Suggested Citation: Garko, M.G. (2013, September). Fiber – Part III: Overview of scientifically supported health and wellness benefits of dietary and functional fiber. Health and Wellness Monthly. Retrieved (insert month, day, year), from www.letstalknutrition.com.
Fiber – Part III: Overview of Scientifically Supported Health and
Wellness Benefits of Dietary and Functional Fiber
Michael Garko, Ph.D.
Producer and Host of Let’s Talk Nutrition
It is commonly recognized that there is an inadequate intake of dietary fiber in the day-to-day diets of the general population (i.e., children, adolescents and adults) in the United States. Over the past 20 years data has emerged from two different National Health and Nutrition Examination Surveys revealing that from 1988-1991 the average/mean daily intake of dietary fiber was approximately 14.82 grams (see Alaimo et al., 1994) and from 1999-2008 the average/mean daily intake of dietary fiber was approximately 15.78 grams (see King et al., 2012).
The recommended daily intakes of the U.S. Department of Agriculture and U.S. Department of Health and Human Services (2010, December), Centers for Disease Control and Prevention (2013), National Cancer Institute (2011) or Institute of Medicine (2005) range from 19 grams a day (children 1-3 years of age) to 38 grams (men 19-50 years of age). Another frequently cited recommendation is 14 grams per 1,000 calories. Hence, it is more than apparent that Americans do not consume a sufficient amount of dietary and functional fiber.
This inadequate consumption of dietary and functional fiber is real and measurable to the extent that it is contributing to the ill health of tens of millions of Americans. Findings from observational, epidemiological, experimental and clinical studies have established an association between an inadequate intake of fiber and coronary heart disease, stroke, type 2 diabetes, obesity, insulin resistance, high blood pressure, high cholesterol, along with gastrointestinal diseases and disorders such as diverticulosis, irritable bowel syndrome (IBS), leaky gut syndrome, Candida Albicans, gallstones and colon cancer, among other diseases and conditions. Stated another way, there is a robust body of research spanning over several decades to support the assertion that diets high in dietary and functional fiber help prevent and treat chronic diseases and contribute to metabolic, cardiovascular, gastrointestinal, endocrine and immune health, among other health benefits (e.g., see Anderson, et al., 2009; Bijkerk et al., 2004; Buttriss & Stokes, 2008; Cho & Dreher, 2001; Institute of Medicine, 2002, Lattimer & Haub, 2010; Lyon, 2012; Park et al, 2011; Park et al., 2009; Sanchez-Muniz, 2012; Slavin, 2013)..
The September, 2013, issue of Health and Wellness Monthly is an overview of scientifically supported health benefits of dietary and functional fiber in either preventing or treating chronic diseases. Its purpose is to provide a general sketch of the ways in which dietary and functional fiber can contribute to health, wellness and wellbeing. Upcoming issues will focus on the ways in which different types dietary and functional fibers can help address particular health concerns such as overweight and obesity, cardiovascular disease (e.g., hyperlipidemia, hypertension, stroke, coronary heart disease), cancer (e.g., colorectal cancer, breast cancer), type 2 diabetes mellitus, gastrointestinal-related diseases and disorders (e.g., irritable bowel syndrome, diverticular disease, constipation, etc.) and immune dysfunction.
Definition of Dietary and Functional Fiber
In the July, 2013, issue of Health and Wellness Monthly focus was put on the conceptual confusion and controversy surrounding the effort since the 1950s to define dietary fiber and what sort of definition would be useful not only for the scientific community but also for laypeople.
An array of definitions were presented and discussed. One of the conclusions reached was that the approach of the Institute of Medicine (IOM) in defining fiber was useful because it (a) recognizes different sources, types and components of fiber, (b) includes isolated or extracted nondigestible carbohydrates using chemical, enzymatic, or aqueous procedures and (c) includes beneficial physiological/health effects for humans in its definition (see Garko, 2013).
Institute of Medicine’s Definition
At its most fundamental macronutrient level, food fiber is a carbohydrate. Recognizing that a diversity of carbohydrates (i.e., plant cell wall and storage carbohydrates, carbohydrates from animal foods, naturally occurring or synthesized/manufactured isolated and low molecular weight carbohydrates) constitute the human diet and resist digestion in the small intestine and arriving in the colon/large intestine relatively intact, the Institute of Medicine (2005) adopted the following two-pronged approach to define edible, nondigestible carbohydrates:
- 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 (Institute of Medicine, 2005, p. 340).
Distinguishing characteristics of dietary fiber. Following the IOM, the following are some of the more distinguishing features of dietary fiber:
- Consists of nondigestible food plant carbohydrates and lignin
- Made-up primarily of a mixture of polysaccharides, which are integral elements of the plant’s cell wall or intercellular structure
- Includes oligosaccharides and resistant starch
- Not digested and absorbed in the human small intestine
- Physicochemical properties stem from the three-dimensional plant matrix which remains basically intact
- Contains other macronutrients (e.g., digestible carbohydrate and protein) normally found in foods (Institute of Medicine, 2005).
Distinguishing characteristics of functional fiber. According to the IOM, the following are some of the more distinguishing features of functional fiber:
- Consists of isolated or extracted nondigestible carbohydrates
- Chemical, enzymatic, or aqueous procedures used to isolate or extract nondigestible carbohydrates
- Confers beneficial physiological effects in humans
- Consists of synthetically manufactured and naturally occurring isolated oligosaccharides
- Consists of manufactured resistant starch
- Consists of naturally occurring polysaccharides and oligosaccharides extracted from their plant source and modified (e.g., to a shorter polymer length or to a different molecular arrangement)
- Consists of isolated, manufactured, or synthetic oligosaccharides of three or more degrees of polymerization
- Consists of animal-derived, nondigestible carbohydrates (Institute of Medicine, 2005, p. 340).
Sketch of Health Benefits of Dietary and Functional Fiber
The modern era of research into a fiber and its contribution to health and wellness began in the 1950s (Dreher, 2001). However, it was not until the beginning in the 1970s, when researchers began in earnest to study the health benefits of dietary fiber. As Spiller et al. (1978) have described it, back then there was a transition from viewing dietary fiber as a hypothesis or fad without much scientific proof to recognizing it a legitimate health concept of nutritional sciences. There was an improvement in the scientific quality of studies and greater use of better analytical methodologies to determine the health benefits of dietary fiber (see Spiller et al, 1978).
FDA Approved Health Claims
Over the subsequent decades, observational, epidemiological, experimental and clinical studies have served to establish dietary and functional fiber as important and necessary in helping to create, sustain and reclaim health. As a result of this research, the U.S. Food and Drug Administration (FDA) has issued two health claims associated with the consumption of fiber.
The first claim features the consumption of fiber and cancer and states that “[l]ow fat diets rich in fiber-containing grain products, fruits, and vegetables may reduce the risk of some types of cancer, a disease associated with many factors” (U.S. Food and Drug Administration, 2013, p. 1).
The second claim involves fiber-containing foods and coronary heart disease (CHD) and states that “[d]iets low in saturated fat and cholesterol and rich in fruits, vegetables, and grain products that contain some types of dietary fiber, particularly soluble fiber, may reduce the risk of heart disease, a disease associated with many factors” (U.S. Food and Drug Administration, 2013, p. 1).