Dietary Fiber Values Research Articles

Adequate intake values for dietary fibre based on faecal bulking indexes of 66 foods.

To determine an adequate daily intake value for dietary fibre (AIdf) based on faecal bulking indexes (FBIs) for 66 foods of known total dietary fibre (TDF) content. FBIs of 66 foods were measured and expressed as wheat bran equivalents (WBEfb) per 100 g of food. A daily WBEfb requirement for humans was calculated from faecal bulk generated per gram of wheat bran TDF in humans, using a critical faecal mass of 200 g/day for protection against large bowel disease. TDF content was regressed against WBEfb content for all 66 foods assayed, and an AIdf value obtained by substituting the calculated human WBEfb requirement into the regression equation. FBI was measured using a validated rat assay, with eight large (400+/-50 g) rats per group, preadapted to dietary fibre, and fed adequate restricted diets containing test foods at inclusion rates consistent with human intakes. The critical faecal mass was based on epidemiological studies, and the faecal bulk generated per gram of wheat bran TDF was the mean of 27 published values. WBEfb requirements for humans were calculated to be 90 g/day, corresponding to a faecal output of 200 g/day. The regression equation relating WBEfb measured in the FBI assay to TDF in all 66 foods was TDF=0.491WBEfb + 3.19, R2=0.81 Substituting the human WBEfb requirement of 90 g into the regression equation gave an AIdf value of 40.9 g TDF/day. The AIdf value of 40.9 g TDF/day based on faecal bulking supports the AIdf of 38 g TDF/day recently set by the Institute of Medicine (USA), for young men, based on protection against heart disease. The AIdf value is obtained from the relation between the effects of foods and their content of mixed function, plant cell wall dietary fibres within the food matrices, and should not be used to guide intakes of extrinsic functional polysaccharides.

Raisin dietary fiber composition and in vitro bile acid binding.

Raisins are dried grapes that are popular shelf-stable snacks. Three commercially important types of raisins were studied: sun-dried (natural), artificially dried (dipped), and sulfur dioxide-treated (golden) raisins. Dietary fiber composition was analyzed by AACC method 32-25. Polysaccharides were hydrolyzed, and the resulting sugars were analyzed by colorimetric and gas chomatographic methods. Fructans were measured with a colorimetric kit assay. Total dietary fiber values agreed with published values, with pectins and neutral polysaccharides of mannose and glucose residues predominating. Dipped raisins had over 8% fructans. No fructans were found in fresh grapes. Raisin types varied in their ability to bind bile acids in vitro. Coarsely chopped raisins bound more bile than did finely chopped or whole raisins.

Individual Sugars, Soluble, and Insoluble Dietary Fiber Contents of 70 High Consumption Foods

As part of the continuous efforts of the Nutrient Data Laboratory, Agricultural Research Service (ARS), USDA in updating and expanding the carbohydrate data in its database, foods were selected based on dietary fiber content and frequency of consumption. They were analyzed by a commercial testing laboratory under a USDA contract. Individual sugars, soluble and insoluble dietary fiber values of 70 foods in six food groups were reported. Foods included 14 baked products, 10 cereal grains and pastas, 19 fruits, seven legumes, 10 cooked vegetables, and 10 raw vegetables. Except for cereal grains/pasta and legumes, most other foods contained fructose and glucose; sucrose was found in almost all except baked products, which were the most predominant source of maltose. Fruits contained the most total sugar and cereal, grains/pasta the least. Legumes contained the highest amount of total dietary fiber. All these commonly consumed foods, with the exception of cooked white rice, contained both soluble and insoluble dietary fiber. The percent of soluble and insoluble fiber varied across food groups, even within each group. Comparison of data from the commercial laboratory with those of the same food analyzed in the Food Composition Laboratory using different methods indicated there was good agreement between high-performance liquid chromatographic and gas chromatographic methods for the determination of individual sugars. Total dietary fiber as calculated from the sum of soluble and insoluble fiber according to AOAC Method 991.43 and total dietary fiber from direct analysis using a single enzyme-gravimetric method showed high variability ( r 2<0.8) for three of the six food groups, but good agreement for others.

Importance of Enzyme Purity and Activity in the Measurement of Total Dietary Fiber and Dietary Fiber Components

A study was made of the effect of the activity and purity of enzymes in the assay of total dietary fiber (AOAC Method 985.29) and specific dietary fiber components: resistant starch, fructan, and beta-glucan. In the measurement of total dietary fiber content of resistant starch samples, the concentration of alpha-amylase is critical; however, variations in the level of amyloglucosidase have little effect. Contamination of amyloglucosidase preparations with cellulase can result in significant underestimation of dietary fiber values for samples containing beta-glucan. Pure beta-glucan and cellulase purified from Aspergillus niger amyloglucosidase preparations were used to determine acceptable critical levels of contamination. Sucrose, which interferes with the measurement of inulin and fructooligosaccharides in plant materials and food products, must be removed by hydrolysis of the sucrose to glucose and fructose with a specific enzyme (sucrase) followed by borohydride reduction of the free sugars. Unlike invertase, sucrase has no action on low degree of polymerization (DP) fructooligosaccharides, such as kestose or kestotetraose. Fructan is hydrolyzed to fructose and glucose by the combined action of highly purified exo- and endo-inulinases, and these sugars are measured by the p-hydroxybenzoic acid hydrazide reducing sugar method. Specific measurement of beta-glucan in cereal flour and food extracts requires the use of highly purified endo-1,3:1,4 beta-glucanase and A. niger beta-glucosidase. Beta-glucosidase from almonds does not completely hydrolyze mixed linkage beta-glucooligosaccharides from barley or oat beta-glucan. Contamination of these enzymes with starch, maltosaccharide, or sucrose-hydrolyzing enzymes results in production of free glucose from a source other than beta-glucan, and thus an overestimation of beta-glucan content. The glucose oxidase and peroxidase used in the glucose determination reagent must be essentially devoid of catalase and alpha- and beta-glucosidase.

Dietary fiber content of commonly fresh and cooked vegetables consumed in India.

Legumes, leafy vegetables, roots and tubers, gourds and other vegetables were analyzed for total (TDF), soluble (SDF) and insoluble (IDF) dietary fiber contents, both before and after cooking either by a conventional open-pan method or by pressure cooker. Data revealed a significant increase in SDF fraction with a concomitant decrease in the IDF fraction upon cooking by both the methods employed. Although the decrease in IDF matched the increase in SDF values in some cases, it was found to be more in vegetables categorized as 'other'. The dietary fiber values have also been reported on a fresh weight basis which may serve as a guideline for calculating dietary intake of each component by the consumer.

Nutritional Profile of Some Edible Plants from Mexico

Five samples of Chaya (Cnidoscolus chayamansaL.) and other edible plants widely consumed in Mexico for their nutritional and medicinal properties were analyzed for proximate components, selected minerals and vitamins, and essential amino acids. Protein in these plants (mostly leaves) ranged between 20.0 and 36.2% (dry weight basis) and showed a good amino acid profile. Dietary fiber values ranged between 23.1 and 41.8% (dry weight basis), but this fiber was essentially all insoluble fiber. These plant materials contained significant amounts of calcium, potassium, magnesium, riboflavin, and niacin; other minerals and vitamins were also present in appreciable amounts. Because of this nutritional profile, these materials make a significant dietary contribution. They also have potential for use in functional foods.

Effect of Seeds on Bile-Enzymatic-Gravimetric Analysis of Total Dietary Fiber

Dietary fiber sometimes is defined chemically as nonstarch polysaccharides plus lignin or as other specific chemical entities. Analysis of dietary fiber according to a chemical definition typically involves gas chromatography, which allows separation and quantitation of chemical constituents that are added to arrive at a dietary fiber value. Other definitions of fiber are broader, defining it to be whatever is not digested in the alimentary tract. Analytically, this definition translates into the gravimetric sum of the material remaining after a series of enzymatic and chemical treatments that simulate in vivo digestion. Various methods reflect the gravimetric definition, which might include as dietary fiber some protein, resistant starch, and even lipids that are not digested by particular assay conditions. We used a recently proposed bile-enzymatic-gravimetric assay for total dietary fiber on commonly consumed seeds (hulled and unhulled sesame, caraway, and poppy) and visually found these seeds to be undigested. We then determined the impact of the undigested seeds on measured dietary fiber content by spiking homogenized daily menus with 5% by weight of these seeds and calculating recoveries with 2 assumptions: seeds are 100% fiber because they are not digested, and the fiber content of seeds is as determined by assay. Calculated recoveries were very different depending on which assumption was made (71-90% or 99-109%, respectively), and the difference was closely related to the seed's protein content.

Hard wheat bran and hard wheat bran fiber energy values measured in rats after 6 and 16 weeks.

The difficulties in determining the energy values of dietary fiber (DF) sources in human studies include the following: 1) The control over food intake, 2) the long-term maintenance of dietary changes (Stevens et al., 1987), 3) the cost and the large number of dietary combinations to be assessed. Models for predicting the energy value of DFs in humans have improved over the last decade (Livesey, 1995) but energy-balance experiments in animals are important due to the limited number of human studies (Livesey, 1990a). The rat model is particularly useful for long-term experiments and it has been recommended for predicting the digestibility of dietary components and energy (Bach Knudsen et al., 1994; Wisker et al.,1996).

Effect of Lipid Extraction Methods on Total Dietary Fiber and Nonstarch Polysaccharide Contents of Selected Nuts and Seeds

Three extraction methods were used to remove lipid materials from 8 edible nuts and seeds before analysis for their total dietary fiber (TDF) and nonstarch polysaccharide (NSP) contents. Portions of ground materials were extracted by: n-hexane, followed by 80% methanol, n-hexane-acetic acid (95 + 5, v/v), and supercritical carbon dioxide. Defatted samples were gelatinized in water and incubated with amyloglucosidase; 95% ethanol was added to the hydrolyzates, and the residues were collected on tared glass crucibles. TDF was calculated according to a simplified enzymatic-gravimetric method developed in our laboratory, and NSP was determined as described by Englyst and coworkers. Dietary fiber values obtained with any of the extraction methods range from 3.47 g/100 g for cashews to 28.56 g/100 g for sunflower seeds. Nonstarch polysaccharide values range from 2.43 g/100 g for pecans to 5.56 g/100 g for peanuts. With the exception of sunflower seeds, samples extracted with supercritical carbon dioxide had lower TDF contents but similar amounts of NSP compared with samples extracted by the other 2 methods.

The classification and measurement of dietary carbohydrates

Major advances in our understanding of the digestive physiology of dietary carbohydrates and their potential benefit to health require new and more informative techniques to replace the traditional ‘by difference’ measurement. The human diet contains a range of chemically distinct carbohydrates and research, as well as labelling for dietary carbohydrates including dietary fibre, should be based on the classification and measurement of chemically identified components. Such values do not become obsolete and can be used in different combinations for different purposes. We present a new scheme for carbohydrate classification, including a new class of short-chain carbohydrates (SC). The classification and measurement of nutritionally important types of starch includes its division into rapidly digestible starch (RDS), slowly digestible starch (SDS) and resistant starch (RS). In addition, a new category of rapidly available glucose (RAG) is described, which is the amount of glucose from free sugar and starch that is rapidly available for absorption. Values for dietary fibre based on the measurement of plant cell-wall NSP aid the consumer in choosing the type of high-fibre diet recommended in the dietary guidelines and are, therefore, appropriate for food labelling. The AOAC Prosky procedure, in contrast, is not specific for plant cell-wall material but includes substances that are formed by food processing and by treatment of analytical samples. Such values are not suitable for food labelling because they do not aid the consumer in choosing the recommended diet.

Determination of Sugars, Starches, and Total Dietary Fiber in Selected High-Consumption Foods

A general scheme has been developed to determine sugars, starches, and total dietary fiber (TDF) in half-gram freeze-dried subsamples of various foods (or wet samples containing about 0.5 g dry matter). Duplicate subsamples are extracted for free sugars with 80% methanol, dried, derivatized to their trimethylsilylated oximes or ethers, and quantitated by gas-liquid chromatography (GLC). Residues after 80% methanol extraction are incubated with a solution containing amyloglucosidase in acetate buffer. Hydrolyzates are centrifuged, and duplicate aliquots are removed for glucose determination by GLC. Starch content is calculated as glucose (g/100 g) x 0.9. Remaining hydrolyzates are diluted with 4 volumes of 95% ethanol, left at room temperature for 1 h, and then filtered through glass crucibles matted with Celite filter aid. The weight of dry residues are corrected for residual crude protein and ash, and the resulting values are taken to be the TDF content of a sample. A variety of high-consumption foods selected by the Nutrient Data Laboratory of the Agricultural Research Service were analyzed for carbohydrate fractions by this method. Values for total sugar and dietary fiber were compared with those obtained by a commercial laboratory using different methods.

Prediction of Total Dietary Fiber in Cereal Products Using Near-Infrared Reflectance Spectroscopy

The Nutritional Labeling and Education Act of 1990 has increased the need for more rapid, efficient, and nonpolluting techniques of analyzing the nutrients in foods, particularly dietary fiber. The use of near-infrared spectroscopy (NIRS) for the prediction of total dietary fiber content of cereal products was investigated in this study. Cereal and grain products, including breakfast cereals, flours, brans, crackers, and samples containing commercial oat and wheat fibers, were selected for analysis. Products (n = 91) were dry milled, and total dietary fiber was measured by the AOAC (991.43) enzymatic-gravimetric method. Total dietary fiber values ranged from <1 to 52% of dry weight. Milled cereal products (n = 91) were scanned from 1100 to 2498 nm with a NIRSystems 6500 monochromator. Using ISI software for scanning and data analysis, a dietary fiber calibration was obtained with partial least squares as the regression method. The standard error of cross validation and multiple coefficient of determination were 1.58% and 0.99, respectively. For equation validation, an independent group of cereal products (n = 31) was dry milled, and total dietary fiber was determined. The samples were scanned, and total dietary fiber was predicted by NIRS. Samples were predicted with a standard error of performance of 1.51%, coefficient of determination of 0.99, bias of −0.38, and slope of 1.06. This study shows that NIRS can be used to rapidly and accurately predict total dietary fiber content in a wide range of cereal products. Keywords: Dietary fiber; near-infrared spectroscopy; nutrition labeling

Effects of Nutrition Education on Menu Planning at Sorority Houses

Menu planners in small foodservice facilities are often challenged to design menus that are nutritious and appealing to consumers. The purpose of this study was to determine to what extent sorority women consider nutrition when making food choices and to assess the effects of nutrition education on housemothers who plan menus for sorority houses. One hundred and fifty women at 5 selected sorority houses on one campus were surveyed. Results revealed that 32% of these women almost always consider nutrition when making food choices, and 55% sometimes consider nutrition. However, 100% of the women sometimes or almost always considered taste and preference when making food choices, and over 80% were almost always concerned about weight loss and weight gain. Over 1/2 almost always preferred whole wheat bread, and approximately 3/4 almost always or sometimes consumed 3 servings of vegetables and 2 servings of fruits daily. Housemothers at the 5 sorority houses submitted three days of menus to the researcher. Analysis using Minnesota NDS, vers 2.5, showed that these menus contained less than 100% of the RDA for vitamin D, calcium, iron and zinc for this age group. The mean fat content was 85g. and dietary fiber content was 20g. A nutrition education workshop was held for the housemothers with information presented on the USDA Dietary Guidelines, Food Pyramid and strategies for reducing fat and increasing fiber in menus. Following the workshop, each housemother modified menus to improve them nutritionally. Probably due to the small number of sorority houses participating, analysis of the modified menus did not show significant changes in values of fat, dietary fiber, minerals and most vitamins. However, the value of vitamin B6 increased significantly (p 0.01), and mean daily fat content in menus was reduced to 64.5g. and fiber content increased to 24g. Calcium and vitamin D amounts remained deficient, probably related to the decrease in fat content of the modified menus. Results indicate that individuals attending a workshop on how to use nutritional guides can be influenced to improve the nutrient content of menus. Since approximately 16,000 women live in sorority houses on U.S. college campuses, education of menu planners at these facilities is important in improving the diets of college women.

Starch and Dietary Fiber Components Are Excreted and Degraded to Variable Extents in Ileostomy Subjects Consuming Mixed Diets with Wheat- or Oat-Bran Bread

The study was conducted to determine if the excretion of starch and dietary fiber components varies in ileostomy subjects consuming diets high or low in dietary fiber. Excretion of starch, enzyme-resistant starch and dietary fiber components was studied in nine human subjects with ileostomies, who consumed (in a crossover design) a wheat bread-based diet (daily intake 274 g starch, 2.4 g enzyme-resistant starch and 14.4 g total dietary fiber) and a high fiber diet based on oatbran bread (daily intake 243 g starch, 2.7 g enzyme-resistant starch and 40.2 g total dietary fiber). Food and excreta were collected on d 3 and 17. No significant differences in excretion of starch, enzyme-resistant starch or dietary fiber components were found on these 2 d in each dietary period. When subjects consumed the wheat bread-based diet they excreted (mean ±SD) 3.3 ± 1.7 g starch and 2.4 ± 0.4 g enzyme-resistant starch daily, whereas when consuming the oat bran-based diet they excreted 4.5 ± 3.1 g starch and 2.5 ± 0.4 g enzyme-resistant starch. During both dietary periods subjects excreted significantly greater amounts of certain dietary fiber polysaccharide residues (fucose, galactose and uronic acid) than they ingested. This indicates a contribution of endogenous and/or microbial material to the dietary fiber value in ileostomy effluents. However, significantly less excretion of some dietary fiber polysaccharide residues, especially glucose residues, during the oat-bran bread-based dietary period was also noted. This was presumably caused by a degradation of mixedlinked.

The influence of extruded vs. untreated barley in the feed, with and without dietary enzyme supplement on broiler performance

The experiment was conducted to study the effect of extruded vs. unprocessed barley in the diet (400 g kg −1) on the response of broiler chickens to Trichoderma viride enzyme supplement (cellulase, 10 500 U g −1; endo-β-(1:3) (1:4)-glucanase; 24 000 U g −1 and xylanase, 32 000 U g −1). The four experimental diets were as follows: B, unprocessed barley; BE, unprocessed barley + enzyme (200 mg kg −1); ExB, extruded barley; ExBE, extruded barley + enzyme (200 mg kg −1). The diets were fed as pellets. Extruded compared with unextruded barley gave higher soluble fibre (28 vs. 36 g kg −1) and lower insoluble (190 vs. 163 g kg −1) and total (219 vs. 200 g kg −1) dietary fibre values. Extrusion increased extract viscosity (1.3 vs. 3.7 cP) and water binding capacity (1.6 vs. 2.2 ml g −1 dry matter) of the barley. During the first week, birds fed extruded barley in the diet increased water consumption ( P ≤ 0.05). A significant depression in feed efficiency (days 7–21), feed AME, and in fat and protein utilisation was observed when extruded barley was included in the diet. Extrusion reduced the AME content of barley by 0.82 MJ kg −1 DM. Inclusion of extruded barley in the diet potentiated the weight gain (2.8 vs. 7.6%; P = 0.31) and feed efficiency (+ 0.8 vs. −6%; P = 0.07) response to dietary enzyme. Greater enzyme effects with the diet containing extruded barley were also found for feed AME (1.6 vs. 2.9%; P = 0.39), fat utilisation (0.4 vs. 5.4%; P ≤ 0.05), nitrogen utilisation (−0.5 vs. 5.6%; P = 0.12), as well as β-glucan degradability (10.4 vs. 15.6%; P = 0.41). In general, the enzyme had more impact on chick performance than barley form.

Comparison of Three Methods and Two Cooking Times in the Determination of Total Dietary Fiber Content of Dried Legumes

Freeze-dried samples of a variety of dried legumes cooked according to package instructions were analyzed for their total dietary fiber using a recently published method (I) which utilizes porcine pancreatic enzymes. The values from the latest study compared those obtained previously using simplified single enzyme method (II) and an AOAC/MES-Tris buffer method 991.43 (III). Total dietary fiber content varied form 17% (g/100 g dry weight) for chickpeas to 30% for kidney beans as determined by methods (I) and (II), and 30 to 58% with the same legumes using method (III). Comparisons were also made using (II) and (III) on the effect of cooking time on the total dietary fiber values for 10 legumes. Greater variations were found in fiber content between cooking times with method (III). Variations between brands of the same legumes were also more pronounced with the AOAC method. This may be accounted for by the day to day variability of the method when used on samples containing high starch.

Time Trend of Dietary Fiber Intake in Japan, 1917-1991

The per capita daily intake of dietary fiber (DF) in Japan between 1917 and 1991 was assessed using statistical reports regarding nutrition, food consumption, production, and trade balance. The reported contents of DF for each food category were used ; these values were based on the modified Southgate method and modified Prosky AOAC method. Average per capita daily consumptions of total DF calculated by the modified Southgate method were 30.3 g in 1917-1924 and 15. 6 g in 1991. Those calculated by modified Prosky AOAC method were 28.6 g in 1917-1924 and 14. 5 g in 1991. Both calculation methods yielded values indicating that the DF intake had been almost constant in the last 20 years. Differences in the calculated values of DF obtained by the two methods are attributed mainly to the difference in the measured values for rice. J Epidemiol, 1995; 5 : 205-210.

Excretion and Degradation of Dietary Fiber Constituents in Ileostomy Subjects Consuming a Low Fiber Diet with and without Brewer's Spent Grain

AbstractExcretion of total dietary fiber and dietary fiber components was studied in 10 human subjects with ileostomies, consuming in a crossover design a low fiber diet (15 g total dietary fiber/d) or this diet supplemented with 62 g/d of brewer's spent grain. Food and excreta were collected and analyzed on d 2, 3 and 7 of each dietary period. No significant differences in excretion of total dietary fiber or dietary fiber components were found on the three days. Excreta from subjects consuming the low fiber diet contained significantly more total dietary fiber than was ingested (20%, P < 0.01), indicating the importance of endogenous and microbial material, contributing to the total dietary fiber value, in ileostomy effluents. Analysis of specific dietary fiber components showed that this increased excretion was mainly due to fucose, mannose, galactose and uronic acid residues. When the high-fiber diet was consumed, there was a significantly greater excretion of the same non-starch polysaccharide residues as for consumption of the low fiber diet, but with a simultaneous decrease in excretion of arabinose, xylose and glucose residues (12%, P < 0.01), which were the major fiber components in the diet.

Total Dietary Fiber Content of Selected Nuts by Two Enzymatic–Gravimetric Methods

Eight nuts (almond, cashew, macadamia, peanut, pecan, pistachio, sunflower, and walnut) were analyzed for total dietary fiber content using a simplified enzymatic–gravimetric method and a AOAC/MES–TRIS buffer method. Mean total dietary fiber values for three brands of each type of nut ranged from 3.6% for cashew to 14.9% for macadamia, with the other nuts having values between 6.2 and 10.5%. Variability between brands for a given nut is greater than that between the mean of two methods. Chemical analysis of selected dietary fiber residues for nonstarch polysaccharides (the sum of neutral sugars and uronic acids) indicated that for certain nuts, for example macadamia and almonds, high total dietary fiber values may be due to components other than nonstarch polysaccharides and lignin.

Dietary Fiber Content of Cereal and Grain Products Determined by Enzymatic–Chemical and Enzymatic–Gravimetric Methods

The two objectives of this research were to compare total dietary fiber values obtained by the AOAC enzymatic–gravimetric method and the Uppsala enzymatic–chemical method for 50 grain and cereal products and to compare the fiber content and composition of foods that are likely to be grouped during nutrient intake studies. Mean fiber contents of 44 refined grain products determined by the two methods were significantly different ( P < 0.01), 2.5 ± 1.2 g/100 g (fresh wt) by the AOAC method and 2.0 ± 0.7 g/100 g by the Uppsala method. Mean fiber contents of 6 higher fiber foods also were different ( P < 0.01), 9.1 ± 1.6 and 7.9 ± 1.2 g/100 g, respectively. Data from the two methods of analysis were strongly correlated, r 2 = 0.93 ( P < 0.001). The soluble fiber content of the refined products was an average of 25% of total fiber, of the higher fiber products, 20%. Ingredients influenced the fiber content and composition of the samples; some such as fat and sugar diluted the fiber concentration and others such as fruit, nuts, coconut, and chocolate increased it. We conclude that complete descriptions should be obtained if food intake records are to reflect fiber intake; grouping some foods prior to calculating fiber intake is likely to lead to errors and fiber intakes calculated from AOAC fiber data will be higher than those determined by the Uppsala fiber method. Because a more specific set of analyses would be likely to provide more accurate results, we recommend that data obtained using an enzymatic–chemical method be used to calculate fiber intake in nutritional studies.