reduced blood cholesterol concentrations.
Consumption of Dietary and certain Functional Fibers, particularly those that are poorly fermented, is known to improve fecal bulk and laxation and ameliorate constipation. The relationship of fiber intake to colon cancer is the subject of ongoing investigation and is currently unresolved. An Adequate Intake (AI) for Total Fiber in foods is set at 38 and 25 g/d for young men and women, respectively, based on the intake level observed to protect against coronary heart disease.
Median intakes of Dietary Fiber ranged from 16.5 to 17.9 g/d for men and 12.1 to 13.8 g/d for women (Appendix Table E-4). There was insufficient evidence to set a Tolerable Upper Intake Level (UL) for Dietary Fiber or Functional Fiber.
Dietary, Functional, and Total Fiber