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.     

The effect of various thermal processes on the glycemic response to whole grain wheat products in humans and rats

The effects of different thermal processes used to produce ready-to-eat cereals on the glycemic response to whole grain wheat were investigated in rats. The metabolic response to drum dried flour, which constitutes the major component in instant gruel and porridge, was also studied in healthy human subjects. Boiled flour was used for comparison. The degree of starch gelatinization and rate of starch hydrolysis in vitro were also measured. Incompletely gelatinized steam flaked and dry autoclaved products were digested more slowly in vitro and elicited lower glucose responses in rats compared with completely gelatinized drum dried, extrusion cooked or boiled samples. The initial glycemic response in rats was closely related to the rate of starch hydrolysis in the pepsin/alpha-amylase assay (r = 0.91, P less than 0.04). When pepsin was omitted, no significant correlation was obtained. The peak glucose, insulin and C-peptide responses in humans after breakfast meals of porridge prepared from drum dried flour and from boiled flour were similar, whereas the rate of depression of the glucose curve was more rapid after consuming drum dried porridge. It is concluded that the glycemic response to wheat products is affected by the processing conditions used. The more severe the processing conditions, the more rapid the digestion of starch.     

Rice varieties with similar amylose content differ in starch digestibility and glycemic response in humans

Three high-amylose rice varieties, IR42, IR36, and IR62, with similar chemical composition including amylose content (26.7-27.0%), were cooked under the same conditions and tested for in vitro digestibility as well as blood glucose and insulin responses in healthy human volunteers. The starch-digestion rate and the glycemic and insulin responses were the highest in IR42, followed by IR36 and, then IR62. The differences were not due to unabsorbed carbohydrate but were related to their physicochemical properties, such as gelatinization temperature, minimum cooking time, amylograph consistency, and volume expansion upon cooking. When the three varieties were cooked for their minimum cooking time, they had the same degree of gelatinization and their starch-digestion rates and glycemic responses were similar. We conclude that amylose content alone is not a good predictor of starch-digestion rate or glycemic response. Rice varieties with similar high-amylose contents can differ in physicochemical (gelatinization) properties and this, in turn, can influence starch digestibility and blood glucose response.     

Long-term intake of rice improves insulin sensitivity in mice fed a high-fat diet

ObjectiveThe aim of this study was to evaluate the effects of rice as a carbohydrate source and its molecular mechanisms on insulin resistance induced by a high-fat diet (HFD).MethodsC57 BL/6 J mice were divided into three groups and were fed a low-fat diet (LFD); a HFD (with 18% fat, 0.5% cholesterol, 51.5% w/w cornstarch and sucrose); or a HFD with rice (HFD-CR, with 18% fat, 0.5% cholesterol and 51.5% w/w rice powder) for 12 wk. In the HFD-CR diet, cooked rice powder was substituted for cornstarch and sucrose in the HFD as a carbohydrate source.ResultsHFD-CR–fed mice had significantly lower body weight, blood glucose, insulin and leptin levels and ameliorated glucose responses with decreased homeostasis model assessment-insulin resistance compared with HFD-fed mice. Hepatic mRNA levels of phosphoenolpyruvate carboxykinase and glucose-6-phosphatase were down-regulated in the HFD-CR group. The hypertrophied islet size and the decreased pancreatic mRNA expression of glucose transporter 2 in the HFD group were normalized with cooked rice consumption. Rice promoted glucose uptake by activating AMP-activated protein kinase and downstream glucose transporter 4 in the skeletal muscle.ConclusionRice consumption as a carbohydrate source might potentiate improvements in glucose uptake via AMP-activated protein kinase activation and glucose transporter 4 expression in the skeletal muscles, thereby improving insulin sensitivity.     

The relationship between translucency of rice grain and gelatinization of starch in the grain during cooking

The soaked and nonsoaked rice grains were cooked by the excess water method and the steamer method, and subjected to Ranghino's test, X-ray diffraction, and microscopic observation. The starch granules in the nonsoaked rice were gelatinized at the same time as the grains became translucent during cooking. However, when the grains of medium amylose varieties and waxy rice were presoaked, the starch granules were not fully gelatinized in the translucent grains cooked for Ranghino's cooking time. The gelatinization of starch granules proceeded faster in the soaked rice and by the excess water method than that in the nonsoaked rice and by the steamer method. The cooking time and gelatinization time correlated negatively with the water content after soaking, and positively with the amylose content in the rice grains. The japonica rices were gelatinized fully in less than 20 min when the amount of water added for cooking was adequate.     

Blood glucose lowering effects of brown rice in normal and diabetic subjects

Carbohydrate foods, which produce low glycemic responses, have been shown to be beneficial in the dietary management of chronic diseases such as diabetes and hyperlipidemia. This study determined the starch digestion rate in vitro and, in a randomised crossover design, the postprandial blood glucose response of 10 healthy and nine type 2 diabetic volunteers to brown rice compared to milled rice from the same batch and variety. The total sugar released in vitro was 23.7% lower in brown rice than in milled rice. In healthy volunteers, the glycemic area and glycemic index were, respectively, 19.8% and 12.1% lower (p?<?0.05) in brown rice than milled rice, while in diabetics, the respective values were 35.2% and 35.6% lower. The effect was partly due to the higher amounts of phytic acid, polyphenols, dietary fiber and oil in brown compared to milled rice and the difference in some physicochemical properties of the rice samples such as minimum cooking time and degree of gelatinisation. In conclusion, brown rice is a more health beneficial food for diabetics and hyperglycemic individuals than milled rice.     

Rate of starch hydrolysis in vitro as a predictor of metabolic responses to complex carbohydrate in vivo

This study was designed to determine whether the rate of hydrolysis of different starches by pancreatic amylase in vitro was proportional to the postprandial glucose and insulin response to those starches after oral ingestion. Lean young men consumed four test meals of rice containing 75 g starch: white rice, unpolished (brown) rice, ground white rice, and ground brown rice. Postprandial glucose and insulin responses were measured over 4 h and showed the following pattern: ground white rice congruent to ground brown rice greater than white rice greater than brown rice. The maximum increases in blood glucose after the four meals were brown rice 0.9 mM, white rice 1.5 mM, ground brown rice 3.3 mM, and ground white rice 3.6 mM. Samples of the cooked rices were incubated in vitro with pancreatic amylase for 30 min and the percentage starch hydrolysis determine. The relative rates of starch hydrolysis correlated very closely with the peak glucose responses: brown rice 17.6%, white rice 30.8%, ground brown rice 68.2% and ground white rice 71.8%. These results indicated that the rate of intestinal hydrolysis of starch is an extremely important determinant of the metabolic responses to a particular starch. The rate of starch hydrolysis can be determine simply by an in vitro method and should assist the design of diets for the treatment of diabetes.     

An examination of the possibility of lowering the glycemic index of oat and barley flakes by minimal processing

Differences in glycemic responses to various starchy foods are related to differences in the rate of starch digestion and absorption. In this study, the importance of the degree of gelatinization and the product thickness for postprandial glycemic and insulinemic responses to rolled oats and barley were studied in healthy subjects (5 men and 5 women). Thick (1.0 mm) rolled oats were made from raw or preheated (roasted or steamed) kernels. In addition, thin (0.5 mm) rolled oats were made from roasted or roasted and steamed (processed under conditions simulating commercial production) oat kernels. Finally, steamed rolled barley kernels (0.5 or 1.0 mm) were prepared. All thin flakes elicited high glucose and insulin responses [glycemic index (GI), 88-118; insulinemic index (II), 84-102], not significantly different from white wheat bread (P: > 0.05). In contrast, all varieties of thick oat flakes gave significantly lower metabolic responses (GI, 70-78; II, 58-77) than the reference bread (P: < 0.05). Thick barley flakes, however, gave high glucose and insulin responses (GI, 94; II, 84), probably because the botanical structure underwent more destruction than the corresponding oat flakes. We conclude that minimal processing of oat and barley flakes had a relatively minor effect on GI features compared with the more extensive commercial processing. One exception was thick oat flakes, which in contrast to the corresponding barley flakes, had a low GI.     

The effect of amylose content on insulin and glucose responses to ingested rice

We evaluated the effect of amylose and amylopectin content on the glucose and insulin responses to rice. Thirty-three normal volunteers were given three types of rice containing 0, 14 to 17, or 23 to 25% of carbohydrate in the form of amylose. The glucose and insulin responses were measured over a period of 180 min. Serum glucose response to high amylose rice was significantly lower at 30 min, and dropped more gradually by 180 min than with 0% amylose rice. In addition, the high amylose rice produced significantly lower insulin levels at 30 and 60 min, as well as lower integrated secretion over the 3-h test. Thus, our results suggest the presence of a factor in high-amylose rice which delays digestion and/or absorption of carbohydrate. Since fiber content and surface area of the test rices were identical, other factors must underlie these observed differences. These include differential enzymatic hydrolysis of amylose and amylopectin and the presence of lipid-starch complexes in the amylose-containing rice.     

The interaction between tea polyphenols and rice starch during gelatinization

The interaction between tea polyphenols (TPLs) and rice starch (RS) during gelatinization has been studied. In the RVA analysis, TPLs-fortified RS exhibited no clearly defined peak viscosity and hot paste viscosity. After excluding other factors, irregular viscosity changes were attributed to the strong interactions between RS and TPLs during pasting/gelatinization. Subsequently, the coupling constants of samples A (the gelatinized sample of the blend of 16% TPLs and RS) and B (the blend of 16% TPLs and gelatinized RS sample) in (1)H-NMR measurements were found to be the difference. Sample A had two coupling constants, (26h)J(HH)?=?82.08, 100.77?Hz and (6h)J(HH)?=?35.57?Hz, whereas Sample B had one larger coupling constant, (9h)J(HH)?=?140.24?Hz. This implied that these two samples differed in H-H interaction and interaction strength of sample A may be stronger than that of sample B. More important is, sample A had clearly broadened O-H stretching and frequency red-shifts of C-O-H bending as compared with sample B in quantitative FT-IR analysis. The overall results indicate that TPLs and RS can have hydrogen bonding interaction during gelatinization.     

Food physical factors have different metabolic effects in nondiabetics and diabetics

Physical properties of food may account for differences in glycemic and other metabolic responses to food with similar amounts of carbohydrate, fat and protein. Blending of cooked beans made no difference to plasma glucose, insulin, or GIP (gastric inhibitory polypeptide) responses in nondiabetics, NIDD (noninsulin-dependent diabetics), and IDD (insulin-dependent diabetics). The cooked blended beans gave a greater plasma glucose response and a lesser hormonal response than a cooked flummery (containing cornstarch, protein and fat) in nondiabetics. In NIDD and IDD, however, the reverse applied for plasma glucose. In nondiabetics, cooked flummery gave a lesser glycemic response at some time points than uncooked flummery. In NIDD the opposite occurred. Cooking led to no significant change in insulin response in nondiabetics, but to a lesser insulin response in NIDD. The effect of some physical properties of food on diabetic control cannot be inferred from findings in nondiabetics.     

Retrospective analysis of the impact of a low glycaemic index diet on hospital stay following coronary artery bypass grafting: a hypothesis

OBJECTIVE: Glucose tolerance and insulin resistance influence medical outcome in subjects with coronary artery disease, these metabolic parameters also influence general perioperative surgical outcome. We hypothesize that glucose tolerance and insulin resistance can be favourably modified by reducing the glycaemic index of the diet. DESIGN: The present study is a retrospective analysis of a low and high glycaemic index diet on glucose tolerance, insulin resistance and perioperative outcome, as assessed by the length of hospital stay following coronary artery bypass surgery. Thirty-five adults awaiting bypass surgery were randomized, for the 4 weeks prior to surgery, to either a low glycaemic index diet (17 subjects) or high glycaemic index diet (18 subjects). Glucose and insulin responses during a 75 g oral glucose tolerance test were assessed before and after dietary intervention and insulin-mediated glucose uptake was assessed in isolated adipocytes obtained at surgery. RESULTS: The patients who consumed a low glycaemic diet had improved glucose tolerance and significantly greater in vitro adipocyte insulin sensitivity at the time of surgery compared with the high glycaemic diet group (78.87 +/- 10.64% versus 41.11 +/- 7%, respectively). The total length of stay in the patients on the low glycaemic diet was less than patients consuming the high glycaemic diet (7.06 +/- 0.38 days versus 9.53 +/- 1.44 days, P < 0.5). CONCLUSION: This study provides further support that carbohydrate and fat metabolism influence cardiac outcome and provides new evidence that dietary modification prior to coronary artery bypass surgery can shorten hospital stay.     

The Glycaemic and Insulinaemic Response of Pasta in Chinese and Indians Compared to Asian Carbohydrate Staples: Taking Spaghetti Back to Asia

In this study, we compared the metabolic properties of the Asian staples rice and noodles, which are typically high in glycaemic index (GI), to two types of spaghetti. It is hypothesised that pasta can be a healthy replacement, particularly amongst the Asian population. Thirty Chinese and Indian subjects (17 men, 13 women; BMI: 18.5–25 kg/m²) participated in this randomised crossover trial. On seven occasions, they consumed a glucose reference drink (3 times), white rice, wheat-based mee pok noodles, semolina spaghetti and wholegrain spaghetti. Blood samples were taken to measure glucose and insulin response over a period of 3 h. The current evaluation showed that semolina spaghetti and wholegrain spaghetti can be classified as low GI products, with a GI of 53 and 54, respectively, significantly lower than wheat based mee pok noodles (74) and rice (80) (p < 0.005). In addition, both spaghettis had a lower insulin response compared to rice (p < 0.05). Furthermore, there was no difference in glucose or insulin response between semolina and wholegrain spaghetti. After controlling for gender, ethnicity, fat and fat free mass (kg), the glucose and insulin results did not change. In conclusion, wheat-based pasta can be helpful to modify the carbohydrate-rich Asian diet. Notably, there was no effect of gender, ethnicity and body composition on the glycaemic and insulinaemic response. We speculate that the starch-protein structure as a result of the spaghetti production process is a major driver of its favourable metabolic properties.     

Effect of processing on nutritionally important starch fractions in rice varieties

In the present study the effect of processing on starch fractions (rapidly digestible starch (RDS), slowly digestible starch (SDS) and resistant starch) were measured, using controlled enzymic hydrolysis with pancreatin and amyloglucidase, in six rice varieties; namely, BT rice, Gauri rice, Sona masoori, parboiled rice, Salem parboiled rice, and steamed rice. The processes studied were pressure cooking, boiling, steaming and straining. Rapidly available glucose (RAG) was also measured to derive a Starch Digestion Index (SDI). Cooking of rice by different methods decreased the amylose content. The degree of gelatinization ranged from 56 to 95, with pressure cooking resulting in the maximum degree. The starch fractions varied depending on the cooking method. Significant inverse correlations were seen between RDS and SDS (r = 0.40, P < 0.05), and between amylose and SDI (r = 0.60, P < 0.01). RAG and RDS related positively (r = 0.90, P < 0.01). The SDI of rice varieties cooked by the boiling and straining method were significantly higher (P < 0.05). The results emphasize that cooking methods influence the nutritionally important starch fractions in rice varieties.     

Glycemic index of processed wheat products

Our aim was to determine the in vivo glycemic and insulin responses and in vitro starch digestibility of seven processed wheat products (shortbread biscuits, custard, quick-cooking wheat, wholemeal bread, water biscuits, puffed wheat, and puffed crispbread). The degree of starch gelatinization in the foods was measured. Fifty-gram carbohydrate portions of the foods were fed to eight volunteers after an overnight fast. The calculated glycemic indices (GI) (mean +/- SEM) ranged from 43 +/- 10 for custard to 81 +/- 9 for puffed crispbread. Insulin responses paralleled the glycemic responses. The GI correlated positively with the percentage of starch digested in vitro (p less than 0.05). The degree of starch gelatinization ranged from 0.4 to 60% and correlated positively with the percentage starch digested in vitro (p less than 0.05). Differences in the glycemic and insulin responses to wheat products may be explained in part by the extent of processing and the degree of gelatinization achieved.     

Glycaemic index of parboiled rice depends on the severity of processing: study in type 2 diabetic subjects

OBJECTIVE: To study the influence of parboiling and the severity of the process on glycaemic and insulinaemic responses to rice in type 2 diabetes. Moreover, to examine changes in starch structure related to parboiling, which may affect the metabolic responses and digestibility. DESIGN: Nine type 2 diabetic subjects ingested four test meals: white bread (WB) and three meals of cooked polished rice of the same variety being non-parboiled (NP), mildly traditionally parboiled (TP) and severely pressure parboiled (PP). The participants ingested the test meals (50 g available carbohydrates) on separate occasions after an overnight fast. SETTING: Outpatient clinic, Dept. Endocrinology and Metabolism, Aarhus University Hospital, Denmark. RESULTS: All three rice samples elicited lower postprandial plasma glucose response (NP: 335+/-43; TP: 274+/-53; PP: 231+/-37 mmol/1*180 min.; means+/-s.e.m.) than white bread (626+/-80; P<0.001), within rice samples PP tended to be lower than NP (P=0.07). The glycaemic indices were: NP: 55+/-5, TP: 46+/-8 and PP: 39+/-6, and lower for PP than NP (P<0.05). The insulin responses were similar for the three rice meals, which were all lower than that to white bread (P<0.001). Differential scanning calorimetry showed the presence of amylose-lipid complexes in all rice samples and of retrograded amylopectin in PP. Amylose retrogradation was not detected in any of the rice samples. CONCLUSIONS: All rice test meals were low-glycaemic in type 2 diabetic subjects. There was no effect of TP on glycaemic index, whereas PP reduced the glycaemic index by almost 30% compared to NP. Sponsorship: The Royal Veterinary and Agricultural University, Aarhus University Hospital, Danish International Development Assistance (DANIDA), Ministry of Foreign Affairs and the 'Konsul Johannes Fogh-Nielsens og Fru Ella Fogh-Nielsens Legat' foundation.     

不同米饭对餐后血糖和饱腹感反应的影响

目的研究不同米饭样品的餐后血糖及饱腹感反应。方法 10名空腹健康志愿者食用含碳水化合物50 g的不同米饭样品:籼米饭(IR),黑籼米饭(BI),籼糯米饭(WL)和冷籼糯米饭(RW)。测餐后120 min血糖水平和血浆中胰岛素水平,同时记录180 min内的饱腹感及第二餐摄入的能量,计算血糖生成指数(GI)与胰岛素生成指数(II),以及在餐后1 h,2 h和3 h时各样品的饱腹感指数(SI)。结果无论WL还是RW食用后的GI均高于IR和BI。BI的II和SI最高。第二餐能量摄入最低。II分别与GI和SI具有一定的相关性,而GI和SI之间的相关性不大。结论籼糯米饭经过冷藏以后并不能降低血糖反应,两者均不适合糖尿病人作为主食BI适合需要控制体重和控制血糖者食用。结果提示,相比于GI,II与SI之间的联系可能更密切。     

An overview of the role of rice in the UK diet

Rice is a staple food for over half of the world's population. Eighty percent of the British population buy rice, predominantly white rice, with the average person consuming approximately 5.6 kg per year. Rice consumption in the UK is expected to increase slightly, as a result of the growing ethnic population and food diversification. Starchy foods such as rice, potatoes, bread and cereals are our main source of carbohydrate and play an important role in a healthy diet. As well as providing energy, rice contains other essential nutrients such as thiamine, riboflavin, niacin, vitamin E, zinc, potassium, iron and fibre. On cooking, rice swells to at least three times its original weight and therefore benefits from a low‐energy density compared to other starchy carbohydrate foods (e.g. bread), as well as a low‐sodium content (unless salt is added to rice products). It has a low allergenicity and is relatively easy to digest, making it a useful food for early weaning or during convalescence. The Department of Health encourage the selection of wholegrain versions of starchy carbohydrate foods as these are higher in fibre. Brown rice also has a higher proportion of important bioactive phytochemicals such as hemicelluloses and lignans with antioxidant and anti‐inflammatory properties that may benefit health. Despite the common perception that starchy carbohydrate foods are ‘fattening’, diets containing rice have been shown to achieve weight loss in obese subjects, although greater weight reduction has been shown with mixed rice compared with white rice. Although the reported glycaemic index (GI) of different rice varieties is inconsistent, most types of rice are classified as low or medium ‘GI’ foods but this is influenced by cooking time, the degree of gelatinisation and rice type. While there are numerous studies that have examined the link between high‐carbohydrate intakes and risk of chronic diseases such as obesity, type 2 diabetes and cardiovascular disease, relatively few have investigated the role of rice specifically, particularly in western populations. In Asian populations in whom rice is a staple food, higher white rice consumption has been associated with elevated risk of diabetes and metabolic syndrome. Some prospective cohort studies in the US have linked regular consumption of white rice with higher risk of type 2 diabetes, whereas brown rice intake was associated with lower risk. These studies were however observational in nature and so cannot determine a ‘cause and effect’ relationship, whilst their findings may be subject to residual confounding. Future studies should consider potential differences of white rice varieties, which vary in amylose content, as well as the effect of processing methods.     

Influence of Energy Balance and Glycemic Index on Metabolic Endotoxemia in Healthy Men

Objective: Overfeeding with a high-fat and/or high-carbohydrate (CHO) diet is known to increase plasma concentrations of endotoxin (lipopolysaccharide [LPS]) that may lead to metabolic disturbances like insulin resistance. The impact of CHO quality (i.e., the glycemic index [GI]) independent of fat intake on metabolic endotoxemia remains unclear. In the present study, the effects of changes in energy balance and GI on plasma endotoxin were studied.

Methods: Fifteen healthy young men overconsumed diets containing 65% CHO and 20% fat for 1 week (OF; +50% of energy requirement) followed by 3 weeks of caloric restriction (CR; ?50% of energy requirement) and were then randomized to 2 weeks hypercaloric refeeding (RF, +50% of energy requirement) with either a low- or high-GI (40 vs 74) diet.

Results: During OF, subjects gained 1.9 ± 0.7 kg body weight (+0.6 ± 0.8% fat mass) followed by a weight loss of 6.1 ± 0.8 kg (?2.0 ± 0.6% fat mass) and weight regain of 4.0 ± 0.6 kg (0.9 ± 0.8% fat mass). Fasting insulin and homeostasis model assessment–insulin resistance (HOMA_IR) increased with OF and RF and decreased with CR, Matsuda_ISI decreased by 37% after RF (all p < 0.05). Endotoxin significantly increased by 30.8% with OF and by 24.7% with RF (both p < 0.05), whereas CR normalized endotoxin levels. No difference in endotoxin levels was observed between refeeding a hypercaloric high- or low-GI diet. Changes in endotoxin levels with RF were not related to changes in insulin sensitivity.

Conclusion: A hypercaloric diet (OF and RF) increased plasma endotoxin irrespective of GI, whereas a negative energy balance did not reduce endotoxemia. Impaired insulin sensitivity with hypercaloric refeeding on a high-GI diet was not explained by metabolic endotoxemia.     

Blood glucose lowering effects of brown rice in normal and diabetic subjects

Carbohydrate foods, which produce low glycemic responses, have been shown to be beneficial in the dietary management of chronic diseases such as diabetes and hyperlipidemia. This study determined the starch digestion rate in vitro and, in a randomised crossover design, the postprandial blood glucose response of 10 healthy and nine type 2 diabetic volunteers to brown rice compared to milled rice from the same batch and variety. The total sugar released in vitro was 23.7% lower in brown rice than in milled rice. In healthy volunteers, the glycemic area and glycemic index were, respectively, 19.8% and 12.1% lower (p < 0.05) in brown rice than milled rice, while in diabetics, the respective values were 35.2% and 35.6% lower. The effect was partly due to the higher amounts of phytic acid, polyphenols, dietary fiber and oil in brown compared to milled rice and the difference in some physicochemical properties of the rice samples such as minimum cooking time and degree of gelatinisation. In conclusion, brown rice is a more health beneficial food for diabetics and hyperglycemic individuals than milled rice.