Determination of digestible energy values and fermentabilities of dietary fibre supplements: a European interlaboratory study in vivo.

The performance of methods to determine energy conversion factors for dietary fibre (DF) supplements and fermentability (D) values of their non-starch polysaccharides (NSP) was investigated. Heats of combustion, digestible energy (DE) and D values were determined on five DF supplements in five European laboratories on five separate occasions. In each instance the DF supplements were fed to juvenile male Wistar rats at two doses, 50 and 100 g/kg basal diet, for 3 weeks with food and faeces collected in the 3rd week. Among-laboratory variations in heats of combustion (delta Hc) were < 2%. DE values (kJ/g dry weight) at the upper and lower doses respectively were: 10.4 and 9.9 for a high-methoxyl apple pectin, 9.5 and 9.4 for a sugar-beet DF supplement, 12.2 and 12.7 for soyabean DF supplement, 3.8 and 4.0 for maize bran, and 0.3 and 0.3 for Solka-floc cellulose. Variations among laboratories, among occasions and among animals were < 1, < 2 and < 2.5 kJ/g respectively. The among-occasion: among-laboratory variance ratio for DE was 0.5, suggesting the method performed equally well in all laboratories. There was no evidence of learning of fatigue or fatigue in the performance of the method. D values were also independent of dose and at the high and lower doses were: pectin 0.92 and 0.95, sugar-beet NSP 0.68 and 0.68, soyabean NSP 0.86 and 0.88, maize bran 0.17 and 0.18, cellulose 0.07 and 0.06. Among-laboratory variance tended to increase with decreasing fermentability and ranged from 0.03 to 0.18. The DE and D data were not significantly different from a previously proposed relationship DE = 0.7 x delta Hc x D, where delta Hc is the heat of combustion of the supplement. We conclude that while the among-laboratory variation in the D of difficult-to-ferment NSP is too large for the reliable prediction of energy value the method for the direction determination of DE is both reproducible and repeatable, that DE is independent of dosage of DF supplement up to 100 g/kg diet, and that it is safe to discriminate between energy values with a precision of 3 kJ/g. The conversion of both DE and D to net metabolizable energy for the purpose of food labelling, tables and databases is described.

Digestion and absorption of sorbitol, maltitol and isomalt from the small bowel. A study in ileostomy subjects.

OBJECTIVE: To quantify small bowel digestion and absorption of sorbitol, isomalt and maltitol in ileostomy patients and estimate the metabolizable energy. SUBJECTS: Study A: Nine ileostomy patients, under a constant controlled diet, ate during three consecutive days 2 milk chocolate bars per day, containing 2 x 15 g of polyol, each day with another polyol in random order. The first bar was taken 30 min after breakfast, and the second bar, 7 h after breakfast. Effluents were recovered during the whole study. Study B: 5, 10 or 20 g of sorbitol or isomalt were consumed each day in a drink during two 3-day periods by two ileostomy subjects. The recovery in the ileal effluent was measured over 24 h. RESULTS: Study A: Carbohydrate recovery in ileostomy effluent was 26.8 +/- 2.8% (mean+SEM) for sorbitol, 24.8 + 5.7% for maltitol (2/3 as sorbitol) and 40.0 +/- 0.7% for isomalt (1/3 being sorbitol and mannitol). Ileal excretion, compared with a day without polyol, was compared in 4 subjects. The total volume excreted, as well as dry matter increased after polyol consumption. When taking this extra loss into account, the metabolizable energy value of the polyols for 2 x 15 g intake were: sorbitol, 12 kJ/g (2.8 kcal/g); maltitol, 13 kJ/g (3.1 kcal/g); isomalt, 9 kJ/g (2.1 kcal/g). Study B: The level of digestion and absorption of both sugar alcohols was dose dependent. CONCLUSIONS: These results indicate that sorbitol, maltitol and isomalt are rather extensively absorbed, but the digestibility of the other nutrients is also reduced, due to the osmotic load caused by the polyols in the small intestine. There are evidences of a dose dependency of the energy value of the polyols.

Fibre-mediated physiological effects of raw and processed carrots in humans.

Fibre-mediated physiological effects of raw and processed carrots were investigated in twenty-four young women under strict dietary control in two randomized crossover studies. For 3 weeks between 405 and 688 g of either raw frozen, blanched or canned carrots (first study), or raw or raw frozen carrots (second study) were consumed in addition to a low-fibre basal diet. Carrots provided 15 g dietary fibre (DF)/d. Total DF intake was 16.0 to 19.0 g (control periods) and 31 to 34 g (experimental periods). Faecal bulking effects of raw and processed carrots were similar (between 2.4 and 3.7 g additional stool/g carrot fibre in the diet). Faecal excretion of dry matter, fibre, and protein also increased significantly during carrot consumption. Fermentability of carrot fibre constituents was high (91-94%) and independent of processing, in spite of differences in the distribution of soluble and insoluble fibre and in the texture of raw and processed carrots. There was no effect of either type of carrot on serum total and high-density-lipoprotein-cholesterol or on faecal bile acid excretion.

Determination of soluble dietary fiber in foods and food products: collaborative study.

A collaborative study was conducted to determine the soluble dietary fiber (SDF) content of foods and food products by using a combination of enzymatic and gravimetric procedures. The method was basically the same as that employed for determining total dietary fiber (TDF), 985.29, and the method for insoluble dietary fiber (IDF), 991.42. Ten laboratories were each sent 13 test samples (6 blind duplicates and 1 standard [green beans] containing 29-33% TDF, 19-23% IDF, and 8-13% SDF) and were instructed to assay for IDF, SDF, and TDF independently. Included in the package were the 3 enzymes, namely alpha-amylase, amyloglucosidase, and protease, and the filter aid Celite, which was thought to be the major cause of high reproducibility relative standard deviation (RSDR) values for SDS obtained in a previous collaborative study. The foods to be analyzed were apricots, carrots, chickpeas, onions, raisins, and the sugar beet fiber Fibrex. IDF, TDF, and SDF were calculated as the weight of residue minus the weight of protein and ash on a dry weight basis. RSDR values of the IDF results averaged 8.02%, with only 1 food having an RSDR > 10%. The RSDR values for the TDF results averaged 4.97%, and all foods had an RSDR < 7%. Although the RSDR values for SDF averaged 14.17%, 4 of the 6 foods had an RSDR < 10%, and 1 of the 2 remaining foods that had a high RSDR had an SDF content of only 1.2%.(ABSTRACT TRUNCATED AT 250 WORDS)

The physiological and nutritional importance of dietary fibre.

Fibrous material is an integral part of the daily diet, and it exerts direct physiological effects throughout the gastrointestinal tract, in addition to affecting metabolic activities more indirectly. The interplay of these effects is responsible for the presumed desirable influence of fibre on weight regulation, carbohydrate and lipid metabolism, and on colon function. Numerous mechanisms of action have been identified which are related to the type and the physicochemical nature of the fibre. This review concentrates mainly on the serum cholesterol-lowering effect of dietary fibre, its colonic fermentation, and finally on some possible adverse effects that one should be aware of when consuming high amounts of dietary fibre.

Nutrients excreted in ileostomy effluents after consumption of mixed diets with beans or potatoes. I. Minerals, protein, fat and energy.

The small intestinal excretion of protein, fat, energy, magnesium, calcium, iron and zinc from two isocaloric diets including either instant bean flakes (174 g/d) or potato flakes (102 g/d) was studied in seven ileostomy subjects. Out of the variable part of the diet all starch and dietary fibre, and about half of the energy was provided from bean flakes or potato flakes, respectively. The small variation in ileostomy excretion between two consecutive days, after one adaptation day, suggests that ileostomy studies can be performed with reasonable precision in 2 days. During the 2-day potato period average daily excretions of gross energy and protein were 236 kcal (988 kJ; 11 per cent of intake) and 13 g (12 per cent), respectively. The excretions were significantly (P less than 0.001) higher during the bean period, 378 kcal (1582 kJ; 16 per cent) and 17 g (15 per cent). Fat intake and excretion were not different. After making allowance for dietary fibre, the apparent nutrient energy digestibilities were over 90 per cent, with only 43 kcal (180 kJ; 2 per cent) difference between the two periods. Apparent absorption of magnesium was lower during the bean period, 7 per cent compared to 25 per cent (P less than 0.02). The study has thus shown that only slightly less apparent small intestinal absorption occurs from a diet with bean flakes compared to potato flakes, so the nutritional consequences of beans on other nutrients seem to be small.

Nutrients excreted in ileostomy effluents after consumption of mixed diets with beans or potatoes. II. Starch, dietary fibre and sugars.

The extent of carbohydrate digestion and absorption from two diets including either instant bean flakes (174 g/d) or potato flakes (102 g/d) was measured in seven ileostomy subjects during a 2-day period. Test foods contributed 40 per cent of the total dietary starch intake (160 g/d), the remainder coming from rice and white bread. Overall, 4 per cent and 0.7 per cent of the dietary starch consumed remained unabsorbed during the bean and potato periods, respectively. Between 9.0 and 10.9 per cent of dietary bean starch and less than 1.7 per cent of potato starch were not absorbed. Dietary fibre and resistant starch were completely recovered in ileostomy effluents. In separate meal tests with 40 g starch, beans gave lower blood glucose (P less than 0.05) and serum insulin (P less than 0.01) responses than potatoes. Dietary starch malabsorption from leguminous foods is less than previously estimated and does not explain the attenuated glycaemic and insulinaemic responses.

Fermentation of vegetable fiber in the intestinal tract of rats and effects on fecal bulking and bile acid excretion.

The fermentative breakdown and fecal bulking capacity of dietary fiber from various vegetables (carrots, rutabagas, peas, green beans and Brussels sprouts) were evaluated in balance experiments in rats. The excretion of bile acids, protein and fat was also studied. The addition of blanched vegetables providing 10 g of fiber/100 g of diet caused a two-(rutabagas) to threefold (carrots) increase in fecal dry weight compared to that with a basal fiber-free diet. With green beans and Brussels sprouts, only about 25% of the fecal dry weight could be accounted for as fiber, whereas with the other investigated vegetables, 40-47% was fiber. Of the remaining part, 11% on average was fat, and 18% was crude protein. Fiber in carrots and peas was the least degraded, with approximately 47% of the polysaccharide intake being excreted in feces. By contrast, the breakdown of the fiber in green beans and Brussels sprouts was more extensive, with a mean of 23% of the polysaccharides being recovered. Among individual fiber constituents, glucose, mannose and uronic acids were least fermented, with considerable differences between vegetables. Total excretion of bile acids was reduced only when Brussels sprouts were added, whereas the concentration of fecal bile acids was lowered with all vegetables except rutabagas. However, no uniform change in fecal bile acid pattern could be detected.

Gastric emptying and glycemic response after ingestion of mashed bean or potato flakes in composite meals.

Two meals of mashed-bean or potato flakes and meat were served in random order to six healthy male subjects to determine effects on gastric emptying and glycemic reactions. The meals had comparable physical appearance and contained similar amounts of digestible carbohydrate, fat, and protein. No difference in gastric emptying, recorded by gamma camera after mixing 51Cr with the meals, was found between the meals. The bean-flakes meal gave significantly lower blood glucose (p less than 0.01) and serum insulin (p less than 0.05) concentrations than did the potato-flakes meal. The overall blood glucose response, calculated as incremental area under the curves for 2 h, also differed between the meals (p less than 0.05) whereas the overall insulin response did not differ significantly. The low glycemic response after bean flakes could not be explained by the gastric emptying rate, which provides additional evidence for the slow digestion of bean starch in the small intestine.

Hydrogen excretion after ingestion of five different sugar alcohols and lactulose.

The breath hydrogen excretion was measured for 5 h after the initial rise on seven subjects who consumed randomly, and after 5 d of adaptation, equimolar amounts of sorbitol (10 g), mannitol (10 g), maltitol (19 g), Palatinit (19 g anhydrous), lactitol (19 g anhydrous), lactulose (19 g) in aqueous solution. The mean mouth-to-caecum transit time was 1.5 h, which was not significantly different from one carbohydrate to another, but varied significantly from one subject to another (0.7-2.4 h). Suprabasal increment of breath hydrogen after lactitol was significantly higher than that from the other polyols (P less than 0.001) over 5 h. Lactitol and lactulose, which are known to be totally undigested in the small intestine, gave the highest mean incremental area under the breath hydrogen curve, 327 p.p.m. H2 over 5 h and 224 p.p.m. H2 over 5 h, respectively. The values for the other test compounds ranged from 145 to 209 p.p.m. H2 over 5 h, which suggest that there had been only partial absorption in the small intestine.

Determination of insoluble, soluble, and total dietary fiber in foods and food products: interlaboratory study.

A collaborative study was conducted to determine the insoluble dietary fiber (IDF), soluble dietary fiber (SDF), and total dietary fiber (TDF) content of food and food products by using a combination of enzymatic and gravimetric procedures. The method was basically the same as that developed for TDF only, which was adopted official final action by AOAC, except for changing the concentration of buffer and base and substituting hydrochloric acid for phosphoric acid. These changes were made to improve the robustness of the method. Duplicate blind samples of soy isolate, white wheat flour, rye bread, potatoes, rice, corn bran, oats, Fabulous Fiber, wheat bran, and a high fiber cereal were analyzed by 13 collaborators. Dietary fiber values (IDF, SDF, and TDF) were calculated as the weight of residue minus the weight of protein and ash. The coefficients of variation (CVs) of both the independent TDF determination and the sum of IDF and SDF were better than 15 and 18%, respectively, with the exception of rice and soy isolate. These 2 foods, however, contained only about 1% TDF. The CVs of the IDF were equally good, except for Fabulous Fiber, for which filtration problems occurred. The CVs for the SDF were somewhat high, but these products had very low SDF content. There was excellent agreement between the TDF determined independently and the TDF determined by summing the IDF and SDF. The method for separate determination of IDF and SDF requires further study. The modifications (changes in concentration of buffer and base and the use of hydrochloric acid instead of phosphoric acid) to the official final action method for TDF have been adopted.

Determination of total dietary fiber in foods and food products: collaborative study.

A collaborative study was conducted to determine the total dietary fiber (TDF) content of food and food products, using a combination of enzymatic and gravimetric procedures. The method was basically the same as published earlier (J. Assoc. Off. Anal. Chem. (1984) 67, 1044-1052), with changes in the concentration of alcohol and buffers, time of incubation, sample preparation, and some explanatory notes, all with the intent of decreasing the coefficient of variation (CV) of the method. Duplicate blind samples of soy isolate, white wheat flour, rye bread, potatoes, rice, wheat bran, oats, corn bran, and whole wheat flour were analyzed by 9 collaborators. TDF was calculated as the weight of the residue minus the weight of protein and ash. CV values of the data from all laboratories for 7 of the samples ranged from 1.56 to 9.80%. The rice and soy isolate samples had CV values of 53.71% and 66.25%, respectively; however, each sample contained only about 1% TDF. The enzymatic-gravimetric method for determining TDF has been adopted official first action.

A quantitative determination by capillary gas-liquid chromatography of neutral and amino sugars (as O-methyloxime acetates), and a study on hydrolytic conditions for glycoproteins and polysaccharides in order to increase sugar recoveries.

Complete gas-liquid chromatographic separation of O-methyloxime acetates (syn and anti isomers) prepared from eight neutral sugars, three hexosamines, and muramic acid has been obtained, using a fused-silica Carbowax 20M capillary column. A single hydrolytic step for carbohydrate-containing biological material (less than or equal to 2.5 X 10(-3) M sugar solution in 4 N trifluoroacetic acid at 125 degrees C for 1 h) has been developed, and results have been compared with those obtained with standard hydrolytic conditions in order to ensure complete release of amino sugars from glycoproteins, together with minimum losses of neutral sugars. The combination of this acid hydrolysis with the above improved derivatization procedure for the gas-liquid chromatographic analysis has led to a simple, rapid, and sensitive analytical method, which has been successfully tested on three glycoproteins (fetuin, mucin, and peroxidase) and two plant cell-wall polysaccharide fractions (soluble fibers from carrots and soybeans).

Metabolic effects of dietary fiber from dehulled soybeans in humans.

The normal diet of six healthy volunteers was supplemented by 21 g of dietary fiber from two different soybean seed fiber preparations, either a nonpurified and never-dried soya pulp A (39% dietary fiber) or a purified soya fiber B (79%), for 3 wk each. Mean daily fecal wet weight was increased by 19 and 38% in the fiber periods A and B as compared to a 2-wk control period (p less than 0.05). Stool frequency and transit time remained unchanged. Fecal fiber increased by 52% only during period B. Fecal calcium, magnesium, and iron were increased (p less than 0.05), mainly after higher intakes during both fiber periods. Excretion of neutral steroids remained unchanged, but their concentration was lowered (p less than 0.05). A 21% increase of fecal bile acids by fiber A was specifically due to deoxycholic acid (+32%, p less than 0.01). Oral glucose tolerance was slightly improved after period B. Neither fiber changed serum triglycerides, but fiber B increased low-density lipoprotein-cholesterol by 19% (p less than 0.01) and low-density lipoprotein-phospholipids by 16% (p less than 0.05). The ratio high-density/low-density lipoprotein-cholesterol, however, did not change significantly. Thus, dietary fibers from soybean do not seem to contribute to the hypocholesterolemic effect of soya. The results of this study also demonstrate that two apparently similar dietary fibers, coming from a single source, can exert distinctly different metabolic effects.