Dietary amylose-amylopectin starch content affects glucose and lipid metabolism in adipocytes of normal and diabetic rats

Biosynthesis of artificial starch and microbial protein from agricultural residue

Growing populations and climate change pose great challenges to food security. Humankind is confronting a serious question: how will we feed the world in the near future? This study presents an out-of-the-box solution involving the highly efficient biosynthesis of artificial starch and microbial proteins from available and abundant agricultural residue as new feed and food sources. A one-pot biotransformation using an in vitro coenzyme-free synthetic enzymatic pathway and baker's yeast can simultaneously convert dilute sulfuric acid-pretreated corn stover to artificial starch and microbial protein under aerobic conditions. The β-glucosidase-free commercial cellulase mixture plus an ex vivo two-enzyme complex containing cellobiose phosphorylase and potato α-glucan phosphorylase displayed on the surface of Saccharomyces cerevisiae, showed better cellulose hydrolysis rates than a commercial β-glucosidase-rich cellulase mixture. This is because the channeling of the hydrolytic product from the solid cellulosic feedstock to the yeast mitigated the inhibition of the cellulase cocktail. Animal tests have shown that the digestion of artificial amylose results in slow and relatively small changes in blood sugar levels, suggesting that it could be a new health food component that prevents obesity and diabetes. A combination of the utilization of available agricultural residue and the biosynthesis of starch and microbial protein from non-food biomass could address the looming food crisis in the food-energy-water nexus.

Continuous glucose monitoring reveals similar glycemic variability in individuals with obesity despite increased HOMA-IR

Background/aims

Continuous glucose monitoring is a well-tolerated and versatile tool for management of diabetes and metabolic disease. While its use appears to be feasible to monitor glycemic profiles in diabetics, there is a paucity of data in individuals with obesity and normal glucose tolerance. The aim of this study is to investigate glucose fluctuations and insulin resistance patterns in normoglycemic participants with obesity vs. without obesity and contextualize these results against leading models for obesity.

Materials and methods

We designed a prospective, observational pilot study of two cohorts including 14 normoglycemic participants with obesity and 14 normoglycemic participants without obesity. Participants were monitored with continuous glucose monitoring (CGM) for five consecutive days. Insulin resistance levels were measured and glucometric data were extracted from CGM for all participants.

Results

Fasting serum insulin and homeostasis model assessment of insulin resistance (HOMA-IR) were significantly higher in the group with obesity (P < 0.05). While the group with obesity had a higher mean blood glucose (MBG), mean amplitude of glycemic excursions (MAGE), and continuous overall glycemic action-1 h (CONGA-1), these differences were not significant. On univariate linear regression, insulin resistance (HOMA-IR) was associated with body mass index (BMI), waist circumference (WC), cohort with obesity, cohort consuming a high glycemic diet, hemoglobin A1c (HbA1c), and fasting insulin levels. WC and fasting insulin levels remained predictors of HOMA-IR in our multivariable model.

Conclusion

While there is much excitement surrounding the use of commercial CGM products in obesity management, our results suggest that fasting insulin and HOMA-IR values may be more clinically useful than CGM data alone.

A comparison between whole mung bean and decorticated mung bean: beneficial effects on the regulation of serum glucose and lipid disorders and the gut microbiota in high-fat diet and streptozotocin-induced prediabetic mice

The aim of this study is to investigate the beneficial effects of whole mung bean (WMB) and decorticated mung bean (DMB) on the regulation of serum glucose and lipid disorders in high-fat diet (HFD) and streptozotocin (STZ)-induced prediabetic mice, and to further explore their gut microbiota modulatory effects. In the present study, the ability of mung bean-based diets to combat prediabetes-related metabolic disorders was determined by assessing the changes in the physiological, biochemical, and histological parameters, and the gut microbiota composition of prediabetic mice. The supplementation of both WMB and DMB can effectively alleviate HFD and STZ-induced impaired glucose tolerance (P < 0.05), which was accompanied by improvements in pancreatic β-cell damage and hepatic steatosis. However, only WMB supplementation significantly decreased the fasting blood glucose and fasting serum insulin levels by sensitizing insulin action (P < 0.05), and reduced the serum lipid profiles and glycosylated serum protein levels (P < 0.05). Furthermore, high-throughput pyrosequencing of the 16S rRNA gene revealed that WMB and DMB supplementation could prevent HFD and STZ-induced gut microbiota dysbiosis, especially for the enrichment of some benign bacteria, such as Bifidobacterium and Akkermansia, and the reduction of some harmful bacteria (Staphylococcus and Enterococcus). Overall, although decortication processing had an impact on the beneficial effects of mung bean, it did not cause the loss of all health benefits.

Effects of the amount and type of carbohydrates used in type 2 diabetes diets in animal models: A systematic review

Type 2 diabetes mellitus (T2DM) is among the most prevalent diseases in the world, affecting over 420 million people. The disease is marked by a poor metabolic effect of insulin leading to chronic hyperglycaemia, which can result in microvascular complications. It is widely known that postprandial glycaemia is reliant on the total carbohydrate content of a meal. However, the importance of the amount and the source of these carbohydrates remains controversial due to mechanisms other than insulin secretion. Oxidative stress, inflammation, pyruvate production and the quality of the intestinal microbiota, resulting in plasma lipopolysaccharides and short-chain fatty acids production, play an important role in blood sugar control and consequently in type 2 diabetes. Thus, we systematically reviewed the preclinical evidences on the impact of the amount and type of carbohydrate found in different diets and its influence on blood glucose levels in diabetic animals. We used a comprehensive and structured search in biomedical databases Medline (PubMed), Scopus and Web of Science, recovering and analyzing 27 original studies. Results showed that sucrose-rich diets deteriorated diabetic condition in animal models regardless of the total dietary carbohydrate content. On the other hand, fiber, particularly resistant starch, improved blood glucose parameters through direct and indirect mechanisms, such as delayed gastric emptying and improved gut microbiota. All studies used rodents as animal models and male animals were preferred over females. Improvements in T2DM parameters in animal models were more closely related to the type of dietary carbohydrate than to its content on a diet, i. e., resistant starch seems to be the most beneficial source for maintaining normoglycemia. Results show that current literature is at high risk of bias due to neglecting experimental methods.

A Lowly Digestible-Starch Diet after Weaning Enhances Exogenous Glucose Oxidation Rate in Female, but Not in Male, Mice

Starches of low digestibility are associated with improved glucose metabolism. We hypothesise that a lowly digestible-starch diet (LDD) versus a highly digestible-starch diet (HDD) improves the capacity to oxidise starch, and that this is sex-dependent. Mice were fed a LDD or a HDD for 3 weeks directly after weaning. Body weight (BW), body composition (BC), and digestible energy intake (dEI) were determined weekly. At the end of the intervention period, whole-body energy expenditure (EE), respiratory exchange ratio (RER), hydrogen production, and the oxidation of an oral ¹³C-labelled starch bolus were measured by extended indirect calorimetry. Pancreatic amylase activity and total ¹³C hepatic enrichment were determined in females immediately before and 4 h after administration of the starch bolus. For both sexes, BW, BC, and basal EE and RER were not affected by the type of starch, but dEI and hydrogen production were increased by the LDD. Only in females, total carbohydrate oxidation and starch-derived glucose oxidation in response to the starch bolus were higher in LDD versus HDD mice; this was not accompanied by differences in amylase activity or hepatic partitioning of the ¹³C label. These results show that starch digestibility impacts glucose metabolism differently in females versus males.

Mung Bean (Vigna radiata L.): Bioactive Polyphenols, Polysaccharides, Peptides, and Health Benefits

Mung bean (Vigna radiata L.) is an important pulse consumed all over the world, especially in Asian countries, and has a long history of usage as traditional medicine. It has been known to be an excellent source of protein, dietary fiber, minerals, vitamins, and significant amounts of bioactive compounds, including polyphenols, polysaccharides, and peptides, therefore, becoming a popular functional food in promoting good health. The mung bean has been documented to ameliorate hyperglycemia, hyperlipemia, and hypertension, and prevent cancer and melanogenesis, as well as possess hepatoprotective and immunomodulatory activities. These health benefits derive primarily from the concentration and properties of those active compounds present in the mung bean. Vitexin and isovitexin are identified as the major polyphenols, and peptides containing hydrophobic amino acid residues with small molecular weight show higher bioactivity in the mung bean. Considering the recent surge in interest in the use of grain legumes, we hope this review will provide a blueprint to better utilize the mung bean in food products to improve human nutrition and further encourage advancement in this field.

Low-Carb and Ketogenic Diets in Type 1 and Type 2 Diabetes

Low-carb and ketogenic diets are popular among clinicians and patients, but the appropriateness of reducing carbohydrates intake in obese patients and in patients with diabetes is still debated. Studies in the literature are indeed controversial, possibly because these diets are generally poorly defined; this, together with the intrinsic complexity of dietary interventions, makes it difficult to compare results from different studies. Despite the evidence that reducing carbohydrates intake lowers body weight and, in patients with type 2 diabetes, improves glucose control, few data are available about sustainability, safety and efficacy in the long-term. In this review we explored the possible role of low-carb and ketogenic diets in the pathogenesis and management of type 2 diabetes and obesity. Furthermore, we also reviewed evidence of carbohydrates restriction in both pathogenesis of type 1 diabetes, through gut microbiota modification, and treatment of type 1 diabetes, addressing the legitimate concerns about the use of such diets in patients who are ketosis-prone and often have not completed their growth.

The Carbohydrate-Insulin Model of Obesity: Beyond "Calories In, Calories Out"

Despite intensive research, the causes of the obesity epidemic remain incompletely understood and conventional calorie-restricted diets continue to lack long-term efficacy. According to the carbohydrate-insulin model (CIM) of obesity, recent increases in the consumption of processed, high-glycemic-load carbohydrates produce hormonal changes that promote calorie deposition in adipose tissue, exacerbate hunger, and lower energy expenditure. Basic and genetic research provides mechanistic evidence in support of the CIM. In animals, dietary composition has been clearly demonstrated to affect metabolism and body composition, independently of calorie intake, consistent with CIM predictions. Meta-analyses of behavioral trials report greater weight loss with reduced-glycemic load vs low-fat diets, though these studies characteristically suffer from poor long-term compliance. Feeding studies have lacked the rigor and duration to test the CIM, but the longest such studies tend to show metabolic advantages for low-glycemic load vs low-fat diets. Beyond the type and amount of carbohydrate consumed, the CIM provides a conceptual framework for understanding how many dietary and nondietary exposures might alter hormones, metabolism, and adipocyte biology in ways that could predispose to obesity. Pending definitive studies, the principles of a low-glycemic load diet offer a practical alternative to the conventional focus on dietary fat and calorie restriction.

Predisposition to insulin resistance and obesity due to staple consumption of rice: Amylose content versus germination status

Type 2 diabetes is a metabolic disorder with established, well-defined precursors. Obesity and insulin resistance are amongst most important factors in predisposition to diabetes. Rice is a staple for about half the global population and its consumption has been strongly linked with diabetogenesis. We assert that tackling the prevalence of predisposing factors by modifying certain rice cultivars could reduce the global burden of obesity and insulin resistance, and by extension type 2 diabetes. Several rice cultivars with various properties were fed to nulliparous rats (five weeks old at the start of the experiment) for 90 days. They were then returned to a diet of standard pellets and mated with males raised on a standard diet. The resulting pups and dams were investigated for obesity and insulin resistance markers. We found that germination did more to reduce predisposition to obesity and insulin resistance than high amylose content. The combined reducing effect of germination and high amylose content on predisposition to obesity and insulin resistance was greater than the sum of their independent effects. Polished (white) rice with a low amylose content predisposed dams on a high-fat diet to markers of insulin resistance and obesity and this predisposition was inherited (in biochemical terms) by their F1 offspring. Overall, the results suggest that harnessing the beneficial properties of germination and amylose in rice would reduce the burden of obesity and insulin resistance, which are known to be key risk factors for development of type 2 diabetes.

Treatment of reactive hypoglycemia with the macrobiotic Ma-pi 2 diet as assessed by continuous glucose monitoring: The MAHYP randomized crossover trial

BACKGROUND AND AIMS

Nutritional therapy is recommended for management of reactive hypoglycemia (RH), a condition characterized by hypoglycemia that occurs within four hours after a meal. The macrobiotic Ma-Pi 2 diet improves glycemic control in subjects with type 2 diabetes. We explored the effect of this diet on outcomes in non-diabetic individuals with RH.

MATERIALS AND METHODS

Twelve subjects with RH were randomized to the Ma-Pi 2 diet for three days and a control diet for three days in a randomized crossover design. Subjects received snacks on two days out of each three-day period only, and were monitored using continuous glucose monitoring. The 24-h period was divided into daytime (08:00-22:30h [subdivided into 'daytime without snacks' and 'daytime with snacks']) and night-time (22:31-07:59h). The effects of the two diets on the number of RH events (blood glucose <70mg/dL [3.9mmol/L]) and the percentage distribution of glucose readings within each of 16 glycemic intervals from <40mg/dL (2.2mmol/L) to >180mg/dL (4.4mmol/L) were determined.

RESULTS

There were significantly fewer RH events on the Ma-Pi 2 diet than the control diet during daytime without snacks (-2.5 events; 95% CI: -7.5, 0.0; P=0.022) and daytime with snacks (-4.25 events; 95% CI: -7.5; -2.0; P=0.013) but no difference at night. The percentage of glucose readings in the interval 71-80mg/dL (3.9-4.4mmol/L) was significantly higher on the control diet during daytime with and without snacks (P=0.03 for both), while the percentage of glucose readings in the interval 91-100mg/dL (5.1-5.6mmol/L) was significantly higher on the Ma-Pi 2 diet during daytime without snacks (P=0.02).

CONCLUSIONS

The macrobiotic Ma-Pi 2 diet reduced blood glucose excursions during the day, thereby facilitating glycemic control in subjects with RH. The Ma-Pi 2 diet represents an effective nutritional tool for management of RH.

Antioxidant and Antihyperglycemic Properties of Three Banana Cultivars (Musa spp.)

Background. This study sought to investigate the antioxidant and antihyperglycemic properties of Musa sapientum (Latundan banana) (MSL), Musa acuminata (Cavendish banana) (MAC), and Musa acuminate (Red Dacca) (MAR). Materials and Methods. The sugar, starch, amylose, and amylopectin contents and glycemic index (GI) of the three banana cultivars were determined. Furthermore, total phenol and vitamin C contents and α-amylase and α-glucosidase inhibitory effects of banana samples were also determined. Results. MAC and MAR had the highest starch, amylose, and amylopectin contents and estimated glycemic index (eGI) with no significant different while MSL had the lowest. Furthermore, MAR (1.07 mg GAE/g) had a higher total phenol content than MAC (0.94 mg GAE/g) and MSL (0.96 mg GAE/g), while there was no significant difference in the vitamin C content. Furthermore, MAR had the highest α-amylase (IC₅₀ = 3.95 mg/mL) inhibitory activity while MAC had the least (IC₅₀ = 4.27 mg/mL). Moreover, MAC and MAR inhibited glucosidase activity better than MSL (IC₅₀ 3.47 mg/mL). Conclusion. The low sugar, GI, amylose, and amylopectin contents of the three banana cultivars as well as their α-amylase and α-glucosidase inhibitory activities could be possible mechanisms and justification for their recommendation in the management of type-2 diabetes.

Starch utilisation in chicken-meat production: the foremost influential factors

Starch is the chief dietary energy source for chicken-meat production, the majority of which is derived from the grain basis of diets for broiler chickens. The utilisation of starch from maize is of a high order in terms of ileal starch digestibility coefficients but this is not necessarily the case with wheat or sorghum. This may stem from the fact that maize essentially lacks the soluble non-starch polysaccharides in wheat and ‘non-tannin’ phenolic compounds found in sorghum. Numerous factors may influence starch digestibility with emphasis placed on starch–protein interactions as starch granules are located in the prolamin protein matrixes of grain endosperm. This close proximity facilitates any physical and chemical interactions and in this connection particular attention has been paid to kafirin, the dominant protein fraction in sorghum. Nevertheless, despite their apparent importance, the precise nature of starch–protein interactions has not been well defined. Exogenous phytases are routinely included in broiler diets primarily to liberate phytate-bound phosphorus; however, phytate may impede starch digestion and may retard glucose absorption. Additional feed additives, including non-starch polysaccharide-degrading enzymes, other exogenous enzymes and reducing agents may have the capacity to influence starch utilisation. Nevertheless, ileal and total tract starch digestibility coefficients are static parameters and overlook the digestive dynamics of starch, which is inappropriate given the possibility that slowly digestible starch enhances energy utilisation and feed conversion efficiency. However, if the slowly digestible starch concept is valid, the underlying mechanisms have not been fully elucidated. Consideration is given to the suggestion that slowly digestible starch ameliorates the catabolism of amino acids to provide energy to the gut mucosa by increasing the provision of glucose to posterior small intestinal segments. There is the prospect that whole grain feeding provides slowly digestible starch in addition to generating heavier relative gizzard weights. The digestive dynamics of starch and protein are inter-related and the digestion of starch and absorption of glucose should not be considered in isolation from protein digestion and amino acid absorption in the quest to improve the performance of broiler chickens. The foremost factor influencing starch utilisation in chicken-meat production may be the interaction between starch and protein digestive dynamics.

The Intra- or Extracellular Redox State Was Not Affected by a High vs. Low Glycemic Response Diet in Mice

A low glycemic response (LGR) vs. high glycemic response (HGR) diet helps curtail the development of obesity and diabetes, though the mechanisms are unknown. We hypothesized that consumption of a HGR vs. a LGR diet would lead to a more oxidized circulating redox state and predicted that a HGR diet would increase fat accumulation, reduce insulin sensitivity, and impair metabolic acclimation to a high fat diet in a mouse model. Hence, male C57BL/6 mice consumed a HGR or LGR diet for 16 weeks and a subset of the mice subsequently consumed a high fat diet for 4 weeks. We found that body mass increased at a faster rate for those consuming the HGR diet. Percent body fat was greater and percent lean mass was lesser in the HGR group starting at 12 weeks. However, the groups did not differ in terms of glucose tolerance at week 14 and metabolic parameters (respiratory exchange ratio, heat production, activity) at weeks 4 or 15. Moreover, mice on either diet did not show differences in metabolic acclimation to the high fat leg of the study. At the termination of the study, the groups did not differ in terms of redox pairs (lactate/pyruvate and β-hydroxybutyrate/acetoacetate) or thioredoxin reductase activity in blood. Also, total and oxidized glutathione levels and lipid peroxidation were similar in blood and liver. Correlations between baseline measures, longitudinal parameters, environmental conditions, and terminal metrics revealed that individual mice have innate propensities to metabolic regulation that may be difficult to perturb with diet alone; for example, starting mass correlated negatively with energy expenditure 4 weeks into the study and total hepatic glutathione at the end of the study. In conclusion, these data suggest that the mechanism by which HGR carbohydrates contributes to obesity is not via prolonged oxidation of the circulating redox state.

Effects of dietary amylose/amylopectin ratio on growth performance, feed utilization, digestive enzymes, and postprandial metabolic responses in juvenile obscure puffer Takifugu obscurus

The effect of dietary amylose/amylopectin (AM/AP) ratio on growth, feed utilization, digestive enzyme activities, plasma parameters, and postprandial blood glucose responses was evaluated in juvenile obscure puffer, Takifugu obscurus. Five isonitrogenous (430 g kg(-1) crude protein) and isolipidic (90 g kg(-1) crude lipid) diets containing an equal starch level (250 g kg(-1) starch) with different AM/AP ratio diets of 0/25, 3/22, 6/19, 9/16 and 12/13 were formulated. Each experimental diet was fed to triplicate groups (25 fish per tank), twice daily during a period of 60 days. After the growth trial, a postprandial blood response test was carried out. Fish fed diet 6/19 showed best growth, feed efficiency and protein efficiency ratio. Hepatosomatic index, plasma total cholesterol concentration, liver glycogen and lipid content, and gluconokinase, pyruvate kinase and fructose-1,6-bisphosphatase activities were lower in fish fed highest AM/AP diet (12/13) than in fish fed the low-amylose diets. Activities of liver and intestinal trypsin in fish fed diet 3/22 and diet 6/19 were higher than in fish fed diet 9/16 and diet 12/13. Activities of liver and intestinal amylase and intestinal lipase, and starch digestibility were negatively correlated with dietary AM/AP ratio. Fish fed diet 3/22 and diet 6/19 showed higher plasma total amino acid concentration than fish fed the other diets, while plasma urea nitrogen concentration and activities of alanine aminotransferase and aspartate aminotransferase showed the opposite trend. Equal values were found for viscerosomatic index and condition factor, whole body and muscle composition, plasma high-density and low-density lipoprotein cholesterol concentrations, and activities of lipase and hexokinase and glucose-6-phosphatase in liver. Postprandial plasma glucose and triglyceride peak value of fish fed diet 12/13 were lower than in fish fed the low-amylose diets, and the peak time of plasma glucose was later than in fish fed the other diets. Plasma glucose and triglyceride concentrations showed a significant difference at 2 and 4 h after a meal and varied between dietary treatments. According to regression analysis of weight gain against dietary AM/AP ratio, the optimum dietary AM/AP ratio for maximum growth of obscure puffer was 0.25. The present result indicates that dietary AM/AP ratio could affect growth performance and feed utilization, some plasma parameters, digestive enzyme as well as hepatic glucose metabolic enzyme activities in juvenile obscure puffer.

Resistant starch and energy balance: impact on weight loss and maintenance

The obesity epidemic has prompted researchers to find effective weight-loss and maintenance tools. Weight loss and subsequent maintenance are reliant on energy balance--the net difference between energy intake and energy expenditure. Negative energy balance, lower intake than expenditure, results in weight loss whereas positive energy balance, greater intake than expenditure, results in weight gain. Resistant starch has many attributes, which could promote weight loss and/or maintenance including reduced postprandial insulinemia, increased release of gut satiety peptides, increased fat oxidation, lower fat storage in adipocytes, and preservation of lean body mass. Retention of lean body mass during weight loss or maintenance would prevent the decrease in basal metabolic rate and, therefore, the decrease in total energy expenditure, that occurs with weight loss. In addition, the fiber-like properties of resistant starch may increase the thermic effect of food, thereby increasing total energy expenditure. Due to its ability to increase fat oxidation and reduce fat storage in adipocytes, resistant starch has recently been promoted in the popular press as a "weight loss wonder food". This review focuses on data describing the effects of resistant starch on body weight, energy intake, energy expenditure, and body composition to determine if there is sufficient evidence to warrant these claims.

Growth, Feed Utilization and Blood Metabolic Responses to Different Amylose-amylopectin Ratio Fed Diets in Tilapia (Oreochromis niloticus)

A feeding trial was conducted in tilapia to determine the growth performance, nutrient digestibility, digestive enzymes, and postprandial blood metabolites in response to different dietary amylose-amylopectin ratios. Five isonitrogenous and isolipidic diets containing an equal starch level with different amylose-amylopectin ratios of 0.11 (diet 1), 0.24 (diet 2), 0.47 (diet 3), 0.76 (diet 4) and 0.98 (diet 5) were formulated using high-amylose corn starch (as the amylose source) and waxy rice (as the amylopectin source). Each diet was hand-fed to six tanks of 15 fish each, three times a day over a 6-wk period. After the growth trial, a postprandial blood metabolic test was carried out. Fish fed diet 2 exhibited the highest percent weight gain and feed efficiency and protein efficiency ratio, whereas fish fed with diet 5 showed the lowest growth and feed utilization among treatments. The digestibility for starch in fish fed diet 1 and 2 was higher than those in fish fed with other diets (p<0.05). The highest activities for protease, lipase and amylase were found in fish fed the diet 2, diet 1, and diet 1 respectively among dietary treatments, while the lowest values for these indexes were observed in fish fed the diet 3, diet 5 and diet 4, respectively. The liver glycogen concentrations in fish fed diets 4 and 5 were found higher than in fish fed other diets (p<0.05). The feeding rate, hepatosomatic index, condition factor, and plasma parmeters (glucose, triglyceride, total cholesterol, high-density lipoprotein cholesterol, and low-density lipoprotein cholesterol) did not differ across treatments. In terms of postprandial blood responses, peak blood glucose and triglycerides were lower after 3 or 6 h in the fish fed with diets 3-5 than in the fish fed diet 1, but delayed peak blood total amino acid time was observed in fish fed with the diets 1 or 2. The lowest peak values for each of the three blood metabolites were observed in fish fed diet 5. The results indicate that high-dietary amylose-amylopectin ratio could compromise growth, but help in reducing the blood glucose stress on fish caused by postprandial starch load.

Antidiabetic potential of commonly consumed legumes: a review

Over the last few decades, lifestyle changes have resulted in a drastic increase in the incidence of diabetes all over the world, especially in the developing countries. Oral hypoglycemic agents and insulin form the mainstay in controlling diabetes, but they have prominent side effects and fail to significantly alter the course of diabetic complications. Appropriate diet and exercise programs that form a part of lifestyle modifications have proven to be greatly effective in the management of this disease. Dietary therapy is showing a bright future in the prevention and treatment of diabetes. Legumes, owing to their high nutritive value, are increasingly being used in dietetic formulations in the treatment and prevention of diabetes on account of their antidiabetic potential. Given this background, this paper reviews the glucose- and lipid-lowering action possessed by various commonly consumed legumes through several animal and human studies. It is concluded that the various legumes not only have varying degrees of antidiabetic potential but are also beneficial in decreasing the risk factors for cardiovascular and renal disease.

Nutritional and health perspectives of beans (Phaseolus vulgaris L.): an overview

Beans, the variants of Phaseolus vulagris, are nutritionally and economically important food crop in each part of the world. Besides providing nutrients such as multifaceted carbohydrates, elevated proteins, dietary fiber, minerals, and vitamins, these also contain rich variety of polyphenolic compounds with prospective health benefits. This review mainly focuses the important nutritional aspects of beans as well as their contribution in decreasing the risks of chronically degenerative diseases.

Evaluation of the antioxidant and melanogenesis inhibitory properties of pracparatum mungo (lu-do huang)

Pracparatum mungo (Lu-Do Huang) is a traditional Chinese functional medicine made from the natural fermentation of mung bean (Lǜ Dòu) mixed with other Chinese medicines. It has been recognized as having liver protecting and detoxifying effects. As mung beans have been verified to possess anti-inflammatory, antioxidant, antipyretic, and whitening actions, the present research utilized the in vitro, ex vivo, and in vivo experimental models to investigate the antioxidant and melanin inhibiting effects of P. mungo on the skin. The in vitro experiment revealed that P. mungo methanol extract (PMME) and P. mungo ethanol extract (PMEE) possess the capacity to clear α,α-diphenyl-2-picrylhydrazyl (DPPH) radicals and inhibit tyrosinase activity. The ex vivo experiment indicated that PMEE can promote the growth of MDCK cells and increase the enzymatic activities of superoxide dismutase (SOD) and catalase in MDCK cells. On the other hand, PMME and PMEE can suppress the proliferation of A375 cells, and PMEE can reduce the enzymatic activities of SOD and catalase in A375 cells. The in vivo results showed that P. mungo can enhance the enzymatic performance of SOD, Catalase, and glutathione peroxidase (GPx) in the liver. The results also showed that P. mungo has antioxidant characteristics and can inhibit tyrosinase activity, thereby promoting the growth of skin tissues and suppressing the proliferation of A375 cells, and thus enhancing the effects that the antioxidant enzymatic performance has on the liver. These results can be applied in the development of tyrosinase inhibitors or antioxidants used for the inhibition of melanin biosynthesis or for auto-oxidation in further industrial applications, particularly those relating to functional food or cosmetic compositions.

Pasta supplemented with isolated lupin protein fractions reduces body weight gain and food intake of rats and decreases plasma glucose concentration upon glucose overload trial

The supplementation of foods with biologically active seed proteins can be a powerful approach for controlling body weight gain and glycaemia, thus improving well being.

Resistant starch intake partly restores metabolic and inflammatory alterations in the liver of high-fat-diet-fed rats

Insulin resistance (IR) constitutes the most important feature of the metabolic syndrome, whose prevalence is highly associated to the consumption of Western diets. Resistant starch (RS) consumption has been shown to have beneficial metabolic effects, including improved insulin sensitivity, and glucose and lipid homeostasis. However, the mechanisms (especially at the molecular level) by which this takes place are still not completely known. In the present study, we aimed to evaluate the role of the liver in the ameliorated high-fat (HF)-induced IR status by RS. Thus, three groups of rats were fed either a control diet, or an HF diet containing or not RS. After 9 weeks of feeding, we evaluated the whole-body insulin sensitivity, and the hepatic glucose and lipid metabolism at the biochemical and molecular levels and the metabolome of the cecum content. We demonstrated for the first time that at least part of the beneficial effects of RS consumption in the context of an HF feeding can be driven by changes elicited at the hepatic level. The ability of the RS to correct the HF-induced dyslipidemia and the associated IR resulted from the return to the basal expression levels of transcription factors involved in lipogenesis (SREBP-1c), cholesterol metabolism (SREBP-2, LXRs) and fatty acid oxidation (PPARα). Moreover, the RS feeding was able to correct the HF-induced reduction in hepatic glucose phosphorylation and muscle glucose transport, improving glucose tolerance. Finally, as a whole, the improved hepatic metabolism seemed to be the result of an ameliorated inflammatory status.

Glycemic index differences of high-fat diets modulate primarily lipid metabolism in murine adipose tissue

A low vs. high glycemic index of a high-fat (HF) diet (LGI and HGI, respectively) significantly retarded adverse health effects in adult male C57BL/6J mice, as shown recently (Van Schothorst EM, Bunschoten A, Schrauwen P, Mensink RP, Keijer J. FASEB J 23: 1092–1101, 2009). The LGI diet enhanced whole body insulin sensitivity and repressed HF diet-induced body and white adipose tissue (WAT) weight gain, resulting in significantly reduced serum leptin and resistin levels and increased adiponectin levels. We questioned how WAT is modulated and characterized the molecular mechanisms underlying the glycemic index-mediated effects using whole genome microarrays. This showed that the LGI diet mainly exerts its beneficial effects via substrate metabolism, especially fatty acid metabolism. In addition, cell adhesion and cytoskeleton remodeling showed reduced expression, in line with lower WAT mass. An important transcription factor showing enhanced expression is PPAR-γ. Furthermore, serum levels of triglycerides, total cholesterol, and HDL- and LDL-cholesterol were all significantly reduced by LGI diet, and simultaneously muscle insulin sensitivity was significantly increased as analyzed by protein kinase B/Akt phosphorylation. Cumulatively, even though these mice were fed an HF diet, the LGI diet induced significantly favorable changes in metabolism in WAT. These effects suggest a partial overlap with pharmacological approaches by thiazolidinediones to treat insulin resistance and statins for hypercholesterolemia. It is therefore tempting to speculate that such a dietary approach might beneficially support pharmacological treatment of insulin resistance or hypercholesterolemia in humans.

Resistant starch and exercise independently attenuate weight regain on a high fat diet in a rat model of obesity

BACKGROUND

Long-term weight reduction remains elusive for many obese individuals. Resistant starch (RS) and exercise may be useful for weight maintenance. The effects of RS, with or without exercise, on weight regain was examined during relapse to obesity on a high carbohydrate, high fat (HC/HF) diet.

METHODS

Obesity-prone rats were fed ad libitum for 16 weeks then weight reduced on a low fat diet to induce a 17% body weight loss (weight reduced rats). Weight reduced rats were maintained on an energy-restricted low fat diet for 18 weeks, with or without a daily bout of treadmill exercise. Rats were then allowed free access to HC/HF diet containing low (0.3%) or high (5.9%) levels of RS. Weight regain, energy balance, body composition, adipocyte cellularity, and fuel utilization were monitored as rats relapsed to obesity and surpassed their original, obese weight.

RESULTS

Both RS and exercise independently attenuated weight regain by reducing the energy gap between the drive to eat and suppressed energy requirements. Exercise attenuated the deposition of lean mass during relapse, whereas its combination with RS sustained lean mass accrual as body weight returned. Early in relapse, RS lowered insulin levels and reduced the deposition of fat in subcutaneous adipose tissue. Exercise cessation at five weeks of relapse led to increased weight gain, body fat, subcutaneous adipocytes, and decreased lean mass; all detrimental consequences to overall metabolic health.

CONCLUSIONS

These data are the first to show the complimentary effects of dietary RS and regular exercise in countering the metabolic drive to regain weight following weight loss and suggest that exercise cessation, in the context of relapse on a HC/HF diet, may have dire metabolic consequences.

Effects of barley β-glucan-enriched flour fractions on the glycaemic index of bread

The aim of this research was to evaluate β-glucan-enriched flours, obtained from barleys with either normal or waxy starch, for their effects on the glycaemic index (GI) and the quality of bread. Rheological results confirmed that when barley flour was included in the dough the overall quality of bread slightly worsened. However, positive consequences on glycaemia were obtained with the normal starch barley: the GI of all-wheat bread (82.8 ± 7.2) was significantly reduced (57.2 ± 7.9) when 40% of wheat flour was substituted with β-glucan-enriched barley flour (6.0% ± 0.1 β-glucan in the final flour blend). In contrast, this positive effect was significantly reduced (GI: 70.1 ± 9.1) when 40% of wheat flour was substituted with the β-glucan-enriched flour of a waxy barley (CDC Alamo; 6.6 ± 0.2 β-glucan in the final flour blend), suggesting that the ability of β-glucans to lower the GI was affected by the barley starch-type.

A high-amylopectin diet caused hepatic steatosis associated with more lipogenic enzymes and increased serum insulin concentration

Starch is the major energy source for monogastric mammals and humans. The present study was conducted to evaluate the liver metabolic responses of weaned pigs fed with different dietary starches. A total of sixteen weaned pigs were fed with two experimental diets containing either cassava starch (CS, 80 % amylopectin and 20 % amylose) or maize starch (70 % amylopectin and 30 % amylose). The present results showed that the growth performance was not affected by different dietary starches (P>0·05). However, ingestion of CS not only increased the lipid content in liver tissues, but also elevated the concentrations of serum cholesterol and insulin (P < 0·05). The metabolic responses induced by CS were associated with more lipogenic enzymes such as fatty acid synthase and 3-hydroxy-3-methyl-glutaryl-CoA reductase in liver (P < 0·05). Real-time PCR quantification for lipid metabolic genes indicated that ingestion of CS not only up-regulated the expression of these lipogenic genes, but also decreased the expression of lipolytic genes. These results suggested that the metabolic responses of weaned pigs fed with different dietary starches may vary widely depending on their composition, and ingestion of starches that are high in amylopectin may produce a stronger insulinaemic response and lead to an up-regulation of lipogenesis in the liver.

Digestion rate of dietary starch affects the systemic circulation of lipid profiles and lipid metabolism-related gene expression in weaned pigs

The present study was conducted to investigate the effect of digestion rate of dietary starch on postprandial systemic circulating glucose, insulin and lipid profiles, and the activity and gene expression of lipid metabolism-related enzymes in weaned pigs. A total of twenty-four weaned pigs, surgically fitted with a catheter in the jugular vein, were randomly assigned to three dietary treatment groups, representing the high digestion rate starch (HDRS) group, the moderate-digestion rate starch (MDRS) group and the low-digestion rate starch (LDRS) group. The amylopectin:amylose ratios in the diets of each group were 27·6:1, 27·6:8·5 and 1:27·6, respectively. The serum concentrations of glucose, TAG, total cholesterol, LDL-cholesterol and HDL-cholesterol in the HDRS group were increased to the peak point at postprandial 1·5, 2·5, 2·5, 1·5 and 1·5 h, those in the MDRS group were at postprandial 2·5, 3·5, 3·5, 3·5 and 3·5 h and those in the LDRS group were at postprandial 2·5, 3·5, 3·5, 1·5 and 3·5 h, respectively. The serum concentration of insulin in the HDRS group was higher (P < 0·05) than those in the MDRS group, and those in the MDRS group was also higher (P < 0·05) than those in the LDRS group at postprandial 0·5, 1·5 and 2·5 h, respectively. The serum concentrations of acetate, propionate and butyrate in the HDRS group were higher (P < 0·05) than those in the MDRS group, and those in the MDRS group were higher (P < 0·05) than in the LDRS group in each feeding cycle, in turn, respectively. The activity of fatty acid synthase (FAS) in the liver and abdominal adipose tissues, that of acetyl CoA carboxylase (ACC) in the myocardium and interscapular brown adipose tissues and that of the ATP-citrate lyase (ATP-CL) in the liver and interscapular brown adipose tissues in pigs of the HDRS group were higher (P < 0·05) than that of the MDRS group. The mRNA levels of FAS in the myocardium, liver and interscapular brown adipose tissues of pigs in the HDRS group were higher (P < 0·05) than those of the MDRS group. The activities and mRNA levels of FAS, ACC and ATP-CL in the myocardium, liver, abdominal and interscapular brown adipose tissues of the HDRS group were higher than those of the LDRS group. We conclude that the digestion rate of dietary starch affected not only the postprandial systemic circulating levels of glucose and insulin but also the lipid metabolism in weaned pigs. Dietary starch with higher digestion rate produces higher blood glucose and insulin response, ameliorates the blood lipid profiles and up-regulates the activity and gene expression profile of lipid metabolism-related genes in weaned pigs.

Triennial Growth Symposium: effects of polymeric carbohydrates on growth and development in pigs

Polymeric carbohydrates, starch and nonstarch polysaccharides (NSP), quantitatively represent the largest portion of the diets for pigs and are, therefore, the largest energy contributor. The 2 types of polysaccharides, however, have different fates and functions in the gastrointestinal tract and lead to different metabolites upon digestion. Pancreatic and mucosal enzymes in the small intestine break down the majority of starch, whereas NSP primarily are degraded by the microflora in the large intestine. Starch degradation leads to the release of glucose, which is absorbed by an active absorption process that triggers the release of insulin from the pancreas, whereas the fermentation of NSP to short-chain fatty acids (SCFA; i.e., acetate, propionate, and butyrate) occurs at a slower and more constant rate and with SCFA being absorbed by passive diffusion. Type and amounts of polymeric carbohydrates influence growth and development through different mechanisms. First, the proportion of starch to NSP plays an important role for the content of available energy (i.e., DE, ME, and NE); available energy relative to protein is crucial for performance and carcass quality. Second, the proportion of starch to NSP will influence rate and type of metabolites (i.e., glucose vs. SCFA) deriving from carbohydrate assimilation. Third and finally, the type of starch (i.e., types A, B, and C) and soluble NSP will influence the release of insulin, the hormone that facilitates nutrient uptake by tissues, organs, and cells, and thus plays a critically essential role in protein synthesis and muscle growth, as well as lipid synthesis and adipose tissue growth. In conclusion, polymeric carbohydrates influence growth and development through events in the gut and direct and indirect effects of different metabolites deriving from carbohydrate assimilation.

A low glycaemic diet improves oral glucose tolerance but has no effect on β-cell function in C57BL/6J mice

AIM

Clinical studies have suggested a role for dietary glycaemic index (GI) in body weight regulation and diabetes risk. Here, we investigated the long-term metabolic effects of low and high glycaemic diets using the C57BL/6J mouse model.

METHODS

Female C57BL/6J mice were fed low or high glycaemic starch in either low-fat or medium-fat diets for 22 weeks. Oral and intravenous glucose tolerance tests were performed to investigate the effect of the experimental diets on glucose tolerance and insulin resistance.

RESULTS

In this study, a high glycaemic diet resulted in impaired oral glucose tolerance compared to a low glycaemic diet. This effect was more pronounced in the group fed a medium-fat diet, suggesting that a lower dietary fat content ameliorates the negative effect of a high glycaemic diet. No effect on body weight or body fat content was observed in either a low-fat diet or a medium-fat diet. Static incubation of isolated islets did not show any differences in basal (3.3 mM glucose) or glucose-stimulated (8.6 and 16.7 mM glucose) insulin secretion between mice fed a low or high glycaemic diet.

CONCLUSION

Together, our data suggest that the impaired glucose tolerance seen after a high glycaemic diet is not explained by altered β-cell function.

Hyperphagia induced by sucrose: relation to circulating and CSF glucose and corticosterone and orexigenic peptides in the arcuate nucleus

Sucrose-rich diets compared to starch-rich diets are known to stimulate overeating under chronic conditions. The present study in normal-weight rats established an acute "preload-to-test meal" paradigm for demonstrating sucrose-induced hyperphagia and investigating possible mechanisms that mediate this behavioral phenomenon. In this acute paradigm, the rats were first given a small (15 kcal) sucrose preload (30% sucrose) for 30 min compared to an equicaloric, starch preload (25% starch with 5% sucrose) and then allowed to freely consume a subsequent test meal of lab chow. The sucrose preload, when compared to a starch preload equal in energy density and palatability, consistently increased food intake in the subsequent test meal occurring between 60 and 120 min after the end of the preload. Measurements of hormones, metabolites and hypothalamic peptides immediately preceding this hyperphagia revealed marked differences between the sucrose vs starch groups that could contribute to the increase in food intake. Whereas the sucrose group compared to the starch group immediately after the preload (at 10 min) had elevated levels of glucose in serum and cerebrospinal fluid (CSF) along with reduced expressions of neuropeptide Y (NPY) and agouti-related protein (AgRP) in the arcuate nucleus (ARC), the subsequent effects (at 30-60 min) just preceding the test meal hyperphagia were the reverse. Along with lower levels of glucose, they included markedly elevated serum and CSF levels of corticosterone and mRNA levels of NPY and AgRP in the ARC. In addition to establishing an animal model for sucrose-induced hyperphagia, these results demonstrate peripheral and central mechanisms that may mediate this behavioral phenomenon.

Consumption of a high glycemic index diet increases abdominal adiposity but does not influence adipose tissue pro-oxidant and antioxidant gene expression in C57BL/6 mice

The hypothesis of this study is that consumption of a high glycemic index (GI) starch will increase adiposity, increase expression of the pro-oxidant enzyme (nicotinamide adenine dinucleotide phosphate [NADPH] oxidase), and decrease expression of the antioxidant enzymes (catalase, glutathione peroxidase [GPx], and superoxide dismutase [SOD]) in adipose tissue of mice. C57BL/6 mice (n = 5-8/group) were fed a diet containing either high-GI starch (100% amylopectin) or low-GI starch (60% amylose/40% amylopectin) under low-fat (LF) or high-fat (HF) conditions for 16 weeks. Meal tolerance tests (MTTs) indicated that the postprandial blood glucose response over 120 minutes for the high-GI mice under LF and HF conditions was significantly greater than for mice fed low-GI diets. This result was not due to increased food consumption by the high-GI mice during the MTT. Although there was no difference in body weight between mice fed high-GI or low-GI starch, LF high-GI mice had significantly greater adiposity compared to LF low-GI mice. High-fat mice had a significant increase in NADPH oxidase expression compared to LF mice, but there was no significant effect of starch on NADPH oxidase expression. High-fat diet significantly decreased the expression of GPx and catalase, but there was no significant effect of starch on GPx and catalase expression. There was no difference in SOD expression among any of the diet groups. In conclusion, high GI diets increase adiposity under LF conditions but do not influence pro-oxidant or antioxidant enzyme gene expression in adipose tissue of C57BL/6 mice.

Nutritional profiles in a public health perspective: a critical review

Nutritional profiling is defined as 'the science of categorizing foods according to their nutritional composition' and it is useful for food labelling and regulation of health claims. The evidence for the link between nutrients and health outcomes was reviewed. A reduced salt intake reduces blood pressure, but only a few randomized controlled trials have verified the effect of salt on overall and cardiovascular mortality. Evidence linking a reduced fat intake with cardiovascular mortality and obesity is generally non-significant. Studies that have examined the relationship between obesity and diet have produced contrasting results. A simulation exercise that demonstrated that the impact of a reduced salt and fat intake on overall mortality would be negligible in the European population was carried out. Consideration of the literature and the results of this simulation exercise suggest that the introduction of nutritional profiles in Europe would be expected to have a very limited impact on health outcomes.

Glycaemic indices of three Sri Lankan wheat bread varieties and a bread-lentil meal

The glycaemic index (GI) concept ranks individual foods and mixed meals according to the blood glucose response. Low-GI foods with a slow and prolonged glycaemic response are beneficial for diabetic people, and several advantages have been suggested also for non-diabetic individuals. The recent investigations imply an increasing prevalence of diabetes mellitus in Sri Lanka. Thus, the present study was designed primarily to determine the glycaemic indices of some bread varieties in Sri Lanka as bread has become a staple diet among most of the urban people. A second objective was to observe the effects of macronutrients and physicochemical properties of starch on GI. Glycaemic responses were estimated according to FAO/WHO guidelines and both glucose and white bread were used as standards. Non-diabetic individuals aged 22-30 years (n=10) participated in the study. The test meals included white sliced bread, wholemeal bread, ordinary white bread and a mixed meal of wholemeal bread with lentil curry. The GI values (+/-standard error of the mean) of the meals were 77+/-6, 77+/-6, 80+/-4, 61+/-6, respectively (with glucose as the standard). The GI values of the bread varieties or the meal did not differ significantly (P >0.05). However, the meal can be categorized as a medium-GI food while the other bread varieties belong to the high-GI food group. A significant negative correlation was obtained with protein (P=0.042) and fat (P=0.039) contents of the food items and GI. Although the GI values of the foods are not significantly different, the inclusion of lentils caused the GI to decrease from a high-GI category to a medium-GI category. According to the present study, a ratio of 1.36 can be used to interconvert the GI values obtained with the two standards.

Influence of the type of indigestible carbohydrate on plasma and urine short-chain fatty acid profiles in healthy human volunteers

BACKGROUND/OBJECTIVES

Health effects of whole grain foods are becoming more evident. In this study, we analysed the short-chain fatty acid profiles in urine and serum derived from the colonic fermentation process of (13)C-barley meals, prepared from barley grown under (13)CO(2) atmosphere.

SUBJECTS/METHODS

In a crossover study, five volunteers ingested intact barley kernels (high content of non-starch polysaccharides (NSP) and resistant starch (RS)) and barley porridge (high content of NSP only). Using a newly developed stable isotope technology, we monitored 14 and 24 h postprandially (13)C-acetate, (13)C-propionate and (13)C-butyrate in plasma and urine, respectively. The oro-cecal transit time (OCTT) of the meals was measured with the hydrogen breath test.

RESULTS

The OCTT was 6 h and did not differ between the two test meals. An increase of (13)C-acetate was observed already early after ingestion of the meals (<6 h) and was attributed to early fermentation of the test meal. A rise in plasma (13)C-propionate in the fermentation phase could only be detected after the porridge and not after the kernel meal. An increase in (13)C-butyrate was only found in the fermentation phase and was higher after the barley kernels. Urine (13)C-short-chain fatty acids data were consistent with these observations.

CONCLUSIONS

The difference in the profiles of (13)C-acetate, (13)C-propionate and (13)C-butyrate indicates that NSP combined with RS results in an altered fermentation profile than dietary fibre alone.

Resistant starch improves insulin sensitivity in metabolic syndrome

AIMS

Diets rich in non-viscous fibre are linked to a reduced risk of both diabetes and cardiovascular disease; however, the mechanism of action remains unclear. This study was undertaken to assess whether chronic consumption of this type of fibre in individuals with the metabolic syndrome would improve insulin sensitivity via changes in ectopic fat storage.

METHODS

The study was a single-blind, randomized, parallel nutritional intervention where 20 insulin resistant subjects consumed either the fibre supplement (resistant starch) (40 g/day) or placebo supplement (0 g/day) for 12 weeks. Insulin sensitivity was measured by euglycaemic-hyperinsulinaemic clamp and ectopic fat storage measured by whole-body magnetic resonance spectroscopy.

RESULTS

Resistant starch consumption did not significantly affect body weight, fat storage in muscle, liver or visceral depots. There was also no change with resistant starch feeding on vascular function or markers of inflammation. However, in subjects randomized to consume the resistant starch, insulin sensitivity improved compared with the placebo group (P = 0.023). Insulin sensitivity correlated significantly with changes in waist circumference and fat storage in tibialis muscle and to a lesser extent to visceral-to-subcutaneous abdominal adipose tissue ratio.

CONCLUSION

Consumption of resistant starch improves insulin sensitivity in subjects with the metabolic syndrome. Unlike in animal models, diabetes prevention does not appear to be directly related to changes in body adiposity, blood lipids or inflammatory markers. Further research to elucidate the mechanisms behind this change in insulin sensitivity in human subjects is required.

Impairment of fat oxidation under high- vs. low-glycemic index diet occurs before the development of an obese phenotype

Exposure to high vs. low glycemic index (GI) diets increases fat mass and insulin resistance in obesity-prone C57BL/6J mice. However, the longer-term effects and potentially involved mechanisms are largely unknown. We exposed four groups of male C57BL/6J mice (n = 10 per group) to long-term (20 wk) or short-term (6 wk) isoenergetic and macronutrient matched diets only differing in starch type and as such GI. Body composition, liver fat, molecular factors of lipid metabolism, and markers of insulin sensitivity and metabolic flexibility were investigated in all four groups of mice. Mice fed the high GI diet showed a rapid-onset (from week 5) marked increase in body fat mass and liver fat, a gene expression profile in liver consistent with elevated lipogenesis, and, after long-term exposure, significantly reduced glucose clearance following a glucose load. The long-term high-GI diet also led to a delayed switch to both carbohydrate and fat oxidation in the postprandial state, indicating reduced metabolic flexibility. In contrast, no difference in carbohydrate oxidation was observed after short-term high- vs. low-GI exposure. However, fatty acid oxidation was significantly blunted as early as 3 wk after beginning of the high-GI intervention, at a time where most measured phenotypic markers including body fat mass were comparable between groups. Thus long-term high-GI feeding resulted in an obese, insulin-resistant, and metabolically inflexible phenotype in obesity-prone C57BL/6J mice. Early onset and significantly impaired fatty acid oxidation preceded these changes, thereby indicating a potentially causal involvement.

Metabolic effects of diets differing in glycaemic index depend on age and endogenous glucose-dependent insulinotrophic polypeptide in mice

AIMS/HYPOTHESIS

High- vs low-glycaemic index (GI) diets unfavourably affect body fat mass and metabolic markers in rodents. Different effects of these diets could be age-dependent, as well as mediated, in part, by carbohydrate-induced stimulation of glucose-dependent insulinotrophic polypeptide (GIP) signalling.

METHODS

Young-adult (16 weeks) and aged (44 weeks) male wild-type (C57BL/6J) and GIP-receptor knockout (Gipr ( -/- )) mice were exposed to otherwise identical high-carbohydrate diets differing only in GI (20-26 weeks of intervention, n = 8-10 per group). Diet-induced changes in body fat distribution, liver fat, locomotor activity, markers of insulin sensitivity and substrate oxidation were investigated, as well as changes in the gene expression of anorexigenic and orexigenic hypothalamic factors related to food intake.

RESULTS

Body weight significantly increased in young-adult high- vs low-GI fed mice (two-way ANOVA, p < 0.001), regardless of the Gipr genotype. The high-GI diet in young-adult mice also led to significantly increased fat mass and changes in metabolic markers that indicate reduced insulin sensitivity. Even though body fat mass also slightly increased in high- vs low-GI fed aged wild-type mice (p < 0.05), there were no significant changes in body weight and estimated insulin sensitivity in these animals. However, aged Gipr ( -/- ) vs wild-type mice on high-GI diet showed significantly lower cumulative net energy intake, increased locomotor activity and improved markers of insulin sensitivity.

CONCLUSIONS/INTERPRETATION

The metabolic benefits of a low-GI diet appear to be more pronounced in younger animals, regardless of the Gipr genotype. Inactivation of GIP signalling in aged animals on a high-GI diet, however, could be beneficial.