Article

Metabolic Responses to Venezuelan Corn Meal and Rice Bran Supplemented Arepas (Breads)

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Abstract

Cereal Chem. 82(1):77-80 The metabolic responses to South American foods remain to be determined. Using glycemic index (GI) and insulinemic index (II) values as references for therapeutic potential of foods, this study investigated the glucose responses to a typical Venezuelan corn bread (arepa) and to an arepa supplemented with rice bran. Adding rice bran to the bread increased the content of resistant starch and dietary fiber measured as total, soluble, and insoluble dietary fiber. It also increased the protein content of the arepa. Three meals, white wheat bread, 100% corn meal arepa, and an arepa supplemented with 20% rice bran, were administered within a one-week period. Available starch in the foods was determined to provide 50 g of available carbohydrate per meal. To calculate the indices, bread was used as the reference. The GI and II of the two arepa meals were significantly smaller than the GI and II of white wheat bread, although the differences between the two types of arepas were not significant. It is concluded that Venezuelan arepas (corn meal bread) may have potential health benefits and that the presence of 20% rice bran in the arepa meal did not produce a significant improvement in the glucose response. Due to the presence of antioxidant elements in the supple- mented arepa and its higher protein, dietary fiber, and resistant starch content, it may have a potential preventive effect against the development of other pathologies.

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The importance of the amylose: amylopectin ratio in the postprandial glycemic and insulinemic responses to corn was studied in food products that might realistically be consumed. Healthy subjects were given test meals in the form of arepas made from ordinary (25% amylose) or high amylose (70% amylose) corn flour. The ordinary corn meal contained 45 g of potentially available starch. To exclude the possible influence of a lowered content of potentially available starch due to formation of resistant starch in the high amylose product, this product was evaluated at two levels and included either on the basis of potentially available starch (45 g) or total starch (including resistant starch) (45 g, i.e., 29 g potentially available starch), respectively. The rate of starch hydrolysis, measured in vitro employing a method based on chewing, was studied. In addition, the content of in vitro resistant starch was analyzed in all products. The meals containing high amylose corn flour produced lower areas under the glucose and insulin response curves (57 and 42% lower, respectively) than did the meals containing ordinary cornmeal. This could not be explained by a lower amount of potentially available starch. No differences were noted when subjects consumed the two high amylose meals of arepas, despite 36% lower potentially available starch in one of the meals. The rate of starch hydrolysis measured in vitro was slower in the high amylose corn products than in the ordinary corn product. Resistant starch in the ordinary product was 3 g/100 g dry matter, vs. approximately 20 g/100 g dry matter in the high amylose products. We concluded that high amylose corn products have a potential to promote favorably low metabolic responses and high resistant starch contents.
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To define those patients most likely to benefit from the hypolipidemic effect of low-glycemic-index (GI) traditional starchy foods, 30 hyperlipidemic patients were studied for 3 mo. During the middle month, low-GI foods were substituted for those with a higher GI with minimal change in dietary macronutrient and fiber content. Only in the group (24 patients) with raised triglyceride levels (types IIb, III, and IV) were significant lipid reductions seen: total cholesterol 8.8 +/- 1.5% (p less than 0.001), LDL cholesterol 9.1 +/- 2.4% (p less than 0.001), and serum triglyceride 19.3 +/- 3.2% (p less than 0.001) with no change in HDL cholesterol. The percentage reduction in serum triglyceride related to the initial triglyceride levels (r = 0.56, p less than 0.01). The small weight loss (0.4 kg) on the low-GI diet did not relate to the lipid changes. Low-GI diets may be of use in the management of lipid abnormalities associated with hypertriglyceridemia.
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To study the postprandial effects of changing the amylose-to-amylopectin ratio (Am:Ap) in the starch fraction of a meal, male volunteers were given hot mixed lunches ( 13% of energy as protein, 24% as fat, 6% as mono- and disaccharides, and 57% as polysaccharides) in which Am:Ap was either 0:100 or 45:55. The increase in Am:Ap resulted in a change in the shape of the glucose and insulin responses in the blood with significantly lower initial responses but a small increase for glucose and a decrease for insulin if averaged over the 6 h of the study. The rises in the concentration of free glycerol and free fatty acid that occurred after an initial drop were stronger at low Am:Ap. High-Am:Ap meals induced more satiety up to 6 h postprandially. There was no effect of Am:Ap on postprandial triacylglycerol in the blood or on breath hydrogen except for a weak trend toward a higher concentration at 6 h after the high-Am:Ap meals.
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In a modified method for measuring Resistant Starch (RS) in dietary fiber residues all operations for obtaining fiber residues and determination of RS were performed in a 50 mL centrifugation tube. This minimized error sources and simplified previous methodology.
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A rapid enzymic method for starch analysis, especially in cereal products, is presented. One person can analyze 30 samples per day. The method includes a 15 min gelatinization step in a boiling water bath in the presence of a thermostable α-amylase, a 30 min amyloglucosidase incubation of a subsample, and subsequent determination of glucose with a glucose oxidase/peroxidase reagent. The method was evaluated by analysis of the starch content in various raw and industrially processed wheat samples. The method showed high precision (CV=0.6–1.0%) and accuracy. Some factors which might affect the enzymic availability of starch and thus its recovery in the analysis are evaluated and discussed. Eine schnelle Methode Zur Bestimmung von Stärke. Es wird eine schnelle enzymatische Methode zur Bestimmung von Stärke, insbesondere in Getreideprodukten, vorgestellt. Eine Person kann 30 Proben am Tag untersuchen. Die Methode umfaße eine 15 min lange Verkleisterung in Gegenwart einer thermostabilen α-Amylase in einem kochenden Wasserbad, eine 30 min lange Behandlung eines Teiles der Probe mit Amyloglucosidase und eine nachfolgende Bestimmung der Glucose mit einem Glucoseoxidase/Peroxidase-Reagens. Die Beurteilung der Methode erfolgte durch die Bestimmung des Stärkegehaltes in verschiedenen rohen und industriell verarbeiteten Weizenproben, sie zeigte große Genauigkeit (CV = 0,6–1,0%). Einige Faktoren, welche die enzymatische Verfügbarkeit von Stärke und somit ihre Erfassung bei der Bestimmung beeinflussen, werden diskutiert.
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Heat-processed foods can contain appreciable amounts of resistant starch (RS) that has the ability to survive prolonged incubation with a-amylase and other amylolytic enzymes. The occurrence of RS has important implications for dietary fibre (DF) determination and, possibly, for human bowel physiology also. Studies using cereal and potato starches have identified three key factors that influence yields of RS after heat-processing, i.e. amylose content, processing temperature and water content. The highest yields of RS (20–34% of total dry weight) were obtained from amylomaize starches, either raw or processed, and from amylopectin starches (32–46% RS) after incubation with α-(1→6)-debranching enzyme (pullulanase) followed by heat-processing. In contrast, the lowest yields of RS (0⁗2–4⁗md2%) were obtained from intact (i.e. non-debranched) amylopectin starches, with or without heat-processing. Yields of RS from wheat starch were affected primarily by processing temperature, reaching levels of about 9% in a single cycle of autoc1aving at 134°C with excess water and subsequent cooling (cf. levels of less than 1% in uncooked wheat starch) and higher levels still (about 15%) after five repeated cycles of autoclaving and cooling. A similar increase in yields of RS was seen in dilute (1%) starch suspensions that were subjected to repeated cycles of heating to 100°C, followed by cooling and storage. The time of storage after gelatinisation was only important in these dilute systems: levels of RS in freshly prepared concentrated starch gels (typically 57–67% H2O) or in white bread did not alter significantly on storage.
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A method for resistant starch (RS) determination in food and food products is proposed. The main features are: removal of protein; removal of digestible starch; solubilization and enzymatic hydrolysis of RS; and quantification of RS as glucose released. Stomach and intestine physiological conditions (pH, transit time) were approximately simulated. All operations were performed in a 50ml centrifuge tube. Reference materials and food products were analysed by three laboratories. Statistical analysis included repeatability and reproducibility. This procedure is quite satisfactory for starchy foods containing appreciable quantities of RS and it may be useful for nutritional labelling of foodstuffs. For samples containing ⩽ 1% RS, differences are not significant and they can be considered as foods with a negligible RS content.
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Food carbohydrates consist of mono-, di-, oligo- and polysaccharides, the latter composed of starch and non-starch polysaccharides (NSP). The glycaemic response to both sugars and starches is dependent on the types of sugars present and the form of the starches, and ‘complex carbohydrates’ do not necessarily produce slower or lower glycaemic responses than the sugars. Carbohydrates not absorbed in the small intestine are fermented more or less extensively by the large intestinal microflora. There is a fundamental difference nutritionally between digestible and undigestible (‘unavailable’) carbohydrates. NSP, resistant starch (RS) and oligosaccharides are the main forms of undigestible carbohydrates. Dietary fibre is generally conceived as more or less synonymous with ‘unavailable’ carbohydrates. The nutritional effects of dietary fibre are related to its undigestibility in the small intestine, and to the physical and chemical properties of its constituent polysaccharides. Food structures built of dietary fibre as plant cell-walls, and also of other food components, are increasingly recognized as nutritionally important. Food databases should include as much specific and detailed information as possible on food carbohydrates. For food labelling, carbohydrates have to be divided into a number of nutritionally meaningful classes. A first classification should then aim at differentiating the digestible and undigestible carbohydrates, i.e. dietary fibre.
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From the mid-1970s several groups realized progressively that the same amounts of carbohydrates in different foods produce quite different blood glucose curves after ingestion. The glycaemic index (GI) was introduced by Jenkins to express the rise of blood glucose after eating a food against a standard blood glucose curve after glucose (or white bread) in the same subject. The GI ranges from about 20 for fructose and whole barley to about 100 for glucose and baked potato. A table is given of representative GI values. There appears to be no general correlation between GI and per cent resistant starch in foods. Questions about methodology for GI are discussed and the factors in food that affect glycaemic response are briefly reviewed. The GI is affected by the physical form of a food, by processing and by associated fat in the food, which reduces the GI, presumably by delayed gastric emptying. As a rule the degree of insulin response to carbohydrate-containing foods is similar to the glycaemic response. Most investigators have found that the GI of a meal of mixed foods can be predicted from the (weighted) GI of its constituent foods. The GI concept is proving useful in dietary design for the management of diabetes mellitus, especially the non-insulin-dependent type. It may prove useful for prevention of diabetes and perhaps also in pre-event meals for athletes, as a factor in dental cariogenesis, in determining satiety, and conceivably regular low GI foods could delay ageing by reducing glycosylation of body proteins.
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To study the postprandial effects of changing the amylose-to-amylopectin ratio (Am:Ap) in the starch fraction of a meal, male volunteers were given hot mixed lunches (13% of energy as protein, 24% as fat, 6% as mono- and disaccharides, and 57% as polysaccharides) in which Am:Ap was either 0:100 or 45:55. The increase in Am:Ap resulted in a change in the shape of the glucose and insulin responses in the blood with significantly lower initial responses but a small increase for glucose and a decrease for insulin if averaged over the 6 h of the study. The rises in the concentration of free glycerol and free fatty acid that occurred after an initial drop were stronger at low Am:Ap. High-Am:Ap meals induced more satiety up to 6 h postprandially. There was no effect of Am:Ap on postprandial triacylglycerol in the blood or on breath hydrogen except for a weak trend toward a higher concentration at 6 h after the high-Am:Ap meals.
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There is controversy regarding the clinical utility of classifying foods according to their glycemic responses by using the glycemic index (GI). Part of the controversy is due to methodologic variables that can markedly affect the interpretation of glycemic responses and the GI values obtained. Recent studies support the clinical utility of the GI. Within limits determined by the expected GI difference and by the day-to-day variation of glycemic responses, the GI predicts the ranking of the glycemic potential of different meals in individual subjects. In long-term trials, low-GI diets result in modest improvements in overall blood glucose control in patients with insulin-dependent and non-insulin-dependent diabetes. Of perhaps greater therapeutic importance is the ability of low-GI diets to reduce insulin secretion and lower blood lipid concentrations in patients with hypertriglyceridemia.
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Different starchy foods produce different glycemic responses when fed individually, and there is evidence that this also applies in the context of the mixed meal. Methods of processing, and other factors unrelated to the nutrient composition of foods may also have major effects on the glycemic response. The reason for differences in glycemic response appears to relate to the rate at which the foods are digested and the many factors influencing this. The glycemic index (GI) is a system of classification in which the glycemic responses of foods are indexed against a standard (white bread). This allows the results of different investigators to be pooled. GI values also depend upon a number of nonfood-related variables. The method of calculation of the glycemic response area is most important, but the method of blood sampling and length of time of studies also may have effects. Variability of glycemic responses arises from day-to-day variation in the same subject and variation between different subjects. There is less variability between the GI values of different subjects than there is within the same subject from day to day. Therefore, the mean GI values of foods are independent of the glucose tolerance status of the subjects being tested. Potentially clinically useful starchy foods producing relatively flat glycemic responses have been identified, including legumes, pasta, barley, bulgur, parboiled rice and whole grain breads such as pumpernickel. Specific incorporation of these foods into diets have been associated with reduced blood glucose, insulin, and lipid levels. Low-GI foods may influence amino acid metabolism although the implications of these are unknown. In addition, low GI foods increase colonic fermentation. The physiologic and metabolic implications of this relate to increased bacterial urea utilization, and to the production and absorption of short chain fatty acids in the colon. The application of the GI to therapeutic diets should be in the context of the overall nutrient composition of the diet. High-fat or high-sugar foods may have a low GI, but it may not be prudent to recommend these foods solely on the basis of the GI. It is therefore suggested that the most appropriate use of the GI is to rank the glycemic effects of starchy foods which would already have been chosen for possible inclusion in the diet on the basis of their nutritional attributes, i.e. low-fat, unrefined carbohydrate.
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Twelve men consumed a diet containing 34% of calories as 70% amylose or amylopectin starch to determine if the structure of starch could influence metabolic factors associated with abnormal states. Each starch was fed to subjects for 5 wk in a crossover design. No significant differences were observed in glucose or insulin levels when a glucose tolerance was given after 4 wk on each starch. However, glucose and insulin responses were significantly lower when a meal containing amylose compared with amylopectin was consumed after 5 wk on each starch. Summation of 0.5 through 2-h levels of insulin but not glucose were significantly lower after amylose compared with levels after amylopectin. Mean fasting triglyceride and cholesterol levels were significantly lower during the period when amylose was consumed. Long-term intake of dietary amylose may be valuable in decreasing insulin response while maintaining proper control of glucose tolerance and low levels of blood lipids.
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The glycaemic index is a measure of the extent to which the carbohydrate in a food can raise the blood glucose concentration and helps to identify foods which may be beneficial to a diabetic patient. This paper reviews the results that have been obtained so far with the glycaemic index approach, the factors that affect the glycaemic response, the problems that are associated with its measurement and its value in planning diabetic diets. Individual variation and variation among individuals in glycaemic responses are also discussed.
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An investigation, aimed at determining the nature and relative utilization of carbohydrates of recently evolved high yielding varieties of rice was carried out. The amylose content and the starchâ€"iodine blue value were deter mined in relation to the cooking quality of these varieties. The rates of in vitro digestibility using a-amylase were compared. The significance of in vitro experi ments was further tested in vivo in human subjects with two of the varieties which differed greatly in in vitro o-amylolysis. These studies revealed that the amylose content in these varieties ranged from 15 to 22% of the starch. The Hamsa variety showed highest value for amylose while the amylose content of IR-8 was exceptionally low â€" 15% of its starch. The in vitro digestibility trials using pancreatic a-amylase indicated that the rate of o-amylolysis of Hamsa variety was higher compared with any other variety analyzed whereas that of IR-8 rice was markedly lower. Studies carried out with Hamsa and IR-8 varieties of rice on human subjects indicated that with Hamsa more subjects showed higher blood glucose values compared with IR-8. J. Nutr. 101: 879-884, 1971.
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Serial measurements of serum cholesterol and triglyceride (TG) concentrations were performed in diabetic men fed high-carbohydrate, high-fiber (HCF) as well as high-carbohydrate, low-fiber (HCLF) diets. Fourteen lean men were first fed control diets for 1 wk and then fed weight-maintaining HCF diets (70% carbohydrate) that were restricted in fat and cholesterol. Average insulin doses dropped from 27 U/day on control diets to 12 U/day on HCF diets and fasting plasma glucose values were 26 mg/dl lower on HCF diets. On HCF diets, serum cholesterol values were lower by 32% (64 mg/dl, p < 0.001) than values on control diets. Fasting serum TG values were slightly lower on HCF diets but average postprandial TG values were significantly lower (p < 0.001) on HCF diets than on control diets. In another study, 11 men were fed two weight-maintaining 70% carbohydrate diets in an alternating sequence; one diet was high in plant fiber (HCF) and the other was low in plant fiber (HCLF). Insulin doses averaged 20 U/day on control diets and fell to 11 U/day (p < 0.01) on HCF diets or 12 U/day (p < 0.01) on HCLF diets. Fasting serum TG values were similar on the control and HCF diets; on HCLF diets fasting serum TG values were higher by 28% (37 mg/dl) than values on control diets (p < 0.01). Incorporation of generous amounts of plant fiber into the diet prevented the hypertriglyceridemic response to these high-carbohdrate diets. These studies also indicate that dietary maneuvers can be very effective in lowering serum cholesterol values in patients with diabetes mellitus.
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The effects of acute and chronic dietary fiber (cellulose and pectin) supplementation on both intestinal glucose absorption and oral glucose tolerance were studied in rats. The effect of intraluminal fiber on intestinal glucose absorption was evaluated in perfused jejunal loops as was the effect of a single cellulose or pectin-supplemented meal on serum glucose responses to a carbohydrate load. Neither pectin nor cellulose impaired jejunal glucose absorption, but pectin did decrease serum glucose responses to an oral carbohydrate load. Chronic fiber supplementation significantly decreased intestinal glucose absorption in rats who had received for 5 wk a fiber-free diet supplemented with either cellulose (10%) or pectin (5%). Chronic supplementation with cellulose or pectin impaired intestinal glucose absorption and decreased serum glucose responses. These results suggest that differences in glucose homeostasis observed after ingestion of single high-fiber meals may be caused by viscosity-related delays in the rate of gastric emptying, whereas differences noted after chronic supplementation of dietary fiber are related to adaptive changes in the intestine.
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The determine the effect of different foods on the blood glucose, 62 commonly eaten foods and sugars were fed individually to groups of 5 to 10 healthy fasting volunteers. Blood glucose levels were measured over 2 h, and expressed as a percentage of the area under the glucose response curve when the same amount of carbohydrate was taken as glucose. The largest rises were seen with vegetables (70 +/- 5%), followed by breakfast cereals (65 +/- 5%), cereals and biscuits (60 +/- 3%), fruit (50 +/- 5%), dairy products (35 +/- 1%), and dried legumes (31 +/- 3%). A significant negative relationship was seen between fat (p less than 0.01) and protein (p less than 0.001) and postprandial glucose rise but not with fiber or sugar content.
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1. Experiments were carried out in human volunteers to investigate the mechanism by which guar gum improves glucose tolerance. 2. Guar reduced both plasma glucose and insulin responses to an oral glucose load, and delayed gastric emptying. However, there was no correlation between changes in individual blood glucose responses and changes in gastric emptying rates induced by guar. 3. With a steady-state perfusion technique, glucose absorption was found to be significantly reduced during perfusion of the jejunum with solutions containing guar, but returned to control values during subsequent guar-free perfusions. 4. Preperfusing the intestine with guar did not affect electrical measurements of unstirred layer thickness in the human jejunum in vivo.. 5. Experiments in vitro established that glucose diffusion out of a guar/glucose mixture was delayed under conditions of constant stirring. 6. We conclude that guar improves glucose tolerance predominantly by reducing glucose absorption in the small intestine. It probably does this by inhibiting the effects of intestinal motility on fluid convection.
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A two-stage perfusion technique was used to study the effect of guar gum on the inulin-accessible space and the uptake of water and glucose in rat intestine. Pre-perfusion of test loops with low concentrations of guar, dispersed in saline, modified the rate of equilibration of inulin with the mucosal fluid space during a subsequent perfusion. The glucose absorption rate in such loops was reduced at a concentration of 50 mM, but not at 100 or 150 mM glucose. Fluid absorption was inhibited by pre-treatment with guar gum at all glucose concentrations tested. These results suggest that guar forms a layer closely associated with the mucosal surface which modifies the viscosity of the immediate fluid compartment, so that its resistance to diffusion is increased by means of an unstirred layer effect.
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The rise of blood glucose in normal and diabetic subjects after meals varies markedly and depends on many factors, including the source of the carbohydrate, its method of preparation, and the composition of the total meal. Classification of carbohydrates as simple or complex does not predict their effects on blood glucose or insulin. Rapidly absorbed carbohydrates, which produce large blood glucose and insulin responses, may be in the form of both sugars and starches. Sugars added to foods have no different effect on blood glucose from those of sugars alone. The natural sugars in fruit and fruit juices raise blood glucose approximately as much as does sucrose and less than do most refined starchy carbohydrate foods. The optimum amount of sugars in the diet is not known. However, undue avoidance of sugars is not necessary for blood glucose control and is not advised because it may result in increased intakes of fat and high-glycemic-index starch.
Article
Although fiber has been increasingly recognized as an important dietary constituent, controversy and confusion still exist about the physiologic effects of fiber. Specifically, the independent ability of dietary fiber to lower serum lipid levels is controversial. The purpose of this article is to review available evidence regarding the impact of soluble fibers on serum lipid levels. Soluble fibers appear to have a greater potential to alter serum lipid levels than do insoluble fibers. Significant reduction in the level of serum total cholesterol by soluble fiber was found in 68 of the 77 (88%) human studies reviewed. Of the studies measuring low-density lipoprotein cholesterol, 41 of 49 (84%) reported significant reductions. No significant changes were reported in 43 of the 57 (75%) studies that reported high-density lipoprotein cholesterol and/or in 50 of the 58 (86%) studies that measured triglyceride levels.