Dietary Fiber: A New Beginning?

December 2001

The subject of dietary fiber seems to have taken a back seat over the last five to seven years in the mind of the consumer, yielding the floor to a succession of more trendy issues. To many, the term still conjures up memories of “oat-bran everything” — with little hope of palatability. This has slowed consumer interest, which is unfortunate because most people don’t get enough dietary fiber. Whereas the National Academy of Science (NAS) Committee on Dietary Fiber recommends a Daily Value of 25 grams, U.S. consumers average only 14 to 15 grams per day. D

In “Dietary Fiber: A Healthy Discussion,” in the January 1999 issue of Food Product Design, Guy Crosby, vice president, Opta Food Ingredients, Bedford, MA, said, “Some of the hurdles facing food formulators are cost and FDA limits on labeling the benefits. Without the ability to promote the healthy benefits through labeling, there is little justification to increase the cost of a formulated food by adding more fiber. Consumer education on the benefits of fiber is also critical to justifying the cost of adding fiber to food, or demanding foods with more fiber.” This accurately states the dilemma, and not much has changed in the two years since that article, although the fiber product landscape has continued to change.

Fiber may have fallen off the consumer scope, but the ingredient and nutritional communities are working to increase its visibility. The market is in a redefinition phase, with a broader acceptance of what is considered a dietary fiber. Some products have disappeared, others have merged forces, and there has been increased focus on clinical trials to support claims. Effort also has been placed on delivering a higher percent total dietary fiber (TDF) with more acceptable palatability.

Defining moments
The definition of “dietary fiber” is still in debate. In November 1998, the American Association of Cereal Chemists (AACC) appointed a Dietary Fiber Definition Committee to review and update the definition. This review included an assessment of current analytical methodology so that recommendations could be submitted if improvements were needed. This committee literally “opened up the floor,” asking for input and discussion through an international website, workshops and public forums.

Going into this discussion, the working definition of dietary fiber had been that “dietary fiber consists of the remnants of edible plant cells, polysaccharides, lignin and associated substances resistant to (hydrolysis) digestion by the alimentary enzymes of humans.” This was considered to include cellulose, hemicellulose, lignin, gums, modified celluloses, mucilages, oligosaccharides, pectins, waxes, cutin and suberin. The regulatory definition of dietary fiber for labeling purposes has been limited to its basis in methodology — the fiber must be enzymatically nondigestible and insoluble in four parts ethanol and one part water. This methodology excluded nondigestible water-soluble oligo- and polysaccharides, including fructans and polydextrose. The scientific community agreed that “dietary fiber” should be a term that reflects not only chemistry, but physiological effect as well.

The AACC Dietary Fiber Definition Committee submitted its report Jan. 10, 2001, detailing a new definition: “Dietary fiber is the edible parts of plants or analogous carbohydrates that are resistant to digestion and absorption in the human small intestine with complete or partial fermentation in the large intestine. Dietary fiber includes polysaccharides, oligosaccharides, lignin and associated plant substances. Dietary fibers promote beneficial physiological effects, including laxation and/or blood cholesterol attenuation and/or blood glucose attenuation.”

This new definition offered by AACC would seek to include:
• Non-starch polysaccharides and resistant oligosaccharides. Includes cellulose, hemicellulose, polyfructoses (inulin, oligofructans), gums, galactooligosaccharides, mucilages and pectins.
• Analogous carbohydrates. Includes indigestible dextrins (resistant maltodextrins and potato dextrins–), synthesized carbohydrates (polydextrose, methylcellulose, hydrozypropylmethyl cellulose) and resistant starches.
• Lignin.
• Waxes, phytate, cutin, saponins, suberin, and tannins.
Naturally, additional methods would be needed to encompass this wider definition of dietary fiber.

The Food and Nutrition Board (FNB), through its Dietary Reference Intake (DRI) Committee convened a panel on the Definition of Dietary Fiber, which concluded and reported its findings on April 3, 2001. This panel has proposed three definitions for fiber:
Dietary fiber. Nondigestible carbohydrates and lignin that are intrinsic and intact in plants.
Added fiber. Isolated, nondigestible carbohydrates that have beneficial physiological effects in humans.
Total fiber. Dietary fiber plus added fiber.

The AACC has submitted comments to NAS, and this is still in the comment period. A final definition will be included in the new Dietary Reference Intakes report on macronutrients, which will include an evaluation of dietary fiber and its role in health. These DRI reports were initially projected to be published this year (2001).

Soluble fiber’s new look
With the definition (or definitions) of fiber relatively close to a new resolution, we can discuss several of the products which would be viewed as “dietary fiber” or “added fiber,” depending on the definition adopted. These were topics of discussion in two timely symposia at the AACC Annual Meeting Oct. 14-18, 2001 in Charlotte, NC. One, “Soluble Fiber — A Sticky Problem or a Concept That Has Gelled?” focused directly on soluble fibers, their physiological effects, requirements for health claims and development of new sources. In addition, the Carbohydrate and Nutrition Divisions Joint Symposium presented two sessions on resistant starch — one on development and the second on health-promoting properties, giving a closer look at an emerging, yet not new, fiber ingredient.

Resistant starches (RS) are starches that are not absorbed in the small intestine, but are instead fermented in the large intestine. Three defined types of RS exist. RS1 is starch physically trapped within food — amylolytic enzymes have no effect on this type because the enzymes literally cannot reach them. RS1 starch would fall under the NAS definition of “dietary fiber.” The next type, RS2, also falls under this classification. Enzymes will not affect this native granular starch until it gelatinizes. RS2 can be found in some fruits and vegetables, or may be derived from certain high-amylose starches. RS3 starch is nongranular starch that has been retrograded or is crystalline in structure.

In the human digestive system, resistant starch behaves similarly to conventional insoluble cellulose fibers in that it contributes significantly to fecal bulk and butyrate production, leading to better gastrointestinal health. RS2 starches have been developed with a total dietary fiber content of about 40%, and can be labeled as “cornstarch.” Because these starches have a small particle size, are bland in flavor, are white in color, and absorb less water than many other fibers, they can be formulated into many baked products at significant fiber levels with more-positive textural effects than other fibers.

Studies conducted by National Starch & Chemical Co., Bridgewater, NJ, and American Institute of Baking, Manhattan, KS, showed that an RS2 starch could fortify breads at levels up to 5 grams fiber per 50-gram serving (10% TDF), either alone or in combination with oat fiber. High-fiber breads, crackers and muffins were formulated using RS2 starches. Because these RS products do not significantly swell or interact with other ingredients, they can contribute significant bulk to a formulation with good toleration — previously, high-amylose starches had been used in some reduced fat formulations for much the same purpose.

Polydextrose has been recognized for years as a 1 kcal/gram carbohydrate, used as a bulking agent and sugar-and-fat replacer in confectioneries, dairy products and baked goods. Polydextrose is a randomly branched polysaccharide with a complexity of structure resistant to digestive enzymes. The average degree of polymerization (DP) of polydextrose is stated as 12, with an average molecular weight (MW) of 2,000 (range MW is 162 to 20,000). Polydextrose is considered to be a resistant oligosaccharide (RO), and is already considered to be a dietary fiber in many countries. Under the proposed definitions, it would be regarded as either “dietary fiber” or “added fiber.”

According to Julian Stowell marketing director, Danisco Sweeteners, Ardsley, NY, “Polydextrose is well established as the preferred source of soluble dietary fiber in a growing number of markets around the world. Japan took the lead back in the 1980s and consumers there now enjoy many options for improving gut health.” Polydextrose is sugar-free and safe for diabetics, does not promote tooth decay, and has been shown to increase beneficial microflora in the lower intestine while decreasing the amount of detrimental microflora.

Stowell notes that “current specifications for polydextrose in the Food Chemicals Codex state that polydextrose can contain up to 4% moisture and 6% monomers (glucose, anhydroglucose and sorbitol) — the remaining 90% can be considered fiber.” Further supporting evidence of polydextrose’s fiber role is found in the fact that it is partially fermented by bacteria in the colon to acetate and butyrate, lowering fecal pH. Polydextrose also increases fecal bulk, reduces fecal transit time and softens stools. Measured by the standard AOAC Official Method of Analysis for TDF, polydextrose would have no TDF value. Given the arguments for a new dietary fiber definition, this is understandable. A new method has been developed and validated and accepted as an official AOAC method.

An in with inulin
Another interesting member of the RO group are the fructooligosaccharides (FOS), found naturally in 36,000 plants worldwide. (The primary source of natural FOS in the United States is wheat, although FOS also is found in garlic, onions, leeks and its major natural source — chicory.)

Inulin is a beta-2,1 fructan with a DP of 2 to 60, with over half of the dry weight at a DP less than 20. According to Pam Galvin, product manager, Imperial-Sensus, Sunnyland, TX, inulin also stimulates bifidobacteria and suppresses detrimental bacteria in the gastrointestinal tract, reduces liver toxins and provides immune-stimulation properties. “For physiological effects to be realized, a minimum of 5 grams daily consumption is required for modification of microflora,” she notes. Inulin has a glycemic index of zero and contributes only 1.6 kcal/gram.

Scientific studies have established that inulin and oligofructose improve the bioavailability of minerals such as calcium, magnesium and iron; significant increases are noted with about 15 grams of inulin per day. But, according to Stephanie Dettore, applications scientist at Orafti Active Food Ingredients, Malvern, PA, “New clinical studies have shown that a proprietary new enriched form of inulin can boost calcium absorption by 20% with just 8 grams per day.” The BoneMax study, conducted at the USDA/ARS Children’s Nutrition Research Center at Baylor College of Medicine in Houston, TX, involved 29 girls aged 11 to 14 over a six-week period. “This higher efficiency can be explained by the specific distribution of chain lengths in the new inulin, which slows fermentation so that calcium is absorbed over the entire length of the colon,” she says.

Inulin, in addition to providing prebiotic and mineral absorption benefits, also can contribute positively to food texture. “Inulin is readily soluble in water (60 grams/liter at 10ºC, 330 grams/liter at 90ºC) and is slightly hygroscopic,” states Galvin. “Synergistic effects have been noted with other gum-based stabilizers and gelling agents. Inulin helps to bind water, add viscosity and improve mouthfeel in many food systems, and has been commercialized in breads, dressings, pasta and seafood. Most successful commercial applications with inulin are in the 2% to 4% range, depending on inulin’s function.”

More soluble solutions
Another unique RO is a spray-dried maltodextrin created by the pyrolysis and controlled enzymatic hydrolysis of cornstarch. This is marketed as Fibersol®-2 by Matsutani America, Inc., Decatur, IL. Similar to the case involving polydextrose, this product demonstrates no TDF by the official AOAC method, but a new AOAC official method for “resistant maltodextrins” was recently approved in April 2001.

The solubility of Fibersol-2 is high at 70% w/w at 20ºC, and its viscosity in solution is very low, which makes it a very useful source of soluble fiber in beverage applications. The company claims 90% soluble dietary fiber on a dry solids basis. In terms of carbohydrate distribution, DP7+ is greater than 80%, and DP1 comes in at 1.5%, so its molecular weight is in the general range of an FOS. Clinical studies on this fiber ingredient have shown that it improves intestinal microflora, ferments to short-chain fatty acids, increases fecal bulk, lowers serum cholesterol levels and has a relatively low glycemic response.

Have you tried fenugreek fiber? As you may have noted, fenugreek is a spice noted for its strong odor and flavor — it is used heavily in curry. However, fenugreek seeds contain approximately 40% of a soluble fiber, mucilage. Fenugreek fiber is obtained from the seeds of Trigonellafoenum gracum, cultivated in India, Egypt, the Middle East and North Africa. The seeds have been used in remedies for diabetes, inflammation, kidney problems and gastrointestinal distress. A number of clinical studies also have indicated that fenugreek can contribute to lower levels of glucose in the blood of diabetics.

According to Joseline Mather, RN, Schouten USA Inc., Minneapolis, “The unique galactomannan ratio of galactose and mannose (1:1) in fenugreek fiber seems to be responsible for its blood glucose reduction properties, as well as unique emulsifying properties in foods such as dairy products and salad dressings.” These unique properties led to the development of a new breed of fenugreek developed at the University of Saskatchewan, Saskatoon. This new type, developed by traditional breeding (non-GMO), is lower in oil and higher in soluble fiber than traditional plants.

Laurent Leduc, vice president of sales and marketing at Schouten, notes “Through a unique patented extraction process, we were able to decrease the taste and odor associated with fenugreek, which resulted in FenuLife® odorless fenugreek extract, which was first introduced in May 2001.” This extract contains a minimum of 85% TDF, of which 65% minimum is soluble fiber. “The first targeted market was dietary supplements, primarily encapsulated tablets, drinks and functional foods, such as bars and chewable candies,” he says. “Our studies indicate that 1 to 2 grams taken five to 10 minutes before meals and before bedtime can help to lower blood glucose levels and provide satiation.” Since about 6% of the U.S. population currently has diabetes, with numbers continuing to rise, the potential of this type of product is promising.

Other fiber sources may play a role in the future. Flaxseed has a relatively high level of fiber, about 28% TDF, that may provide nutritional value as a dietary fiber. About two-thirds of this fiber is insoluble nonstarch polysaccharides, such as cellulose and lignin. These may contribute to digestive health. The water-soluble portion, approximately one-third of the total fiber, consists mainly of mucilage gum, which may help maintain blood glucose levels and lower cholesterol. However, the physiological effects may not be due to the fiber alone; the flaxseed protein, oil and lignans also may assist in providing these health benefits.

Progress on insoluble fiber blends
Improvements for insoluble fibers also have been noteworthy. According to Jit Ang, vice president, research and development, International Fiber Corporation (IFC), North Tonawanda, NY, “We have developed a new insoluble fiber based on bamboo to add to our traditional cellulose- and cottonseed-based fibers. This new vegetable fiber is high in TDF, is creamy white, has no odor or flavor, and can provide a smoother mouthfeel than traditional insoluble fiber ingredients. Applications would be beverages, sauces, cream soups, frozen novelties, etc.”

Blended fiber ingredients based on soluble and insoluble ingredients can be custom tailored. “At the IFT in June 2001, we demonstrated the application of a blend of vegetable fiber and inulin in several beverage products,” notes Ang. “At the IBIE exhibition in September 2001, we demonstrated different blends in a bakery item. This new concept of blending insoluble fibers with soluble components has spread rapidly throughout the industry.”

On a similar note, at the USDA/ ARS Eastern Regional Research Center, Wyndmoor, PA, Charles Onwulata has applied for a patent to increase cereal fiber content in snack foods through extrusion of the fibers with milk proteins to control water-holding capacity of the fiber. Onwulata claims the ability to produce a nutritional bar with 15 grams of fiber per 50 gram bar. Although palatability is not necessarily a high priority in some of the nutritional bars now on the market (although this is steadily improving), this process could also lead to some interesting new fiber products.

Fiber’s future
This covers only some of the new products and new thought relative to the current discussions on fiber definition by NAS and AACC. But look for more fiber advances and opportunities in the future. “Despite the clearly understood health benefits of adequate fiber consumption, American consumers still eat on average far too little fiber,” says Stowell. “Traditionally, scientists and legislators have found it difficult to agree on a definition for fiber and this has hindered innovation, particularly where new ingredients are concerned. We at Danisco welcome the recent initiatives by both the AACC and the NAS. These groups have identified the need for a definition of fiber based on physiological effects. Put simply, this approach will enable consumers to take advantage of new food innovations and improve the nutritional profile of their diet.”

Once the definition dilemma is resolved — and this should be sometime within the next year — we can hope that consumer education on the benefits of fiber will become easier, opening new markets for fiber. Industry innovation relies heavily on what can be claimed on the label, and the health claims currently allowed under the Nutrition Labeling and Education Act (NLEA) include:
• Diets low in fat and rich in fiber-containing grain products, fruits and vegetables may reduce the risk of some types of cancer.
• Diets low in saturated fat and cholesterol and rich in fruits, vegetables and grain products that contain fiber, particularly soluble fiber, may reduce the risk of coronary heart disease.
• Diets low in fat and rich in fruits and vegetables, which are low-fat foods and may contain fiber or vitamin A (as beta-carotene) and vitamin C, may reduce the risk of some cancers.
• Soluble fiber from foods such as oat bran (or oatmeal, rolled oats or whole oat flour), as part of a diet low in saturated fat and cholesterol, may reduce the risk of heart disease. The words “diet low in saturated fat and cholesterol” are required in this health claim. In order to make this claim, a food must provide at least 0.75 grams of soluble fiber per serving. This claim was later amended to include psyllium seed husk (PSH) fiber. In order to make the claim, foods must contain at least 1.70 grams of soluble fiber from PSH per serving. In amending the claim, FDA also stated that “since soluble dietary fibers are a family of very heterogeneous substances that vary greatly in their effect on risk of coronary heart disease, a case-by-case approach is necessary to evaluate petitions for health claims on fiber.”

This is a very encouraging statement, and shows the level of commitment from FDA in reaching agreement on dietary-fiber definition. “It is vital that legislation keeps pace with innovation,” Stowell says. “Only by doing so will consumers be able to take advantage of new developments and thus improve the nutritional profile of their diet.”

Based on the level of progress from AACC and NAS, we are close to reaching a new level in the use of fiber in consumer foods. Next step for food and ingredient manufacturers, in concert with the health community: renew consumer education.

Ronald C. Deis, Ph.D., is the director, product and process development, at SPI Polyols, Inc., New Castle, DE. Deis has 20 years of experience in the food industry, both in food ingredients (starches, polyols, high potency sweeteners, bulking agents) and in consumer product companies (cookies, crackers, soups, sauces). He has been a shortcourse speaker (polyols, fat replacers) and a freelance writer on a number of food science related subjects in food journals and has contributed chapters on sweeteners and fat replacers for several books.

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