According to the Centers for Disease Control and Prevention (CDC), obesity is rapidly becoming the number-one preventable cause of death in the United States (Mokdad et al., 2004). The alarming rise in obesity began in the 1970s and has been growing even more rapidly in recent years. From 1991 through 1998, the prevalence of adult obesity increased by 57% (Mokdad et al., 1999).
Recent studies point to increased consumption of calories from food as a primary cause. According to a CDC report (Wright et al., 2004), between 1971 and 2000, American men increased energy consumption on average from 2,450 kcal/day to 2,618, while American women increased consumption from 1,542 kcal/day to 1,877. For every 3,500 kcal of energy not burned, we add one pound of body weight. Unfortunately, Americans do not appear to have increased energy expenditure at a rate comparable to energy consumption.
In recognition of this alarming problem, the Food and Drug Administration created the Obesity Working Group to make recommendations for reversing the unhealthy trend. The Working Group issued its final report on March 12, 2004, focusing on the scientific fact that weight control is primarily a function of caloric balance. In announcing the recommendations of the Working Group, FDA Deputy Commissioner Lester Crawford said, "We’re going back to basics, designing a comprehensive effort to attack obesity through an aggressive, science-based, consumer-friendly program with the simple message that calories count." Adding encouraging support to FDA’s education program, "Calories Count," is the recent analysis by Hill et al. (2003), which concludes that a program of reducing energy intake by as little as 100 kcal/day "could prevent weight gain in most of the population."
Fiber, Weight Control, and Health
One relatively easy solution for Americans to tip the balance in caloric intake is to add more fiber to their diets. Consumption of more fruits and vegetables, which are high in moisture and dietary fiber, has long been advocated as a sensible way to manage weight (Rolls et al., 2004).
The specific role of dietary fiber in regulating body weight has been analyzed by a team of researchers at the Jean Mayer USDA Human Nutrition Research on Aging at Tufts University (Howarth et al., 2001). These researchers analyzed numerous published studies, on the effects of dietary fiber on hunger, satiety, energy intake, and body composition in healthy individuals. They found that a majority of the studies indicate that an increase in dietary fiber increases post-meal satiety and decreases subsequent hunger.
Summing all the published studies, the researchers found that healthy individuals who consumed an additional 14 g/day of fiber for more than 2 days as part of their normal diet experienced a 10% decrease in energy intake and body weight loss of 1.9 kg over 3.8 months. The loss in weight over this time period is equivalent to reducing caloric intake by a little more than 100 kcal/day, in support of Hill’s observations.
Surprisingly, the Tufts study found that body weight loss in obese individuals was even greater, amounting to 2.4 kg over the same time period. The observed changes in energy intake and body weight occurred whether the dietary fiber was consumed in the form of high-fiber foods or fiber supplements. Similarly, the same effect was found for both soluble and insoluble forms of fiber. More-recent studies continue to support the Tufts findings (Liu et al., 2003). Consuming more fiber in the diet can help reduce caloric intake and weight over a reasonable period of time.
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Americans do not consume nearly enough fiber in their diets. The mean dietary fiber intake is currently about 15 g/day (Miller-Jones, 2004). This level is in sharp contrast with the intake of 25–38 g/day recommended by the American Heart Association and the National Academy of Sciences (IOM, 2002). The Tufts researchers concluded in their paper cited above that "efforts to increase dietary fiber in individuals consuming less than 25 g/day may help to decrease the currently high national prevalence of obesity."
Unfortunately, the growing interest in low-carbohydrate, high-protein diets appears to be reducing the consumption of carbohydrates. Not all carbohydrates are alike when it comes to gaining weight. Unlike simple sugars and most forms of starch, dietary fiber is not digested and absorbed by the body. Only soluble fiber contributes any significant amount of energy through fermentation in the large intestine. On average, about 40% of all fiber is fermented, with most of this being soluble fiber (Jeraci et al., 1993). As a result, dietary fiber lowers the energy density of food, while increasing satiety and reducing hunger. In addition, fiber increases the viscosity of the gastrointestinal fluid, impeding mass flow and absorption of molecules in the small intestine, slowing the digestion of fat and starch, and the transport of glucose into the blood stream (Dohnalek, 2004). The net result is that increased consumption of dietary fiber as part of a healthy diet, either in foods naturally high in fiber or from foods supplemented with fiber, can lead to the gradual loss of weight by reducing caloric intake (Buchholz and Schoeller, 2004).
Increased consumption of fiber is also associated with a reduced risk of developing certain types of cancer, including colon cancer (McIntosh, 2004). This is presumably due to the formation of short-chain fatty acids in the large intestine from fermentation by beneficial bacteria. Short-chain fatty acids, especially butyrate, are the primary source of energy for the colonic cells, enhancing cell growth and differentiation (Schneeman, 2001). A recent study showed that fiber (as powdered cellulose supplement) exhibited a preventive effect against the formation of colon cancer in rats, which was greater than the promotive effect of fat (fed as lard), when fed as part of the same diet (Nakaji et al., 2004). Finally, a very recent analysis of the National Health and Nutrition Examination Survey (NHANES) by researchers at CDC showed a significant inverse correlation between dietary fiber intake and blood serum levels of C-reactive protein, a marker of inflammation and possible predictor of future heart disease (Ajani et al., 2004). Clearly, consumption of more fiber would be beneficial for the health of the American public.
FDA is currently in the process of developing a formal definition for dietary fiber. In terms of functionality, it is useful to define fiber as being either soluble or insoluble in aqueous systems. Insoluble fiber comes from the remnants of plant cell walls, while soluble fiber is found primarily in the space between the cell walls called the middle lamella.
Insoluble fiber is composed of cellulose, hemicelluloses, and lignin. Cellulose is a pure polymer of glucose molecules linked exclusively through nondigestible β-1,4 bonds. Hemicelluloses are branched polysaccharides made of many different sugars. Soluble fibers are composed of complex polysaccharides such as β-glucans, pectins, gums, and some hemicelluloses. Cellulose, and most hemicelluloses, and associated lignin, are structured, pseudo-crystalline polymers held together by strong molecular forces of hydrogen bonding that are not disrupted by water and are therefore insoluble in gastrointestinal fluid and poorly fermented by gut microflora.
Soluble fiber is hydrophilic, non-crystalline, and easily wetted by the aqueous gastrointestinal fluid, forming viscous colloidal dispersions (sols) or gels when hydrated. Soluble fiber is extensively fermented by gut microflora.
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Both soluble and insoluble forms of fiber are available as purified ingredients for incorporation into foods. To purify insoluble fiber for use as a food ingredient, much of the lignin must be removed during the isolation process by extraction with alkali. Lignin is a complex cross-linked polymer of aromatic alcohols, which provides rigidity to the plant cell walls. If insufficient lignin is removed during the extraction process, the fiber will be more rigid, fragile, and easily discolored by oxidation. Most insoluble fiber is bleached with hydrogen peroxide to produce a whiter fiber for use in food.
In addition, removal of the lignin produces an insoluble fiber, which is highly porous and capable of absorbing a significant amount of water. Generally, the more lignin that is removed, the greater the porosity and water-holding capacity of the fiber.
Many plant raw materials, such as trees, soy and oat hulls, and wheat stalks can serve as sources of insoluble fiber. Wood contains the highest level of cellulose (about 50%), as well as high levels of lignin, and can be subjected to the most rigorous extraction conditions. The well-known Kraft pulping process (sulfate process) produces a highly porous, pure insoluble cellulose known as α-cellulose. Wood is also far less likely to be contaminated with pesticide residues and has no GMO issues.
Powdered cellulose is produced by grinding pure cellulose to various particle sizes. Powdered cellulose is the purest form of insoluble fiber, containing the highest level of cellulose and the least amount of hemicellulose, lignin, and ash, as shown in Table 1.
On a dry-weight basis, powdered cellulose contains more than 99% insoluble dietary fiber, as measured by the American Association of Cereal Chemists’ Approved Method 32-05 (AACC, 2000). Powdered cellulose, therefore, contributes no calories to the food, making it perhaps the most effective fiber for reducing the energy content of food (Vetter, 1994). A typical nutritional profile of powdered cellulose is shown in Table 2. Like the cellulose in plant cell walls, which occurs as microfibrils, powdered cellulose retains the long fibrous structure. This structure provides a very large ratio of surface area to weight while also providing a large internal pore volume. Air-permeability studies using a Blaine’s apparatus provided values of up to 8,000 cm2/g of internal and external surface-to-weight ratio (Ang, 2001). As a hydrophilic (water-loving) polymer of glucose, powdered cellulose has very high water-holding capacity (WHC), compared to other cellulosic fibers.
The range of WHC for each fiber varies with the particle size. The larger the particle size (or length of fiber), the more water that can be held as a result of the greater internal pore volume. Therefore, the WHC of powdered cellulose can be controlled by particle size.
When formulating foods with powdered cellulose, more water can be added than with the other cellulosic fibers. More water in the formulation not only reduces costs, but more important, means that the total number of grams of carbohydrate in the product will be less on a weight, serving size, and percent basis than without the addition of powdered cellulose. Therefore, the addition of powdered cellulose and water not only increases the total dietary fiber content of the food, but also reduces the total number of calories and grams of carbohydrate on a weight basis. This is a healthy formula for helping Americans lose weight.
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Applications of Powdered Cellulose
As a pure polymer of glucose, powdered cellulose functions as an effective inert substitute for a significant portion of the rapidly metabolized sugars and starch in a wide variety of flour-based products. Its porous, fibrous structure provides high WHC to retain moisture, while also providing a heat-stable framework for maintaining the physical form and texture of baked goods, such as breads, buns, bagels, biscuits, cookies, muffins, and pizza crust. In addition, powdered cellulose contributes no off-flavors or color and is calorie-free. It is available in a wide range of particle sizes to retain the desired mouthfeel.
The carbohydrate, fiber, and caloric content of selected flour-based products formulated with powdered cellulose compared to standard formulations is shown in Table 3. Nutrition data for the standard formulations were obtained from tables compiled by ESHA Research in Salem, Ore. (Smolin and Grosvenor, 2000). In addition to the powdered cellulose, various protein sources, such as vital wheat gluten and soy and wheat protein isolates, were substituted for a portion of the wheat flour. Thus, all formulations prepared with powdered cellulose contain higher levels of protein than the standard formulations. In all cases, the addition of powdered cellulose significantly increased fiber content, while reducing total carbohydrate and caloric content.
• Breads. Powdered cellulose plus additional water can be used to replace a portion of the flour in a typical bread formulation made by the sponge-and-dough process. The resulting bread contains about 46% less total carbohydrate, 20% fewer calories, and more than three times the level of dietary fiber than a standard formulation. Protein content is increased to 6.5 g/serving compared to 2 g for the standard formulation. Hamburger buns can also be prepared by a similar sponge-and-dough process to yield a bun with 31% less total carbohydrate, 25% fewer calories, and nearly four times more dietary fiber than standard buns.
Other bread-like products such as some types of bagels, focaccias, and pizza crust are considered old-European style artisan breads. Powdered cellulose also works well in these products to increase fiber content and reduce the levels of total carbohydrates and calories. Pizza crust formulated with 4.9% powdered cellulose contains 50% less total carbohydrate, 40% fewer calories, and almost three times more fiber than standard pizza crust. Protein content is increased almost three-fold. Bagels prepared with powdered cellulose show a similar reduction in total carbohydrate and caloric content.
• Flour Tortillas. Flour tortillas are rapidly becoming a popular replacement for bread when used as sandwich wraps. The healthy image of flour tortillas can be further enhanced by the substitution of powdered cellulose for a portion of the flour. The resulting tortillas contain almost 50% less carbohydrate and calories, more than five times as much fiber, and double the protein content per serving than a standard formulation. In addition, powdered cellulose increases moisture retention, improves pliability, extends shelf life, and replaces some of the functionality of fat.
• Dry Pasta. Concern regarding the high carbohydrate content of pasta has resulted in a decrease in consumption of this very popular food. Again, substitution of 5.2% powdered cellulose for a portion of the semolina flour results in a reduction of 50% of the carbohydrate content, 28% fewer calories, and 1.7 times more fiber than a standard formulation. The inclusion of additional wheat protein provides a healthy formulation delivering 8 g of protein/28-g (dry) serving, compared to just 3 g of protein in the standard formulation.
The above formulations are designed to provide a desirable balance between the quality of the product in terms of mouthfeel, texture, and taste and the carbohydrate, fiber, and caloric content. Other formulations, which increase or decrease these attributes, are possible.
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Some Final Thoughts
The old saying "a calorie is a calorie" refers to the fact that for every calorie of energy consumed, a calorie must be burned to maintain energy balance and avoid weight gain or loss. Thermodynamics dictates that a calorie is a calorie regardless of the composition of the diet (Buchholz and Schoeller, 2004). Unfortunately, it is not possible to maintain perfect energy balance on a daily, or even weekly basis. Therefore, we must find ways of consuming less energy to offset the days we consume a surplus of energy.
Consuming more fiber in the diet is one way of achieving this net result. However, high-fiber diets based on fruits, vegetables, and whole-grain foods can be fairly expensive, leading some nutrition researchers to conclude that obesity in the U.S. is inversely related to the cost of food (Drewnowski and Specter, 2004). Lower-cost foods tend to be higher in calories because of the high content of fats and sugars and low content of fiber.
The analysis by Howarth et al. (2001) confirms that "fiber is fiber." Fiber, whether it is from foods supplemented with high-fiber ingredients or foods naturally high in fiber, reduces the energy density of food and increases the feeling of satiety. The use of fiber supplements in processed foods is a convenient and cost-effective way to introduce more fiber into the diet. Pure powdered cellulose contains the highest level of dietary fiber of any food-approved ingredient.
Energy-dilute foods, such as fruits and vegetables, also tend to be high in water (Drewnowski and Specter, 2004). With its very high water-holding capacity, powdered cellulose is one of the most cost-effective ingredients for introducing more water into foods, thus further reducing the energy density of the food. The substitution of powdered cellulose for flour, together with additional water and protein, is a cost-effective approach to create new, high-quality, healthy formulations of flour-based products with increased fiber and protein contents and reduced caloric and carbohydrate contents. Foods formulated with powdered cellulose can supplement naturally high-fiber fruits, vegetables, and whole grain foods in a healthy diet.
Author Ang is Executive Vice President, International Fiber Corp., 50 Bridge St., North Tonawanda, NY 14120. Author Crosby, a Professional Member of IFT, is Consultant in Food and Nutrition Chemistry, 18 Sunset Rd., Weston, MA 02493, and Visiting Lecturer at Harvard School of Public Health and Framingham State College. Send reprint requests to author Ang.
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