Effect of Heat Treatment on Dietary Fiber: Interlaboratory Study

The effects of thermal treatments on the dietary fiber composition of cereal and potato samples were studied at 8 laboratories using different analytical methods. Thermal treatments included extrusion cooking for cereals, and boiling and frying for potatoes. No changes in the amounts of dietary fiber or starch were observed in the extruded samples. Heat-treated potato samples contained significantly more water-insoluble dietary fiber (cellulose) and less starch than did raw potato. However, this may be due, at least in part, to the sample preparation procedure rather than the heat treatment alone. The study indicates that gravimetric and sequential hydrolysis methods give similar results, but the variation in most cases is still wide. Further standardization of methods is evidently needed, especially if legislative measures for setting limits on the fiber content of foods are to be introduced. Standardization of starch analysis should also be of primary importance in future work on carbohydrate methodology. This can be concluded from the variation in results concerning this extremely important food constituent. It should be noted that the sample matrix in the present study was simpler than that of complex meals or diets.

Effect of dietary fibre on blood glucose, plasma immunoreactive insulin, C-peptide and GIP responses in non insulin dependent (type 2) diabetics and controls

A high fibre and a low fibre breakfast meal were given to eight non insulin dependent diabetics ( NIDD ), and eight controls. Blood glucose response was monitored continuously for three hours and characterized using a straight line model. After the high fibre meal the rates of increase and decrease in blood glucose concentration were slower both in diabetics and controls than after the low fibre meal. The delay time, however, i.e. the time from meal intake to the start of glucose increase, hypothetically corresponding to gastric emptying time, was the same after both test meals. The postprandial glucose increment calculated as the area under the 0-120 min curve was lower after the high fibre meal in the NIDD , but not in the controls. The two-hour C-peptide and gastric inhibitory polypeptide values were lower for the diabetics after the high fibre breakfast. The results indicate a prolonged carbohydrate digestion and/or absorption after high fibre breakfast.

Dietary fibre in type II diabetes

Recent studies have indicated that diets rich in digestible carbohydrates and dietary fibre might be beneficial in the regulation of type II non insulin dependent diabetes (NIDD). Addition of the gel forming type of dietary fibre such as pectin and guar gum to meals or glucose solutions reduces post-prandial glucose and insulin response. Addition of cereal fibres in the form of bran seems to have long term beneficial effect improving glucose tolerance. Little is known, however, concerning effects of dietary fibre naturally occurring in food on postprandial glucose and hormone response. In the present study we prepared two breakfast meals which were similar regarding digestible carbohydrates but differed in their dietary fibre content. One of the meals, including whole grain bread and whole apples, contained 8.4 g of dietary fibre, and the other one, containing white bread and apple juice, 3.1 g. When given to eight NIDD, the fibre rich breakfast gave significantly lower blood glucose increment during the three hours following ingestion. The results indicate that foods rich in dietary fibre might be useful in the regulation of type II diabetes.

Improved glycemic control and lipid profile and normalized fibrinolytic activity on a low-glycemic index diet in type 2 diabetic patients

OBJECTIVE

To evaluate the effects of varying the glycemic index (GI) of carbohydrate-rich foods on metabolic control in type 2 diabetic patients.

RESEARCH DESIGN AND METHODS

In a randomized crossover study, 20 patients, 5 women and 15 men, were given preweighed diets with different GIs during two consecutive 24-day periods. Both diets were composed in accordance with dietary recommendations for people with diabetes. The macronutrient composition and type and amount of dietary fiber were identical. Differences in GI were achieved mainly by altering the structure of the starchy foods.

RESULTS

Peripheral insulin sensitivity increased significantly and fasting plasma glucose decreased during both treatment periods. There was a significant difference in the changes of serum fructosamine concentrations between the diets (P < 0.05). The incremental area under the curve for both blood glucose and plasma insulin was approximately 30% lower after the low- than after the high-GI diet. LDL cholesterol was significantly lowered on both diets, with a significantly more pronounced reduction on the low-GI diet. Plasminogen activator inhibitor-1 activity was normalized on the low-GI diet, (-54%, P < 0.001), but remained unchanged on the high-GI diet.

CONCLUSIONS

A diet characterized by low-GI starchy foods lowers the glucose and insulin responses throughout the day and improves the lipid profile and capacity for fibrinolysis, suggesting a therapeutic potential in diabetes.

Retrograded high-amylose corn starch reduces cholic acid excretion from the small bowel in ileostomy subjects

OBJECTIVE

To study the short-term effect of resistant starch (RS) from retrograded high-amylose corn starch (HACS) on the excretion of bile acids and nutrients from the small bowel in humans.

DESIGN

Seven healthy ileostomists were given a controlled, constant diet during three days. On days 2 and 3, 100 g/d of one of two test-products--drum-dried ordinary corn starch and autoclaved retrograded HACS, providing 5 and 39 g RS/d, respectively--was given, in random order. Ileostomy effluents were collected for 24 h per day and analysed for wet weight, dry weight, energy, bile acids and nutrients.

SETTINGS

In-patient study at the metabolic ward, Department of Clinical Nutrition, Sahlgrenska University Hospital, Göteborg.

RESULTS

Consumption of retrograded HACS caused (1) a 42% lower mean excretion of cholic acid (P = 0.024); (2) a 42% lower mean wet weight concentration of bile acids (P < 0.001); (3) a 70% increased excretion of dry weight (P = 0.001); and (4) a 41% increased excretion of energy (P= 0.036) compared with consumption of drum-dried ordinary corn starch.

CONCLUSION

The reduced ileal excretion and concentration of cholic acid would be protective regarding colon cancer risk in addition to the increased fermentation substrate provided by RS and other energy-yielding components.

Functional food science and substrate metabolism

The present review addresses the role of food constituents in the aetiology of metabolic conditions and chronic diseases, mostly related to energy metabolism and substrate regulation, such as obesity and non-insulin-dependent diabetes mellitus. Second, attention is paid to malnutrition, a major cause of mortality and morbidity in developing countries, which may be a cause of concern in Europe because of the increasing number of elderly people in the population. Finally, the role of diet during exercise, a condition of enormous substrate demands, is evaluated. Based on a critical evaluation of the existing knowledge in the literature, implications for future research in relation to functional foods are discussed.

Resistant starch--an update on its physiological effects

Resistant starch (RS) has emerged as one of the main substrates for colonic fermentation, together with other undigestible polysaccharides and oligosaccharides. There are indications that RS may be a good source of butyrate, and that the rate and site of fermentation can be varied and optimized. This makes RS potentially important for colonic health, and production of food products containing RS challenging. The present RS content in most Western diets is probably low, but can be increased by foods high in RS. The physiological effects of RS are reviewed, as well as the formation of RS in foods and its analysis.

Influnce of oat saponins on intestinal permeability in vitro and in vivo in the rat

The aim of the present study was to investigate whether oat saponins (avenacosides A and B) have any effect on the permeability of the rat intestine to actively and passively transported markers in vitro and in vivo. Intestinal segments were mounted in modified Ussing chambers, and the passage of the different marker compounds from the mucosal to the serosal side was measured for 120 min. Avenacosides (1 mg/ml) gave a significantly higher passage of the macromolecule ovalbumin and there was a tendency to increased passage of [14C]D-mannitol and [51Cr]EDTA. On the other hand, the saponins did not affect the active transport of [3H]methyl glucose. When rats were given saponins (40 mg/kg body weight) together with markers by gastric intubation, the passage of [51Cr]EDTA into blood and urine was somewhat reduced. For the macromolecule bovine serum albumin, no evident effect on the passage was observed in the presence of saponins. Thus, in contrast to the in vitro results, the in vivo marker passage seemed to be unaffected or even reduced in the presence of avenacosides. The study shows that saponins can affect the permeability of the rat intestine. However, this effect needs further investigation in vivo, especially regarding proteins.

Satiety effects of spinach in mixed meals: comparison with other vegetables

The effects of vegetables in mixed meals on satiety were evaluated by varying the dose (portions 150 and 250 g containing 4.3 and 7.2 g of dietary fibre, respectively) and structure (cut and minced) of microwaved spinach. A control meal without spinach and the test meals with spinach were balanced regarding energy (2000 kJ) and digestible carbohydrates (59 g, 51 E%) and with protein and fat as far as possible similar. The meals were served in the morning, after an overnight fast, to ten healthy male volunteers. Satiety was registered and blood glucose as well as plasma insulin and C-peptide were analysed at regular intervals until 3.5 h postprandially. The largest spinach portions augmented satiety and reduced the postprandial glucose response. The total satiety scores seemed to be correlated positively to both the dietary fibre and the water content in the vegetable. Differences in structure had no influence on satiety scores.

Effect of oat saponins and different types of dietary fibre on the digestion of carbohydrates

The effects of oat saponins (a mixture of avenacosides A and B) and dietary fibre (cellulose and guar gum) on the disaccharidase activities in the proximal small intestine of the rat were investigated. The influence of avenacosides A and B on the activity of disaccharidases and alpha-amylase (EC 3.2.1.1) was also studied in vitro. In vivo, oat diets with three avenacoside contents (negligible, normal and twice normal) were used. No significant differences in sucrase (EC 3.2.1.48), maltase (EC 3.2.1.20), trehalase (EC 3.2.1.28) and lactase (EC 3.2.1.21) activities were found between the oat groups after 19 d feeding. The rats that were given cellulose tended to have higher disaccharidase activities compared with the other groups. The avenacosides inhibited the lactase activity significantly in vitro while no or small effects on the other disaccharidases were found. In contrast, the in vitro hydrolysis of starch by alpha-amylase was increased in the presence of saponins, probably due to their detergent effect. Thus, the in vitro studies showed that the avenacosides could influence the enzyme activities. In vivo, these effects are probably minor due to the low avenacoside concentrations found in oats.

The influence of food structure on postprandial metabolism in patients with non-insulin-dependent diabetes mellitus

Two natural-food mixed meals composed in accordance with the present dietary recommendations were given to 10 diabetic patients on two occasions. The meals were planned to achieve large differences in glycemic index (GI) by altering the food structure but maintaining an identical nutrient composition. In the first study, two meals were compared that contained either pasta or bread made from durum wheat flour. In the second experiment a meal with parboiled rice, red kidney beans, and bread made from whole-wheat grains was compared with a meal of sticky rice, ground red kidney beans, and bread made from ground wheat. All of the other ingredients in these meals were identical. The area under the curve for blood glucose (BG) and plasma insulin (PI) was significantly lower after the meal with pasta (BG: -35%, P < 0.05; PI: -39%, P < 0.05) and the meal with parboiled rice (BG: -42%, P < 0.001; PI: -39%, P < 0.01), respectively, compared with the corresponding high-GI meals. The results shows the importance of preserved structure in common foods and support the applicability of the GI concept to mixed meals.

Classification and methodology of food carbohydrates as related to nutritional effects

Dietary guidelines encourage a considerable increase in carbohydrate intake compared with the present situation in Western countries. Recent developments regarding nutritional effects of various digestible and undigestible carbohydrates call for more detailed recommendations. The "carbohydrates by difference" concept emerged 150 y ago because of the lack of specific analytical techniques and still prevails. The concept of available compared with unavailable carbohydrate was introduced in 1929 to obtain a better measure of glucogenic carbohydrates in diabetes. Dietary fiber was first defined as the "skeletal remnants of plant cell walls," but the definition was later expanded to include all polysaccharides and lignin that are not digested in the small intestine. The gravimetric method of the Association of Official Analytical Chemists for total dietary fiber is based on this undigestibility concept. However, precipitation of soluble fiber components with alcohol, which is used in all current methods, creates an arbitrary delimitation between oligo- and polysaccharides. The complex carbohydrates concept is challenged by recent developments regarding nutritional effects of various food carbohydrates.

Influence of processing and cooking of carrots in mixed meals on satiety, glucose and hormonal response

The influence of processing and cooking on the metabolic response to carrots in mixed meals was explored in two consecutive harvest years. The contribution of dietary fibre (4.4 g 1989 and 6.6 g 1990) from carrots was chosen to be different in order to compare effects with varying doses. The meals, composed of carrots, creamed potatoes, meat balls, lingonberry jam, white bread and light beer, were served in the morning after an overnight fast to 10 healthy male volunteers. Carrots were investigated raw, processed (blanched and frozen) and variously cooked (thawed, boiled and microwaved). The amount of dietary fibre from the vegetable, and the content of energy, digestible carbohydrates, fat and protein were similar in the meals compared. Significantly lower glucose, insulin and C-peptide responses and higher satiety scores were elicited with raw carrots than with microwaved ones, harvest year 1989. The next year, with a higher dietary fibre intake from carrots, there were significant effects of processing only on the glucose response. Plasma beta-carotene levels tended to be higher postprandially with raw carrots than with microwaved ones. Hence, ordinary processing and cooking of vegetables can affect the metabolic response to a mixed meal. However, the influence seems to be varying and of minor importance in ordinary meals. Increasing vegetable portions entailing a higher soluble fibre content and a higher viscosity could further reduce the influence of processing.

Effect of oat saponins on plasma and liver lipids in gerbils (Meriones unguiculatus) and rats

The effects of oat saponins (a mixture of avenacosides A and B) on plasma and liver lipids in gerbils (Meriones unguiculatus) and rats were investigated. Cholesterol-containing diets high in total and saturated fat and with different avenacoside contents (zero (ethanol-extracted oats), normal (oats) and twice normal (ethanol-extracted oats plus added avenacosides)) were used. Compared with a cellulose control group the oat diets in both species gave a significantly higher cholesterol content in the HDL fraction and a significantly lower liver cholesterol content. No significant differences in total plasma cholesterol, HDL-cholesterol and plasma triacylglycerols were found, however, between the groups fed on oats with different avenacoside content. The liver weight, total liver cholesterol and free liver cholesterol were also similar, whereas the liver lipid content was significantly lower in rats given the highest amount of avenacosides compared with zero or normal amounts. The tendency was the same in gerbils. Thus, the oat saponins had only minor effects on lipid metabolism in gerbils and rats.

Dose-response effects of boiled carrots and effects of carrots in lactic acid in mixed meals on glycaemic response and satiety

OBJECTIVE

To evaluate the effect of dosage on the metabolic response to vegetables added to a mixed lunch meal, and to relate the amounts to the tripartite plate model. Carrots were chosen as an example, and the carrots were blanched, frozen and boiled to include possible effects of processing and cooking. The effects of carrots steeped in lactic acid, as produced at fermentation, were also studied.

DESIGN

The test meals with carrots, and the control meal without vegetables, were balanced regarding energy (2000 kJ) and digestible carbohydrates (60 g) and similar in fat (17 g) and protein (16-19 g) content. The carrot portions of 100, 200 and 300 g contained 2.9, 5.8 and 8.7 g dietary fibre respectively. The meals were served in the morning after an overnight fast and in random order. Blood samples for the analysis of blood glucose, plasma insulin and C-peptide were collected and satiety was graded until 210 min postprandially.

SETTING

The study was performed at the research laboratory, Dalby Health Sciences Centre (primary care).

SUBJECTS

The 10 healthy, male volunteers, around 40 years of age, were recruited at random from the district's population list. None dropped out.

RESULTS

The larger the carrot portion the lower were the glucose and insulin/C-peptide responses and the higher the satiety scores. The minimum amount causing significant effects was 200 g. According to the plate model, 200 g of boiled carrots was the most that could be included on half the plate. Addition of lactic acid to 200 g carrots augmented the effects on satiety scores and hormonal response.

CONCLUSIONS

The addition of generous amounts of vegetables to a mixed meal improves the metabolic response.

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)

Food properties affecting the digestion and absorption of carbohydrates

Carbohydrate foods differ considerably in their effects on postprandial glucose and insulin responses. Qualitative differences among starchy foods are particularly intriguing because of the dominance of starch in human diets. This paper focuses on food properties in cereal (eg, pasta, bread, Arepas, and porridge) and legume products (eg, red kidney beans and lentils) that affect metabolic responses to starch. Studies in healthy subjects have found that postprandial blood glucose and insulin responses are greatly affected by food structure. Any process that disrupts the physical or botanical structure of food ingredients will increase the plasma glucose and insulin responses. The glycemic responses to bread products were reduced by the use of ingredients with an intact botanical or physical structure or a high amylose content or by enrichment with viscous dietary fiber. However, the important of a moderate increase in the amylose-amylopectin ratio and the naturally occurring levels of viscous cereal fiber is less clear. The rate of starch digestion in vitro was shown to be a key determinant of metabolic responses to most products. Assuming the sample preparation mimics chewing, in vitro enzymic procedures can be used to facilitate ranking. One such procedure, based on chewed rather than artificially disintegrated products, was recently developed and correlates well with glycemic and insulinemic indices for several starchy foods.

Nutritional classification and analysis of food carbohydrates

Dietary guidelines for Western countries encourage a considerable increase in carbohydrate intake. Because of new developments regarding nutritional properties of various food carbohydrates, these guidelines should include more precise recommendations of the carbohydrate composition. Small-intestinal digestibility is, nutritionally, the most important property of food carbohydrates. This was recognized early by British scientists, who differentiated between "available" and "unavailable" carbohydrates. Dietary fiber is generally defined as undigestible polysaccharides and lignin. Resistant starch is a newly discovered undigestible component included in such fiber definition, although current analysis methods do not recover all forms of resistant starch. The term "complex carbohydrates" has been used to mean digestible polysaccharides, ie, starch, in the United States, and to mean all polysaccharides, ie, both starch and nonstarch polysaccharides, in Europe. The term's usefulness is questionable because chain length of digestible carbohydrates is not related to specific nutritional advantages.

Effects of different vegetables in mixed meals on glucose homeostasis and satiety

Different vegetables--carrots, peas, Brussels sprouts and spinach--were added to a typical Swedish lunch test meal in portions of 96-164 g. The test and the control meals without vegetables were balanced with respect to digestible carbohydrates (59.7 g) and energy (2000 kJ, 475 kcal), and as far as possible also concerning protein and fat. The added vegetables contained 4.4 g dietary fibre. The meals were prepared by microwave heating and served in the morning after an overnight fast to 10 healthy, male volunteers. Postprandial blood glucose, plasma insulin and C-peptide levels were measured at regular intervals until 210 min. The satiety was graded on a simple scale of 1-10. The meal with spinach elicited significantly lower insulin and C-peptide responses than the control meal, but no significant differences in glucose response or satiety were observed. The other vegetables tested showed no significant effects either on glucose and hormonal responses or on satiety.

Incomplete digestion of legume starches in rats: a study of precooked flours containing retrograded and physically inaccessible starch fractions

The digestibility of starch in precooked flours from green coat lentils (Lens culinaris Medik) and red kidney beans (Phaseolus vulgaris L.) was investigated by balance experiments using rats treated with antibiotics to suppress hind-gut fermentation. The legume preparations were rich in intact cells filled with denaturated starch and contained retrograded amylose. Between 8% (beans) and 11% (lentils) of the total starch ingested appeared in the feces, indicating a relatively low starch digestibility. Red bean flours of two different particle sizes were similarly digested. Sixty percent of the fecal starch in the bean-fed animals and 70% in the lentil-fed group was retrograded amylose. The in vitro indigestible starch content of the flours was evaluated with three different methods that gave rather different values. The retrograded amylose fraction, measured after alkaline treatment of a dietary fiber residue obtained by enzymic digestion, was quantitatively recovered in the feces. None of the procedures gave accurate estimates of the total in vivo indigestible starch. Fecal excretion of starch in rats not treated with antibiotics indicated that the indigestible starch in lentils was less susceptible to fermentation than that in the red bean preparations.

Variation in dietary fibre, beta-glucan, starch, protein, fat and hull content of oats grown in Sweden 1987-1989

Samples of oat groat from cultivars grown in Sweden during 3 years (1987-1989, 50 samples/year) were investigated. On an average, the kernels contained 15.9% protein, 7.0% fat, 9.7% dietary fibre and 63.2% starch (% of dry matter). The coefficient of variation was highest for fat (26%) and lowest for starch (7%). The thousand kernel weight was on average 34.7 g. The content of dietary fibre and fat was significantly negatively correlated and the starch positively correlated with the thousand kernel weight. The samples contained mean (and range) 9.7% (5.0-13.4) total dietary fibre, 3.5% (2.0-5.0) soluble dietary fibre, and 4.6% (3.5-5.7) beta-glucan. The beta-glucan content was significantly positively correlated with insoluble and total dietary fibre as well as with the fat content, and significantly negatively correlated with starch.

Small intestinal peptidases and disaccharidases in rats with acute uremia

Acute uremia was induced in rats with temporary clamping of the left renal pedicle and contralateral nephrectomy. Jejunal peptidase activities (aminopeptidase N, dipeptidyl peptidase IV and aminopeptidase A), disaccharidase activities (maltase, sucrase, lactase and trehalase) and morphology were studied. A significant (p less than 0.05) increase in aminopeptidase N activity and a positive correlation between aminopeptidase N activity and serum urea was found in the uremic rats. The other peptidase activities showed a slight increase in the uremic rats. A shortening of the microvilli of the small intestinal epithelial cells in the uremic rats was seen by electron microscopy. The disaccharidase activities was unaltered. This study shows the presence of functional alterations in the small intestine in rats with acute uremia. The observations are also compatible with different regulation mechanisms for the brush border peptidases and disaccharidases.

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.

Comparison of glycemic response and insulin requirements after mixed meals of equal carbohydrate content in healthy, type-1, and type-2 diabetic man

The postprandial insulin requirements after three mixed meals of equal carbohydrate and energy content were assessed in 10 type-1 and 12 type-2 diabetics by a glucose-controlled insulin infusion system. These were compared with the glycemic response to the same meals of 10 healthy individuals (glycemic index). In type-1 diabetics, we found the highest insulin requirements after consumption of a continental breakfast (low fibre, low protein, high fat). Ten percent less insulin was infused after milk (low fat, high protein) and 30% less after an English breakfast (high fibre, high protein). Type-2 diabetics showed no significant differences in insulin requirements between the three test meals. The glycemic response in healthy individuals had no relation to these insulin requirements. Continental and English breakfast had a similar glycemic effect, whereas milk produced only 30% of the blood glucose response observed after the continental breakfast. These results indicate that neither the carbohydrate content (exchange lists) nor the glycemic index enable prediction of postprandial insulin requirements in insulin-deficient diabetes. For this purpose, we propose the insulin-need index, elaborated by testing whole meals in closed-loop experiments with type-1 diabetics.

Dietary fibre enrichment, blood pressure, lipoprotein profile and gut hormones in NIDDM patients

The influence of a beet-fibre enriched diet (mean 40 g FibrexR, 27 g dietary fibre per day) on blood pressure, plasma lipoproteins and glycaemic control was studied in 12 non-insulin-dependent diabetic (NIDD) patients. The effect on gastrointestinal hormones was also investigated. Beet-fibre and control diets were given in randomized order for 8 weeks each. During the beet-fibre diet the systolic blood pressure decreased (P less than 0.05) and the HDL-cholesterol levels increased (P less than 0.05) compared to values before the study. There was a tendency for systolic blood pressure to be lower also in the control period, but this was not statistically significant. After both diet periods the total plasma cholesterol and triglyceride levels decreased, as well as the LDL/HDL ratio. Blood glucose levels--fasting or postprandial--and glycosylated haemoglobin were not affected during the two different diet periods. In obese NIDD patients, however, the postprandial insulin levels were lower after the beet-fibre diet compared to the control diet. This subgroup also showed lower fasting values of pancreatic polypeptide and motilin were recorded for the obese patients after the fibre-rich period compared to before the study. Further, increases in postprandial motilin levels, 60-180 min, were found after the fibre-rich period. Investigations with reference to an entero-hormonal mechanism by measuring neurotensin and peptide YY did not show any variations between the diet periods.

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.

Fermentation of oat fiber in the rat intestinal tract: a study of different cellular areas

Intestinal fermentation of dietary fiber from oat husk, bran, and white flour and a commercial oat bran was investigated through balance experiments in rats. Both solubility and monomeric composition of the fiber differed widely. Fiber from husk was only 0.5% soluble and nearly completely resistant to fermentation whereas fiber from bran (38% soluble) and white flour (24% soluble) was more fermentable (62% and 55% of the intake, respectively). Fiber from commercial bran (37% soluble) was most extensively fermented; only 19% of the fiber could be detected in feces. The fecal dry weight with the husk in the diet was significantly (p less than 0.001) higher than that for the other preparations. Most of the fecal dry weight increment for husk (approximately 95%) could be accounted for as fiber whereas only 45-65% of the increment was undergraded fiber for the other preparations. An additional 20-30% could be explained by protein and approximately 15% by fat with these preparations.

Degree of starch gelatinization, digestion rate of starch in vitro, and metabolic response in rats

Glycemic response after ingestion of starchy foods varies. Starch in many common ready-to-eat foods is only partly gelatinized. In view of this, the relationships among degree of starch gelatinization, in vitro digestion rate, and in vivo metabolic response in rats were studied. Wheat starch with different degrees of gelatinization was used in the experiments. Plasma glucose and insulin responses as well as the rate of in vitro hydrolysis with alpha-amylase were strongly correlated to the degree of starch gelatinization (r = 0.88, r = 0.90, and r = 0.96, respectively). Plasma glucose and insulin responses were also positively correlated to the rate of hydrolysis with alpha-amylase in vitro (r = 0.98 and r = 0.76, respectively). These results suggest that the degree of starch gelatinization is an important determinant both for the rate of starch hydrolysis in vitro and for the metabolic response in vivo.

Effects of four meals with different kinds of dietary fibre on glucose metabolism in healthy subjects and non-insulin-dependent diabetic patients

The effects of four mixed meals on glucose metabolism were studied during a 4-h period in 12 healthy women and in 13 women with non-insulin-dependent diabetes. Three test meals containing different types of dietary fibre in realistic amounts (cereal, leguminous and mixed-fibre), and one control meal were prepared. Each meal was calculated to contain 2.1 MJ (500 kcal) and the energy distributions of protein, fat and carbohydrate (by difference) were 15, 29-31 and 56-58 per cent, respectively. Results of analyses of the mixed meals, performed after the clinical study, showed unexpectedly large deviations from the calculated values regarding digestible carbohydrates in the leguminous meal. In the healthy group the blood glucose concentrations after the four meals did not differ significantly. In the diabetic group the area under the curve of blood glucose values was significantly smaller after both the leguminous meal and that containing mixed dietary fibre than after the control meal (P less than 0.001). There were also significant differences in blood glucose between the cereal meal and the leguminous and mixed-fibre meals (P less than 0.001), and between the leguminous meal and the mixed-fibre meal (P less than 0.05). In the healthy group the insulin response was significantly lower after the leguminous meal than after the control meal (P less than 0.05) whilst the diabetic group showed lower insulin responses after all the high-fibre test meals. Serum triglycerides, cholesterol and HDL cholesterol were similar after the different meals. The lower content of digestible carbohydrates, especially in the leguminous meal, complicates the interpretation of the results.(ABSTRACT TRUNCATED AT 250 WORDS)

Dietary fiber decreases fasting blood glucose levels and plasma LDL concentration in noninsulin-dependent diabetes mellitus patients

Realistic high-fiber and regular low-fiber diets were given for 8 wk each to noninsulin-dependent diabetes mellitus (NIDDM) patients whose diabetes was being controlled satisfactorily by diet alone. The purpose of the study was to evaluate the metabolic effects of dietary fiber without changing energy intake or proportions of protein, fat, and carbohydrates. The high-fiber diet induced lower fasting blood glucose levels (p less than 0.01) and decreased the ratio of low-density lipoproteins to high-density lipoproteins (p less than 0.025); no difference was found in HbA1c between the two diet periods. Continuous glucose monitoring also showed a difference in fasting glucose levels that remained after identical low-fiber test meals. The incremental glucose responses did not differ. The fasting and incremental postprandial levels of insulin, C-peptide, glucagon, and somatostatin did not change, whereas the mean triglyceride concentrations were lower after the high-fiber diet. The results suggest a beneficial effect of dietary fiber in the metabolic control of NIDDM.

Effects of leguminous seeds in a mixed diet in non-insulin-dependent diabetic patients

The effects of moderate addition of leguminous seeds to a mixed diabetic diet were evaluated in 15 inadequately controlled patients with non-insulin-dependent diabetes mellitus. A control diet and a diet with an increased content of peas and beans (leguminous diet) were given consecutively for a 3-week period each on a metabolic ward. Seven of the patients started with the control diet and 8 with the leguminous diet. On an energy basis the diets comprised 20% protein and 33-34% fat, the ratio between polyunsaturated and saturated fatty acids was 1.4. The analysed dietary fibre contents of the control and leguminous diets were 24 and 37 g/day per 6.7 MJ (1,600 kcal) respectively. The content of digestible carbohydrates was similar in the 2 diets. The mean body weight did not differ after the 2 dietary treatment periods. All patients showed improved glucose control during treatment irrespective of the type of diet given. The fasting blood glucose concentration on admission was 14.3 +/- 0.9 mmol/l (mean +/- SEM). This value had decreased to 9.9 +/- 0.8 during the last week of the control period and to 9.7 +/- 0.6 during the last week of the leguminous diet period. The mean postprandial glucose concentration at 3 pm was significantly lower during the leguminous diet period. The mean urine glucose excretion was significantly lower during the leguminous diet period. The fasting serum lipid concentrations decreased during treatment with each diet, but there were no significant differences between these values at the end of the 2 diet treatment periods.(ABSTRACT TRUNCATED AT 250 WORDS)

Rye products in the diabetic diet. Postprandial glucose and hormonal responses in non-insulin-dependent diabetic patients as compared to starch availability in vitro and experiments in rats

Rye flakes, rye bread and white wheat bread were given as suspensions to rats and in standardized breakfast meals to non-insulin-dependent diabetics. In both cases the postprandial glucose response was lower after rye bread than after wheat bread. A larger amount of starch remained in the stomach of the rats 15 min after ingesting rye bread compared to wheat bread, indicating that delayed gastric emptying may be one factor explaining the lower response after rye bread. Although the incremental postprandial glucose areas after rye flakes and wheat bread were similar, the rate of decrease of the glucose curve was slower after flaked rye. This would point to a prolonged absorption of some starch in the rye flakes, also indicated by higher late immunoreactive insulin (IRI) values after that product. In the rats the content of starch in the stomachs 15 min after feeding was higher after rye flakes compared to wheat bread. In vitro incubations with alpha-amylase showed lower availability of the starch in rye flakes than in the breads, indicating that several factors may contribute to the differential postprandial glucose response after the wheat and rye products. The levels of insulin, C-peptide, gastric inhibitory polypeptide (GIP), glucagon, somatostatin, triglyceride and glycerol were followed after the breakfast meals. No pronounced differences of these parameters were seen. However, wheat bread gave significantly higher glucagon and GIP responses than did rye flakes. In conclusion, the absorption pattern and metabolic response after rye bread seems preferable to that after wheat bread. The flaked rye on the other hand was not effective in reducing postprandial glycaemia despite a lower availability of starch in vitro.

Enzyme resistant starch fractions and dietary fibre

Starch fractions that are more or less enzyme resistant may behave like dietary fibre, both physiologically and analytically. Ungelatinized granules from potatoes, high amylose maize and green bananas are poorly digested. Starch made resistant to amylase due to new covalent bindings, formed at heat treatment or present in starch derivatives used as food additives, may also be more or less undigestible. "Resistant starch" present in bread and corn flakes is probably retrograded amylose. It is undigestible in the small intestine, but readily degraded by the large bowel microflora. Amylose-lipid complexes seem to be completely absorbed in spite of their resistance to amylase degradation in vitro. Since undigestible starch fractions behave physiologically like non-starch polysaccharides, they should be included in the dietary fibre concept. "Resistant starch" is analysed as glucose based fibre with all current methods except one, which includes an initial DMSO solubilization step.

Definition and analysis of dietary fibre

The definition of dietary fibre as "non-starch polysaccharides plus lignin", that has now been widely accepted, is chemically more distinct than earlier definitions, but still implies some difficulties in its demarcation. In practice, analytical problems and limitations are important, since definition and analysis of dietary fibre are closely related. The delimitation towards more or less undigestible starch fractions, highly soluble polysaccharides, oligosaccharides, and undigestible protein is discussed, as well as phytate, tannins and some other components. Methods for analysis of dietary fibre are based on one or more of three different principles: 1) Weighing after removal of non-fibre components, 2) Colorimetric carbohydrate determinations 3) Specific determination of monomeric constituents by gas-liquid chromatography (GLC) or high performance liquid chromatography (HPLC). Gravimetric methods, using enzymatic degradation of protein and starch, are generally preferred for assay of total dietary fibre, or soluble and insoluble fibre separately. Colorimetric methods are used mainly for determining uronic acids as a measure of pectins. Detailed methods usually employ GLC determination of monomers after acid hydrolysis, but HPLC appear to develop as a convenient alternative. Uronic acids are determined separately by colorimetry or decarboxylation, and lignin usually as Klason lignin, i.e. acid insoluble material.

Dietary fibre--definition, chemistry and analytical determination

Dietary fibre includes non-starch polysaccharides and lignin that are not digested or absorbed in the human small intestine. It contains a mixture of chemically complex polysaccharides. Lignin is a highly cross-linked complex polymer of phenylpropane units. The plant cell wall is the main source of dietary fibre and its structure is reviewed briefly. The structure of the main dietary fibre polysaccharides is then summarized. The demarcation between starch--the main digestible polysaccharide--and dietary fibre presents some problems due to more or less enzyme resistant starch fractions that occur naturally or are formed with processing. "Resistant starch" formed during baking passes through the small intestine in the rat and, probably, in man and is fermented in the colon. It should therefore also be regarded as dietary fibre. Methods for dietary fibre determination fall into two categories: gravimetric methods, weighing the dietary fibre after removal of other components; component analysis methods, determining monomeric composition of fibre polysaccharides (preferably by gas-liquid chromatography) supplemented with a gravimetric lignin determination and separate assay of uronic acid components (pectin). Recently developed enzymatic gravimetric methods are most convenient for the assay of total dietary fibre or water soluble and insoluble fibre separately, whereas component analysis is required for determining the dietary fibre composition.

Fermentation of dietary fibre in the intestinal tract: comparison between man and rat

1. The breakdown and faecal bulking capacity of dietary fibre preparations from wheat bran, apple, cabbage, carrot, and guar gum were compared in man and rat. 2. The degradation of the fibre showed good correlation between man and rat (r 0.99, regression coefficient 0.86). Wheat bran was the least well-digested, 66 and 59% of the neutral sugars being excreted in faeces of man and rat respectively. The breakdown of the fibre in apple, cabbage, carrot and guar gum was more complete and 4-29% of the neutral sugars were recovered in faeces. 3. The main dietary fibre constituents in each preparation were degraded to a similar extent in man and rat. The main dietary fibre constituents of apple, carrot, cabbage and guar gum were almost completely degraded. Of the xylose in wheat bran 45% (man) and 48% (rat) were recovered in faeces. However, the percentage excretion of glucose and arabinose from bran was higher in man. 4. A faecal glucan other than cellulose was identified in human faeces after guar gum, and has been provisionally identified as starch. No such glucan occurred in rat faeces. 5. A good correlation between the faecal bulking capacity in man and rat was seen (r 0.97, regression coefficient 0.56). Wheat bran had the best bulking capacity, while that of apple, cabbage, carrot and guar gum was less pronounced. Faecal bulking was inversely related to the amount of fibre which was water-soluble in each preparation. 6. It is concluded that this rat experimental model is useful for the prediction of fermentative breakdown and bulking capacity of dietary fibre in man. However, more comparative studies are needed to evaluate animal experiments regarding other physiological effects of dietary fibre.

Reduced glycemic response to beet-fibre meal in non-insulin-dependent diabetics and its relation to plasma levels of pancreatic and gastrointestinal hormones

Standardized breakfasts with or without beet-fibre were given, in random order, to non-insulin-dependent diabetics. The blood glucose levels were monitored continuously and hormonal responses were determined at regular intervals for 3 hr. After the beet-fibre breakfast including 10.8 g dietary fibre from the sugar beet, the glucose plateau level and the area below the curve were lower than after the control meal. The rate of glucose decrease was also slower after the beet-fibre meal. There were no notable differences with regard to the plasma levels of insulin, C-peptide or glucagon. The gastric inhibitory polypeptide response was greater during the first part of the curve, while the somatostatin response after the beet-fibre meal displayed a significantly larger total area below the curve. The results suggest that the diminished glycemic response after the beet-fibre meal is associated with an increased response of somatostatin, giving a reduced glucose absorption and a delayed gastrointestinal transit time.

Dietary fibre fermentation in the rat intestinal tract: effect of adaptation period, protein and fibre levels, and particle size

1. The fermentative breakdown of one resistant type of dietary fibre (wheat bran) and one easily-fermented fibre (low-methoxyl pectin) was studied with respect to the length of the adaptation period and fibre level in the diet. The breakdown of the resistant fibre was also studied regarding the protein level in the diet and particle size of the fibre. 2. Prolongation of the adaptation period from 4 to 18 d decreased the faecal dry weight considerably. The excretion of dietary fibre however, was similar, whereas a decrease in faecal nitrogen excretion could be seen. 3. A level of dietary protein of less than 50 g/kg impaired the fermentation of wheat-bran fibre, whereas a level higher than 100 g protein/kg did not further increase the degree of fermentation of the fibre. 4. The particle size did not change the fermentability of the fibre, equal amounts of the main components of coarse and milled bran being excreted in faeces. 5. Two different levels of wheat-bran fibre (48 and 96 g/kg) in the diet did not influence the fibre breakdown. Similar results were obtained with two levels of fibre from low-methoxyl pectin (42 and 84 g/kg), but a tendency towards a decreased percentage of faecal excretion of uronic acids was seen at the lower level of low-methoxyl pectin.

Bulk laxatives: their dietary fibre composition, degradation, and faecal bulking capacity in the rat

The intestinal dietary fibre degradation and faecal bulking capacity of various bulk laxatives were investigated by means of balance experiments on rats. Nitrogen, fat, and mineral excretion in faeces was also studied. The dietary fibre content of the various bulk laxatives was quite different (in g/kg dry matter): ACO fibre tablets (barley and citrus pulp), 451; Fiberform (wheat bran-based), 817; Inolaxol (sterkulia gum), 696; and Vi-Siblin (ispaghula husk), 533. The increase in faecal dry matter per 1 g dietary fibre was similar with ACO fibre tablets, Fiberform, and Vi-Siblin. Inolaxol gave a significantly (p less than 0.001) higher faecal dry-weight increment, mainly due to an increased mineral excretion. Of the dry-weight increment, 59-82% constituted undegraded dietary fibre. Thus, 68-97% of the fibre passed through the gastrointestinal tract without being degraded. All the bulk laxatives caused a similar increase in the faecal N content, whereas the increase in faecal lipids was most pronounced with Vi-Siblin. The water-holding capacity of faeces was more pronounced with Inolaxol and Vi-Siblin than with ACO fibre tablets and Fiberform.