Canavanine content in sword beans (Canavalia gladiata): analysis and effect of processing.

The amino acid canavanine is a potentially toxic constituent of leguminous seeds. The aim of the present study was to determine the ability of different processing methods to reduce canavanine in sword beans (Canavalia gladiata). For this purpose a method for the detection and quantification of canavanine was developed using reversed-phase high-performance liquid chromatography of the dabsylated derivatives. The recovery of canavanine using this method was 88-91%. Optimum extraction of canavanine from raw and processed beans was obtained by addition of hot water prior to overnight soaking. The results obtained with this method agree well with previously published values for raw seeds. The method is sensitive, specific and can successfully be applied to the detection of canavanine in legumes. Overnight soaking and boiling in excess water followed by decanting gave the most pronounced reduction in canavanine content (around 50%), followed by boiling and decanting excess water (34%). Roasting as used in this study and autoclaving were less effective in reducing the canavanine content.

Effect of dietary fiber on the induction of colorectal tumors and fecal beta-glucuronidase activity in the rat.

The purpose of the present study was to investigate whether three different types of dietary fiber, wheat bran, carrot fiber, and citrus pectin, influenced the induction of colorectal tumors produced by 1,2-dimethylhydrazine in rats. In all groups, the tumor yield was high (87 to 97%). In the wheat bran and carrot fiber groups, the incidence of colorectal tumors was not significantly different from that of the group fed on the fiber-free basic diet. The citrus pectin group, however, had a significantly higher incidence of colorectal tumors (p less than 0.001). An increased number of auditory duct tumors was also noted in this group. In a separate experiment, dietary pectin induced a 10-fold increase in fecal beta-glucuronidase activity but did not alter this activity in the bowel wall. It has been suggested that dietary fiber protects against the induction of colorectal tumors, but this was not the case in the experiment. It is possible that the high tumor yield made the demonstration of a weak protective effect of wheat bran impossible. The reason for the increased occurrence of tumors in the citrus pectin group is obscure and will be subjected to further investigation. Fecal beta-glucuronidase activity might be one factor of importance in the activation of the carcinogen.

Effect of two kinds of pectin and guar gum on 1,2-dimethylhydrazine initiation of colon tumors and on fecal beta-glucuronidase activity in the rat.

The effect of 5% low-methoxylated pectin, high-methoxylated pectin, and guar gum on 1,2-dimethylhydrazine initiation of colon cancer was investigated using groups of 30 rats. The growth of the rats in the different groups was very similar to that of control group fed a fiber-free diet. Both kinds of pectin increased the multiplicity of color tumors, whereas guar gum did not significantly influence carcinogenesis. Bacterial beta-glucuronidase activity in feces and colonic content was the same in pectin-fed rats and controls but significantly lower in the guar gum group. Thus, it was not related to the number of tumors in each group.

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.

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.

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.

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.

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.

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.

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.

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.

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.

Nutrient intake and health status of lactovegetarians: chemical analyses of diets using the duplicate portion sampling technique.

Six middle-aged lactovegetarians (three men and three women) collected copies of four 24-h diets using the duplicate portion sampling technique. By chemical analyses, the nutrient composition of the lactovegetarian diet was determined in detail and compared with that of a mixed Swedish diet (normal) and a vegan diet (vegan) studied previously. The nutrient composition of the lactovegetarian diet expressed per 1000 kcal represented an average between normal and vegan diets. It was in closer agreement with Swedish recommended dietary allowances than the normal Swedish diet. Thus, the lactovegetarian diet contained 35% of the energy as fat and was rich in polyunsaturated fatty acids, especially linoleic acid, which resulted in a polyunsaturated/saturated fat ratio of 0.6. The lactovegetarian diet had a cholesterol concentration only half of that of a normal diet. Protein content and amino acid composition were well above recommendations. The lactovegetarian diets contained less sucrose than normal and vegan diets, but the sum of the intake of low molecular weight carbohydrates was comparable to normal and vegan diets. Dietary fiber was three times higher than in a normal diet. Essential minerals and trace elements, ie, Ca, Mg, Na, K, Fe, Zn, Cu, Se, satisfied current requirements. The intake of vitamin B12 by the lactovegetarians was around 1.4 micrograms daily, which is below the recommendations. The intake of folates was high, 300 to 400 micrograms daily. The clinical and biochemical investigation of the subjects revealed no signs of nutritional deficiency. Their plasma lipoproteins and the blood pressures were low for their age, in agreement with observations made earlier in a group of vegans.

Nutrient intake and health status of vegans. Chemical analyses of diets using the duplicate portion sampling technique.

A strict vegetarian diet [vegan diet (VD)] was investigated. Six middle-aged vegans (three men and three women) collected copies of 24-h diets using the duplicate portion sampling technique. By chemical analyses, the nutrient composition was determined in detail and compared with corresponding figures of a normal mixed Swedish diet. In the VD 30% of the energy originated from fat compared with 40% in normal Swedish mixed diet (MD). Linoleic acid was the dominant fatty acid (60% of total fat in VD versus 8% in MD). The VD contained 24 g protein/1000 kcal compared to 30 g/1000 kcal in MD, but the intake of essential amino acids by the vegans exceeded the recommendations. Dietary fiber was about 5 times higher in the vegan diet (29 versus 6 g/1000 kcal) and sucrose similar to MD (18 versus 21 g/1000 kcal). Among the inorganic nutrients the concentration of calcium (351 versus 391 mg/1000 kcal) and sodium (53 versus 49 mmol/1000 kcal) were similar in both types of diets but the amount of potassium (56 versus 30 mmol/1000 kcal, magnesium (300 versus 110 mg/1000 kcal), iron (9 versus 6.5 mg/1000 kcal), zinc (6.5 versus 4.7 mg/1000 kcal), and copper (2 versus 0.7 mg/1000 kcal) were nearly doubled. Iodine (39 versus 156 micrograms/1000 kcal and selenium (5 versus 17 micrograms/1000 kcal) were much lower in the VD, selenium even being undetectable in several 24-h diets. The VD was rich in folic acid (301 versus 90 micrograms/1000 kcal in MD) but the intake of vitamin B12 was only 0.3 to 0.4 microgram/day (MD: 3 to 4 micrograms/day). No clinical signs of nutritional deficiency were observed in the vegans. Serum protein levels of the vegans as well as their serum lipoproteins were near the lower range of the reference group. In addition, none of the vegans was overweight and their blood pressures were low for their age.

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.

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.

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)

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.

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.

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.