Carbohydrate-free Diet Research Articles

Effects of medium-chain triglycerides on gluconeogenesis and ureagenesis in weaned rats fed a high fat diet

We explored the effects of Medium-chain triglycerides (MCT) on gluconeogenesis and ureagenesis in the liver of weaned male rats fed high fat, carbohydrate-free diets. The rats of three experimental groups and control were fed for 10 days. The diets were high fat, carbohydrate-free diets consisting either of a corn oil or MCT, and high protein carbohydrate-free diet and a control (high carbohydrate) diet. The hepatic glucose-6-phosphatase (G6Pase) activity increased in the experimental groups. Despite the elevated G6Pase activity in these groups, hepatic activities of glutamic alanine transaminase (GAT), pyruvate carboxylase (PC) and arginase differed among the experimental groups. The HF-corn oil rats showed elevation of PC activity, but no elevation of GAT activity, and the lowest arginase activity among the three groups. The HF-MCT diet-fed rats showed higher GAT and arginase activities than the HF-corn oil group. In the HP diet-fed rats, GAT and arginase activities enhanced, PC did not.

The regulation of gluconeogenesis in the Siberian sturgeon (Acipenser baerii) affected later in life by a short-term high-glucose programming during early life

Abstract We undertook this study to determine whether an acute glucose stimulus during first feeding period and dietary carbohydrates can modify the gluconeogenesis pathway in the Siberian sturgeon (Acipenser baerii). The sturgeon larvae were fed a high glucose diet (57% glucose, 21.5% protein) or a carbohydrate-free diet (67.7% protein) from first feeding to yolk absorption (8–12 days post-hatching, dph). At 13 dph, each group of fish was assigned to two treatments. One group was fed a high-carbohydrate diet (35% dextrin, 39.3% protein), and the other group was fed a carbohydrate-free diet until the 20th wk. The results indicated that the high carbohydrate intake inhibited mRNA expression and activity of gluconeogenic enzymes at 13, 30 dph and the 20th wk. The early high glucose stimulus depressed final body weight of sturgeon at 13, 30 dph and the 20th wk. This stimulus also inhibited mRNA expressions of fructose-1,6-bisphosphatase at 30 dph and increased mRNA expressions of phosphoenolpyruvate carboxykinase cytosolic forms and glucose-6-phosphatase (G6Pase), while it inhibited activities of G6Pase at 20th wk when the fish were fed a carbohydrate-free diet. Results suggested that the Siberian sturgeon could regulate gluconeogenesis pathway response to dietary carbohydrates content at both transcriptional and post-translational levels. High glucose low protein intake during first feeding disturbs gluconeogenesis regulation in later life. However, the Siberian sturgeon might have a capacity to adapt to later nutritional conditions by reversing the changes in the gluconeogenesis pathway which induced by early stimulation at the transcriptional level during the 20 weeks feeding.

Comparison of a carbohydrate-free diet vs. fasting on plasma glucose, insulin and glucagon in type 2 diabetes

ObjectiveHyperglycemia improves when patients with type 2 diabetes are placed on a weight-loss diet. Improvement typically occurs soon after diet implementation. This rapid response could result from low fuel supply (calories), lower carbohydrate content of the weight-loss diet, and/or weight loss per se. To differentiate these effects, glucose, insulin, C-peptide and glucagon were determined during the last 24h of a 3-day period without food (severe calorie restriction) and a calorie-sufficient, carbohydrate-free diet. Research designSeven subjects with untreated type 2 diabetes were studied. A randomized-crossover design with a 4-week washout period between arms was used. MethodsResults from both the calorie-sufficient, carbohydrate-free diet and the 3-day fast were compared with the initial standard diet consisting of 55% carbohydrate, 15% protein and 30% fat. ResultsThe overnight fasting glucose concentration decreased from 196 (standard diet) to 160 (carbohydrate-free diet) to 127mg/dl (fasting). The 24h glucose and insulin area responses decreased by 35% and 48% on day 3 of the carbohydrate-free diet, and by 49% and 69% after fasting. Overnight basal insulin and glucagon remained unchanged. ConclusionsShort-term fasting dramatically lowered overnight fasting and 24h integrated glucose concentrations. Carbohydrate restriction per se could account for 71% of the reduction. Insulin could not entirely explain the glucose responses. In the absence of carbohydrate, the net insulin response was 28% of the standard diet. Glucagon did not contribute to the metabolic adaptations observed.

Microarray Analysis After Preoperative Dietary Restriction Reveals Potential Mechanisms Involved in the Protection Against Ischemia-Reperfusion Injury.

Background. Ischemia-reperfusion injury (IRI) is inevitable during kidney transplantation and leads to oxidative stress and inflammation. We previously reported that short-term preoperative dietary restriction (DR), 3-day fasting and protein-free diets protect against renal IRI while a fat-free or carbohydrate-free (CHO-free) diet do not. To understand underlying mechanisms, we performed microarrays and compared gene expression profiles of (non)-protective diets in search for pathways involved in the effect. Methods. Male C57BL/6 mice were randomized to preoperative normal food or: 2 weeks 30%DR, 3-day fasting, 3-day protein-free, 3-day CHO-free or 3-day fat-free diet. Kidneys were harvested after each diet. Gene expressions were analysed by Affymetrix array and pathway analysis was done with Ingenuity. Cut-off for significance was set on fold change ≥1.5 and p-value <0.05. Results. Compared to ad libitum fed, 2 weeks 30%DR resulted in 492 differentially expressed genes (DEG). Similarly, 3-day fasting led to 2604 DEG and a protein-free diet to 391 DEG. The fat-free diet resulted in zero DEG and a CHO-free diet in 1717 DEG. Seventy DEG overlapped in all 3 protective diets, with an overlap of 30 with CHO-free. Ingenuity analysis revealed the involvement of metabolic processes like retinol biosynthesis as well as stress responses like Nrf2-pathway. Preliminary in depth analysis shows differences in these pathways between the protective diets and CHO-free, in which genes like txnip and mrp1 may play a central role. Conclusions. This unique microarray dataset of different dietary interventions points to the involvement of pathways related to oxidative stress resistance and retinol metabolism in the beneficial effects against renal IRI. Since the non-protective CHO-free diet also induced activation of these pathways, further exploration is needed. Collectively, these data suggest that a combined action of both metabolic and stress resistance pathways results in protection against IRI given by preoperative dietary interventions.

Nervous glucose sensing regulates postnatal β cell proliferation and glucose homeostasis.

How glucose sensing by the nervous system impacts the regulation of β cell mass and function during postnatal development and throughout adulthood is incompletely understood. Here, we studied mice with inactivation of glucose transporter 2 (Glut2) in the nervous system (NG2KO mice). These mice displayed normal energy homeostasis but developed late-onset glucose intolerance due to reduced insulin secretion, which was precipitated by high-fat diet feeding. The β cell mass of adult NG2KO mice was reduced compared with that of WT mice due to lower β cell proliferation rates in NG2KO mice during the early postnatal period. The difference in proliferation between NG2KO and control islets was abolished by ganglionic blockade or by weaning the mice on a carbohydrate-free diet. In adult NG2KO mice, first-phase insulin secretion was lost, and these glucose-intolerant mice developed impaired glucagon secretion when fed a high-fat diet. Electrophysiological recordings showed reduced parasympathetic nerve activity in the basal state and no stimulation by glucose. Furthermore, sympathetic activity was also insensitive to glucose. Collectively, our data show that GLUT2-dependent control of parasympathetic activity defines a nervous system/endocrine pancreas axis that is critical for β cell mass establishment in the postnatal period and for long-term maintenance of β cell function.

Effects of a short interval carbohydrate free diet on tissue FDG uptake

Purpose: Tight glucose control is essential for 18-Fludeoxyglucose (18F-FDG) positron emission tomography (PET) imaging. A strategy to ensure appropriate glucose levels is to advise a carbohydrate free diet prior to scanning. This alters glucose metabolism which can have ramifications on tissue FDG biodistribution. The aim of this study is to evaluate the effects of advising a carbohydrate free diet for two days prior to PET scan on FDG uptake in the liver, heart, bone marrow, skeletal muscle and tumor. Materials and methods: All patients at an outpatient facility were advised to maintain a diet free of carbohydrates for two days prior to 18F- FDG PET/Computed tomography (CT) scanning to maintain glucose control at the time of the scan. Self reported adherence to the diet was recorded by the scheduling coordinator on the day of imaging. A retrospective analysis of 228 consecutive 18F-FDG PET/CT scans was performed in which the maximum standardized uptake value (max SUV) was recorded for the following six sites: right and left hepatic lobes, left ventricle of the heart, sacrum, thigh and tumor. The max SUV of the patients who adhered to the diet (n=144) were compared with those who did not (n=85). Results: The average max SUV for the right and left hepatic lobes and the left ventricle were 3.93±0.78, 3.70±0.76 and 6.34±5.12 for the adherent patients and 3.63±0.84, 3.41±0.80 and 6.98±4.69 for the non-adherent patients. The average max SUV in the hepatic lobes of the adherent group was statistically significantly higher by 8.2% in the right lobe and 8.8% in left lobe when compared with the non-adherent group ( p <0.003). The average max SUV in the heart of the adherent group was statistically significantly lower by 10% when compared with the non-adherent group ( p <0.040). No significant difference was observed in the remaining tissues, including tumor. Conclusions: Altering carbohydrate intake can significantly affect the metabolic milieu (FDG biodistribution in normal tissues). The liver max SUV in patients on a carbohydrate free diet prior to PET scanning was higher than those who were not. This difference should be kept in mind when defining a normal cut off threshold SUV in the liver.

Estrogen Deficiency Aggravates Insulin Resistance and Induces β-Cell Loss and Diabetes in Female New Zealand Obese Mice

In several rodent strains such as the New Zealand Obese (NZO) mouse, the incidence of obesity-associated diabetes mellitus is much higher in males than in females. In the present study, we investigated the effects of ovariectomy on glucose homeostasis in female NZO mice in order to elucidate the mechanism of their diabetes resistance. NZO females were ovariectomized at the age of 4 weeks, received a high-fat diet and body weight, body fat, glucose and insulin tolerance were investigated in comparison to sham-operated mice. In a second experiment, operated mice were fed a carbohydrate-free diet up to the age of 19 weeks before they received the high-fat diet. In comparison with a sham-operated control group, ovariectomized female NZO mice exhibited similar body weights, a reduced glucose tolerance, developed significantly higher blood glucose levels, lost insulin producing β-cells, which finally resulted in a diabetes prevalence of 73% at the age of 16 weeks vs. 25% in controls. Similar to male NZO mice, ovariectomized females presented a more severe insulin resistance in the insulin tolerance test than sham-operated controls. Furthermore, the more severe insulin resistance in ovariectomized mice preceded the development of diabetes and pancreatic insulin depletion that was caused by a dietary regimen of carbohydrate restriction and subsequent re-exposure. In summary our data demonstrate that estrogen protects NZO females from β-cell loss and obesity-associated diabetes mellitus. This effect is due to a reduced insulin resistance and possibly also to a reduced sensitivity of β-cells to glucolipotoxic conditions.

Increased Glyceride–Glycerol Synthesis in Liver and Brown Adipose Tissue of Rat: In‐Vivo Contribution of Glycolysis and Glyceroneogenesis

We have previously shown that a high-protein, carbohydrate-free diet can decrease the production of glycerol-3-phosphate (G3P) from glucose and increase glyceroneogenesis in both brown (BAT) and epididymal (EAT) adipose tissue. Here, we utilized an in-vivo approach to examine the hypothesis that there is reciprocal regulation in the G3P synthesis from glucose (via glycolysis) and glyceroneogenesis in BAT, EAT and liver of fasted rats and cafeteria diet-fed rats. Glyceroneogenesis played a prominent role in the generation of G3P in the liver (~70%) as well as in BAT and EAT (~80%) in controls rats. The cafeteria diet induced an increase in the total glyceride-glycerol synthesis and G3P synthesis from glucose and a decrease in glyceroneogenesis in BAT; this diet did not affect either the total glyceride-glycerol synthesis or G3P generation from glyceroneogenesis or glycolysis in the liver or EAT. Fasting induced an increase in total glyceride-glycerol synthesis and glyceroneogenesis and a decrease in G3P synthesis from glucose in the liver but did not affect either the total glyceride-glycerol synthesis or G3P synthesis from glyceroneogenesis in BAT and EAT, despite a reduction in glycolysis in these tissues. These data demonstrate that reciprocal changes in the G3P generation from glucose and from glyceroneogenesis in the rat liver and BAT occur only when the synthesis of glycerides-glycerol is increased. Further, our data suggest that this increase may be essential for the systemic recycling of fatty acids by the liver from fasted rats and for the maintenance of the thermogenic capacity of BAT from cafeteria diet-fed rats.

Response of C57Bl/6 mice to a carbohydrate-free diet

High fat feeding in rodents generally leads to obesity and insulin resistance whereas in humans this is only seen if dietary carbohydrate is also high, the result of the anabolic effect of poor regulation of glucose and insulin. A previous study of C57Bl/6 mice (Kennedy AR, et al.: Am J Physiol Endocrinol Metab (2007) 262 E1724-1739) appeared to show the kind of beneficial effects of calorie restriction that is seen in humans but that diet was unusually low in protein (5%). In the current study, we tested a zero-carbohydrate diet that had a higher protein content (20%). Mice on the zero-carbohydrate diet, despite similar caloric intake, consistently gained more weight than animals consuming standard chow, attaining a dramatic difference by week 16 (46.1 ± 1.38 g vs. 30.4 ± 1.00 g for the chow group). Consistent with the obese phenotype, experimental mice had fatty livers and hearts as well as large fat deposits in the abdomino-pelvic cavity, and showed impaired glucose clearance after intraperitoneal injection. In sum, the response of mice to a carbohydrate-free diet was greater weight gain and metabolic disruptions in distinction to the response in humans where low carbohydrate diets cause greater weight loss than isocaloric controls. The results suggest that rodent models of obesity may be most valuable in the understanding of how metabolic mechanisms can work in ways different from the effect in humans.

Impact de la maladie parodontale sur la pression artérielle des souris diabétiques

Diabetes-driven cardiovascular diseases represent a high challenge for developed countries. Periodontal disease is strictly linked to the aforementioned diseases, due to its Gram negative–driven inflammation. Thus, we investigated the effects of periodontal disease on arterial pressure during the development of diabetes in mice. To this aim, C57BL/6 female mice were colonized with pathogens of periodontal tissue (Porphyromonas gingivalis, Prevotella intermedia and Fusobacterium nucleatum) for 1month, whereas another group of mice did not undergo the colonization. Subsequently, all mice were fed a high-fat carbohydrate-free diet for 3months. Then, arterial pressure was measured in vivo and a tomodensitometric analysis of mandibles was realized as well. Our results show increased mandibular bone-loss induced by colonization with periopathogens. In addition, periodontal infection augmented glucose-intolerance and systolic and diastolic arterial pressure, parameters already known to be affected by a fat-diet. In conclusion, we show here that periodontal disease amplifies metabolic troubles and deregulates arterial pressure, emerging as a new axis of metabolic investigation.

Carbon isotopes in exhaled breath track metabolic substrates in brown bears (Ursus arctos)

Abstract Dietary carbon is oxidized and exhaled as CO2, thus δ13Cbreath values can provide information on diet and substrate use for energy. However, physiological phenomena such as fat deposition and fasting can alter values of δ13Cbreath such that interpretation of source contributions may be unclear. Consequently, before application to free-ranging animals, inferences about feeding and nutritional states based on δ13Cbreath should be validated with controlled experiments using captive individuals. Here, we report δ13Cbreath values for 4 captive brown bears (Ursus arctos) under different conditions: the bears were 1st given a diet containing carbohydrate, lipid, and protein; they were then switched to a carbohydrate-free diet consisting of salmon and fish oil; and finally they were placed on a fast leading to winter hibernation. Following the switch to the carbohydrate-free diet, values of δ13Cbreath and δ13Cplasma suggested that although oxidation included a substantial portion of dietary proteins, die...

Against the stream: relevance of gluconeogenesis from fatty acids for natives of the arctic regions

Background. The question whether even-chain fatty acids can be converted into glucose has a long-standing tradition in biochemistry. Since the glyoxylate shunt is absent from mammals, the question has been considered to be solved. It is of particular relevance for understanding the metabolic state of natives of the arctic regions due to the very high fat content of their traditional diet only containing negligible amounts of carbohydrates.Methods & Results. Using an in silico approach, we discovered several hitherto unknown routes in human metabolism that allow the conversion of even-chain fatty acids into carbohydrates in humans. These pathways proceed via ketogenesis over the intermediate of acetone and produce the gluconeogenic precursor pyruvate. While these pathways can make a contribution to glucose production during times of limited carbohydrate supply, we found that their capacity might be limited due to a high demand in reducing equivalents in acetone degradation. Considering the traditional diet of natives of the arctic regions, the detected pathways are not only important in order to improve carbohydrate supply, but moreover reduce the amount of protein that needs to be used for gluconeogenesis.Conclusion. In summary, our study sheds new light on our understanding of the metabolic state of natives from the arctic regions on their traditional diet. Moreover, they provide an avenue for new analyses that can reveal how humans have adapted metabolically to a practically carbohydrate-free diet.

Response of C57Bl/6 mice to a carbohydrate-free diet

High fat feeding in rodents generally leads to obesity and insulin resistance whereas in humans this is only seen if dietary carbohydrate is also high, the result of the anabolic effect of poor regulation of glucose and insulin. A previous study of C57Bl/6 mice (Kennedy AR, et al.: Am J Physiol Endocrinol Metab (2007) 262 E1724-1739) appeared to show the kind of beneficial effects of calorie restriction that is seen in humans but that diet was unusually low in protein (5%). In the current study, we tested a zero-carbohydrate diet that had a higher protein content (20%). Mice on the zero-carbohydrate diet, despite similar caloric intake, consistently gained more weight than animals consuming standard chow, attaining a dramatic difference by week 16 (46.1 ± 1.38 g vs. 30.4 ± 1.00 g for the chow group). Consistent with the obese phenotype, experimental mice had fatty livers and hearts as well as large fat deposits in the abdomino-pelvic cavity, and showed impaired glucose clearance after intraperitoneal injection. In sum, the response of mice to a carbohydrate-free diet was greater weight gain and metabolic disruptions in distinction to the response in humans where low carbohydrate diets cause greater weight loss than isocaloric controls. The results suggest that rodent models of obesity may be most valuable in the understanding of how metabolic mechanisms can work in ways different from the effect in humans.

Metabolic adaptation to a high-fat diet is associated with a change in the gut microbiota

ObjectiveThe gut microbiota, which is considered a causal factor in metabolic diseases as shown best in animals, is under the dual influence of the host genome and nutritional environment. This...

Demonstration of diet-induced decoupling of fatty acid and cholesterol synthesis by combining gene expression array and2H2O quantification

The liver is a crossroad for metabolism of lipid and carbohydrates, with acetyl-CoA serving as an important metabolic intermediate and a precursor for fatty acid and cholesterol biosynthesis pathways. A better understanding of the regulation of these pathways requires an experimental approach that provides both quantitative metabolic flux measurements and mechanistic insight. Under conditions of high carbohydrate availability, excess carbon is converted into free fatty acids and triglyceride for storage, but it is not clear how excessive carbohydrate availability affects cholesterol biosynthesis. To address this, C57BL/6J mice were fed either a low-fat, high-carbohydrate diet or a high-fat, carbohydrate-free diet. At the end of the dietary intervention, the two groups received (2)H(2)O to trace de novo fatty acid and cholesterol synthesis, and livers were collected for gene expression analysis. Expression of lipid and glucose metabolism genes was determined using a custom-designed pathway focused PCR-based gene expression array. The expression analysis showed downregulation of cholesterol biosynthesis genes and upregulation of fatty acid synthesis genes in mice receiving the high-carbohydrate diet compared with the carbohydrate-free diet. In support of these findings, (2)H(2)O tracer data showed that fatty acid synthesis was increased 10-fold and cholesterol synthesis was reduced by 1.6-fold in mice fed the respective diets. In conclusion, by applying gene expression analysis and tracer methodology, we show that fatty acid and cholesterol synthesis are differentially regulated when the carbohydrate intake in mice is altered.

Glucose deprivation in tuberous sclerosis complex-related tumors

BackgroundCancer cells possess unique metabolic phenotypes that are determined by their underlying oncogenic pathways. Activation of the PI3K/Akt/mTOR signaling cascade promotes glycolysis and leads to glucose-dependence in tumors. In particular, cells with constitutive mTORC1 activity secondary to the loss of TSC1/TSC2 function are prone to undergo apoptosis upon glucose withdrawal in vitro, but this concept has not been tested in vivo. This study examines the effects of restricting glucose metabolism by pharmacologic and dietary means in a tuberous sclerosis complex (TSC) tumor xenograft model.ResultsTumor-bearing mice were randomly assigned to receive unrestricted carbohydrate-free ("Carb-free") or Western-style diet in the absence or presence of 2-deoxyglucose (2-DG) in one of four treatment groups. After 14 weeks, tumor sizes were significantly different among the four treatment groups with those receiving 2-DG having the smallest tumors. Unexpectedly, the "Carb-free" diet was associated with the largest tumors but they remained responsive to 2-DG. PET imaging showed significant treatment-related changes in tumor 18fluorodeoxyglucose-uptake but the standard uptake values did not correlate with tumor size. Alternative energy substrates such as ketone bodies and monounsaturated oleic acid supported the growth of the Tsc2-/- cells in vitro, whereas saturated palmitic acid was toxic. Correspondingly, tumors in the high-fat, "Carb-free" group showed greater necrosis and liquefaction that contributed to their larger sizes. In contrast, 2-DG treatment significantly reduced tumor cell proliferation, increased metabolic stress (i.e., ketonemia) and AMPK activity, whereas rapamycin primarily reduced cell size.ConclusionsOur data support the concept of glycolytic inhibition as a therapeutic approach in TSC whereas dietary withdrawal of carbohydrates was not effective.

In Silico Evidence for Gluconeogenesis from Fatty Acids in Humans

The question whether fatty acids can be converted into glucose in humans has a long standing tradition in biochemistry, and the expected answer is “No”. Using recent advances in Systems Biology in the form of large-scale metabolic reconstructions, we reassessed this question by performing a global investigation of a genome-scale human metabolic network, which had been reconstructed on the basis of experimental results. By elementary flux pattern analysis, we found numerous pathways on which gluconeogenesis from fatty acids is feasible in humans. On these pathways, four moles of acetyl-CoA are converted into one mole of glucose and two moles of CO2. Analyzing the detected pathways in detail we found that their energetic requirements potentially limit their capacity. This study has many other biochemical implications: effect of starvation, sports physiology, practically carbohydrate-free diets of inuit, as well as survival of hibernating animals and embryos of egg-laying animals. Moreover, the energetic loss associated to the usage of gluconeogenesis from fatty acids can help explain the efficiency of carbohydrate reduced and ketogenic diets such as the Atkins diet.

Quantifying cholesterol synthesis in vivo using 2H2O: enabling back-to-back studies in the same subject

The advantages of using (2)H(2)O to quantify cholesterol synthesis include i) homogeneous precursor labeling, ii) incorporation of (2)H via multiple pathways, and iii) the ability to perform long-term studies in free-living subjects. However, there are two concerns. First, the t(1/2) of tracer in body water presents a challenge when there is a need to acutely replicate measurements in the same subject. Second, assumptions are made regarding the number of hydrogens (n) that are incorporated during de novo synthesis. Our primary objective was to determine whether a step-based approach could be used to repeatedly study cholesterol synthesis a subject. We observed comparable changes in the (2)H-labeling of plasma water and total plasma cholesterol in African-Green monkeys that received five oral doses of (2)H(2)O, each dose separated by one week. Similar rates of cholesterol synthesis were estimated when comparing data in the group over the different weeks, but better reproducibility was observed when comparing replicate determinations of cholesterol synthesis in the same nonhuman primate during the respective dosing periods. Our secondary objective was to determine whether n depends on nutritional status in vivo; we observed n of ∼25 and ∼27 in mice fed a high-carbohydrate (HC) versus carbohydrate-free (CF) diet, respectively. We conclude that it is possible to acutely repeat studies of cholesterol synthesis using (2)H(2)O and that n is relatively constant.

Carbohydrate-Free Diet Prevents Increase in Bacterial Density and Bacterial Translocation in an Experimental Model of Bacterial Overgrowth

Carbohydrate-Free Diet Prevents Increase in Bacterial Density and Bacterial Translocation in an Experimental Model of Bacterial Overgrowth

Dissociation of lipotoxicity and glucotoxicity in a mouse model of obesity associated diabetes: role of forkhead box O1 (FOXO1) in glucose-induced beta cell failure

Aims/hypothesisCarbohydrate-free diet prevents hyperglycaemia and beta cell destruction in the New Zealand Obese (NZO) mouse model. Here we have used a sequential dietary regimen to dissociate the effects of obesity and hyperglycaemia on beta cell function and integrity, and to study glucose-induced alterations of key transcription factors over 16 days.MethodsMice were rendered obese by feeding a carbohydrate-free diet for 18 weeks. Thereafter, a carbohydrate-containing diet was given. Plasma glucose, plasma insulin and total pancreatic insulin were determined, and forkhead box O1 protein (FOXO1) phosphorylation and the transcription factors pancreatic and duodenal homeobox 1 (PDX1), NK6 homeobox 1 protein (NKX6.1) and v-maf musculoaponeurotic fibrosarcoma oncogene family, protein A (avian) (MAFA) were monitored by immunohistochemistry for 16 days.ResultsDietary carbohydrates produced a rapid and continuous increase in plasma glucose in NZO mice between day 2 and 16 after the dietary challenge. Hyperglycaemia caused a dramatic dephosphorylation of FOXO1 at day 2, followed by a progressive depletion of insulin stores. The loss of beta cells was triggered by apoptosis (detectable at day 8), associated with reduction of crucial transcription factors (PDX1, NKX6.1 and MAFA). Incubation of isolated islets from carbohydrate-restricted NZO mice or MIN6 cells with palmitate and glucose for 48 h resulted in a dephosphorylation of FOXO1 and thymoma viral proto-oncogene 1 (AKT) without changing the protein levels of both proteins.Conclusions/interpretationThe dietary regimen dissociates the effects of obesity (lipotoxicity) from those of hyperglycaemia (glucotoxicity) in NZO mice. Obese NZO mice are unable to compensate for the carbohydrate challenge by increasing insulin secretion or synthesising adequate amounts of insulin. In response to the hyperglycaemia, FOXO1 is dephosphorylated, leading to reduced levels of beta cell-specific transcription factors and to apoptosis of the cells.Electronic supplementary materialThe online version of this article (doi:10.1007/s00125-010-1973-8) contains supplementary material, which is available to authorised users.