Low-carbohydrate diet disrupts the association between insulin resistance and weight gain

Dietary Carbohydrate as Glycemic Load, Not Fat, Coupled with Genetic Permissiveness Favoring Rapid Growth and Extra Calories, Dictate Metabolic Syndrome and Diabetes Induction in Nile Rats (Arvicanthis niloticus)

Objective: Whether dietary carbohydrate (CHO) or fat is more involved in type 2 diabetes (T2DM) induction uncomplicated by dietary fiber was addressed in a spontaneous diabetic model, the diurnal Nile rat that mimics the human condition. Methods: A total of 138 male Nile rats were fed plant-based and animal-based saturated fat where 10% energy as CHO and fat were exchanged across 5 diets keeping protein constant, from 70:10:20 to 20:60:20 as CHO:fat:protein %energy. Diabetes induction was analyzed by: 1. diet composition, i.e., CHO:fat ratio, to study the impact of diet; 2. quintiles of average caloric intake per day to study the impact of calories; 3. quintiles of diabetes severity to study the epigenetic impact on diabetes resistance. Results: High glycemic load (GLoad) was most problematic if coupled with high caloric consumption. Diabetes severity highlighted rapid growth and caloric intake as likely epigenetic factors distorting glucose metabolism. The largest weanling rats ate more, grew faster, and developed more diabetes when the dietary GLoad exceeded their gene-based metabolic capacity for glucose disposal. Diabetes risk increased for susceptible rats when energy intake exceeded 26 kcal/day and the GLoad was >175/2000 kcal of diet and when the diet provided >57% energy as CHO. Most resistant rats ate <25 kcal/day independent of the CHO:fat diet ratio or the GLoad adjusted to body size. Conclusion: Beyond the CHO:fat ratio and GLoad, neither the type of fat nor the dietary polyunsaturated/saturated fatty acid (P/S) ratio had a significant impact, suggesting genetic permissiveness affecting caloric and glucose intake and glucose disposition were key to modulating Nile rat diabetes. Fat became protective by limiting GLoad when it contributed >40% energy and displaced CHO to <50% energy, thereby decreasing the number of diabetic rats and diabetes severity.

Genetic Permissiveness and Dietary Glycemic Load Interact to Predict Type-II Diabetes in the Nile rat (Arvicanthis niloticus)

Objective: The Nile rat (Arvicanthis niloticus) is a superior model for Type-II Diabetes Mellitus (T2DM) induced by diets with a high glycemic index (GI) and glycemic load (GLoad). To better define the age and gender attributes of diabetes in early stages of progression, weanling rats were fed a high carbohydrate (hiCHO) diet for between 2 to 10 weeks. Methods: Data from four experiments compared two diabetogenic semipurified diets (Diet 133 (60:20:20, as % energy from CHO, fat, protein with a high glycemic load (GLoad) of 224 per 2000 kcal) versus Diets 73 MBS or 73 MB (70:10:20 with or without sucrose and higher GLoads of 259 or 295, respectively). An epidemiological technique was used to stratify the diabetes into quintiles of blood glucose (Q1 to Q5), after 2–10 weeks of dietary induction in 654 rats. The related metagenetic physiological growth and metabolic outcomes were related to the degree of diabetes based on fasting blood glucose (FBG), random blood glucose (RBG), and oral glucose tolerance test (OGTT) at 30 min and 60 min. Results: Experiment 1 (Diet 73MBS) demonstrated that the diabetes begins aggressively in weanlings during the first 2 weeks of a hiCHO challenge, linking genetic permissiveness to diabetes susceptibility or resistance from an early age. In Experiment 2, ninety male Nile rats fed Diet 133 (60:20:20) for 10 weeks identified two quintiles of resistant rats (Q1,Q2) that lowered their RBG between 6 weeks and 10 weeks on diet, whereas Q3–Q5 became progressively more diabetic, suggesting an ongoing struggle for control over glucose metabolism, which either stabilized or not, depending on genetic permissiveness. Experiment 3 (32 males fed 70:10:20) and Experiment 4 (30 females fed 60:20:20) lasted 8 weeks and 3 weeks respectively, for gender and time comparisons. The most telling link between a quintile rank and diabetes risk was telegraphed by energy intake (kcal/day) that established the cumulative GLoad per rat for the entire trial, which was apparent from the first week of feeding. This genetic permissiveness associated with hyperphagia across quintiles was maintained throughout the study and was mirrored in body weight gain without appreciable differences in feed efficiency. This suggests that appetite and greater growth rate linked to a fiber-free high GLoad diet were the dominant factors driving the diabetes. Male rats fed the highest GLoad diet (Diet 73MB 70:10:20, GLoad 295 per 2000 kcal for 8 weeks in Experiment 3], ate more calories and developed diabetes even more aggressively, again emphasizing the Cumulative GLoad as a primary stressor for expressing the genetic permissiveness underlying the diabetes. Conclusion: Thus, the Nile rat model, unlike other rodents but similar to humans, represents a superior model for high GLoad, low-fiber diets that induce diabetes from an early age in a manner similar to the dietary paradigm underlying T2DM in humans, most likely originating in childhood.

The Nile Rat (Arvicanthis niloticus) as a Superior Carbohydrate-Sensitive Model for Type 2 Diabetes Mellitus (T2DM)

Type II diabetes mellitus (T2DM) is a multifactorial disease involving complex genetic and environmental interactions. No single animal model has so far mirrored all the characteristics or complications of diabetes in humans. Since this disease represents a chronic nutritional insult based on a diet bearing a high glycemic load, the ideal model should recapitulate the underlying dietary issues. Most rodent models have three shortcomings: (1) they are genetically or chemically modified to produce diabetes; (2) unlike humans, most require high-fat feeding; (3) and they take too long to develop diabetes. By contrast, Nile rats develop diabetes rapidly (8-10 weeks) with high-carbohydrate (hiCHO) diets, similar to humans, and are protected by high fat (with low glycemic load) intake. This review describes diabetes progression in the Nile rat, including various aspects of breeding, feeding, and handling for best experimental outcomes. The diabetes is characterized by a striking genetic permissiveness influencing hyperphagia and hyperinsulinemia; random blood glucose is the best index of disease progression; and kidney failure with chronic morbidity and death are outcomes, all of which mimic uncontrolled T2DM in humans. Non-alcoholic fatty liver disease (NAFLD), also described in diabetic humans, results from hepatic triglyceride and cholesterol accumulation associated with rising blood glucose. Protection is afforded by low glycemic load diets rich in certain fibers or polyphenols. Accordingly, the Nile rat provides a unique opportunity to identify the nutritional factors and underlying genetic and molecular mechanisms that characterize human T2DM.

Impact of high-fat, low-carbohydrate diet on myocardial substrate oxidation, insulin sensitivity, and cardiac function after ischemia-reperfusion

High-fat, low-carbohydrate Diet (HFLCD) impairs the myocardial response to ischemia-reperfusion, but the underlying mechanisms remain elusive. We sought to determine the magnitude of diet-induced alterations in intrinsic properties of the myocardium (including insulin sensitivity and substrate oxidation) and circulating substrate and insulin differences resulting from diet, leading to this impaired response. Rats were fed HFLCD (60% kcal from fat/30% protein/10% carbohydrate) or control diet (CONT) (16%/19%/65%) for 2 wk. Isolated hearts underwent global low-flow ischemia followed by reperfusion (I/R). Carbon-13 NMR spectroscopy was used to determine myocardial substrate TCA cycle entry. Myocardial insulin sensitivity was assessed as dose-response of Akt phosphorylation. There was a significant effect of HFLCD and I/R with both these factors leading to an increase in free fatty acid (FFA) oxidation and a decrease in carbohydrate or ketone oxidation. Following I/R, HFLCD led to decreased ketone and increased FFA oxidation; the recovery of left ventricular (LV) function was decreased in HFLCD and was negatively correlated with FFA oxidation and positively associated with ketone oxidation. HFLCD also resulted in reduced insulin sensitivity. Under physiologic ranges, there were no direct effects of buffer insulin and ketone levels on oxidation of any substrate and recovery of cardiac function after I/R. An insulin-ketone interaction exists for myocardial substrate oxidation characteristics. We conclude that the impaired recovery of function after ischemia-reperfusion with HFLCD is largely due to intrinsic diet effects on myocardial properties, rather than to diet effect on circulating insulin or substrate levels.

The comparison of serum vaspin and visfatin concentrations in obese and normal weight women

BACKGROUND AND OBJECTIVES

There is evidence based studies which show that plasma level of visfatin and vaspin in patients with type 2 diabetes mellitus elevate in comparison with healthy people. But there is no consistency in plasma visfatin and vaspin concentration between studies done on obese people. For this reason, the aim of this study is to investigate the serum level concentrations of visfatin and vaspin in obese women compared to normal weight women.

MATERIALS AND METHODS

The participants of this study consist of 43 women aged 20-50, and 43 healthy women with normal weight as a control group. They were matched for age and physical activity. 24h food recall was used to collect dietary information from subjects. Moreover, blood sampling was taken to measure the blood levels of sugar, lipid profile, vaspin and visfatin.

RESULTS

The mean serum level of visfatin was not statistically different between obese and normal weight women. But, the obese women had statistically higher mean serum level of vaspin than normal women (p=0.04). We found no relations between serum levels of vaspin with serum concentration of visfatin. Also, serum levels of these two adipokines were not related to the serum concentrations of fasting glucose, total cholesterol, low-density lipoprotein cholesterol and triglyserides and high-density lipoprotein cholesterol. Also, there was a significant positive relationship between carbohydrate intake and serum visfatin level in women participating to this study (p=0.018, r=0.257).

CONCLUSION

The results of this study demonstrated that the level of serum vaspin was significantly higher in obese women. But there were no differences in serum levels of visfatin in comparison to normal weight women. Meanwhile this study demonstrated a positive relationship between serum levels of visfatin with dietary intake of carbohydrate, but no relationship between serum level of visfatin and vaspin in women participating in this study.

Leptin resistance and diet-induced obesity: central and peripheral actions of leptin

Obesity is a chronic disease that represents one of the most serious global health burdens associated to an excess of body fat resulting from an imbalance between energy intake and expenditure, which is regulated by environmental and genetic interactions. The adipose-derived hormone leptin acts via a specific receptor in the brain to regulate energy balance and body weight, although this protein can also elicit a myriad of actions in peripheral tissues. Obese individuals, rather than be leptin deficient, have in most cases, high levels of circulating leptin. The failure of these high levels to control body weight suggests the presence of a resistance process to the hormone that could be partly responsible of disturbances on body weight regulation. Furthermore, leptin resistance can impair physiological peripheral functions of leptin such as lipid and carbohydrate metabolism and nutrient intestinal utilization. The present document summarizes those findings regarding leptin resistance development and the role of this hormone in the development and maintenance of an obese state. Thus, we focused on the effect of the impaired leptin action on adipose tissue, liver, skeletal muscle and intestinal function and the accompanying relationships with diet-induced obesity. The involvement of some inflammatory mediators implicated in the development of obesity and their roles in leptin resistance development are also discussed.

Premature guinea pigs: a new paradigm to investigate the late-effects of preterm birth

Preterm birth is common and the associated short-term morbidity well described. The adult-onset consequences of preterm birth are less clear, but cardiovascular and metabolic health may be adversely affected. Although large animal models of preterm birth addressing important short-term issues exist, long-term studies are hampered by significant logistical constraints. Current small animal models of prematurity require terminal caesarean section of the mother; both caesarean birth and early maternal care modify offspring adult cardio-metabolic function. We describe a novel method for inducing preterm labour in guinea pigs. With support comparable to that received by moderately preterm human infants, preterm pups are viable. Growth trajectories between preterm and term-born pups differ significantly; between term equivalent age and weaning ex-preterm animals demonstrate increased weight and ponderal index. We believe this novel paradigm will significantly improve our ability to investigate the cardio-metabolic sequelae of preterm birth throughout the life course and into the second generation.

Cholesterol-induced inflammation and macrophage accumulation in adipose tissue is reduced by a low carbohydrate diet in guinea pigs

BACKGROUND/OBJECTIVES

The main objective of this study was to evaluate the effects of a high cholesterol (HC) dietary challenge on cholesterol tissue accumulation, inflammation, adipocyte differentiation, and macrophage infiltration in guinea pigs. A second objective was to assess whether macronutrient manipulation would reverse these metabolic alterations.

MATERIALS/METHODS

Male Hartley guinea pigs (10/group) were assigned to either low cholesterol (LC) (0.04g/100g) or high cholesterol (HC) (0.25g/100g) diets for six weeks. For the second experiment, 20 guinea pigs were fed the HC diet for six weeks and then assigned to either a low carbohydrate (CHO) diet (L-CHO) (10% energy from CHO) or a high CHO diet (H-CHO) (54% CHO) for an additional six weeks.

RESULTS

Higher concentrations of total (P < 0.005) and free (P < 0.05) cholesterol were observed in both adipose tissue and aortas of guinea pigs fed the HC compared to those in the LC group. In addition, higher concentrations of pro-inflammatory cytokines in the adipose tissue (P < 0.005) and lower concentrations of anti-inflammatory interleukin (IL)-10 were observed in the HC group (P < 0.05) compared to the LC group. Of particular interest, adipocytes in the HC group were smaller in size (P < 0.05) and showed increased macrophage infiltration compared to the LC group. When compared to the H-CHO group, lower concentrations of cholesterol in both adipose and aortas as well as lower concentrations of inflammatory cytokines in adipose tissue were observed in the L-CHO group (P < 0.05). In addition, guinea pigs fed the L-CHO exhibited larger adipose cells and lower macrophage infiltration compared to the H-CHO group.

CONCLUSIONS

The results of this study strongly suggest that HC induces metabolic dysregulation associated with inflammation in adipose tissue and that L-CHO is more effective than H-CHO in attenuating these detrimental effects.

Hormonal appetite control is altered by shift work: a preliminary study

Shift work has been associated with a higher propensity for developing nutritional problems and obesity. However, the possible changes in leptin and ghrelin (2 hormones that contribute importantly to the central regulation of food intake) concentrations in this population are poorly described. The objective of the study was to evaluate the daily concentrations of leptin, nonacylated ghrelin, and acylated ghrelin and the appetite ratings in men working different shift schedules. Daily concentrations of nonacylated ghrelin, acylated ghrelin, and leptin and appetite were measured in 3 groups of subjects: workers on fixed night shifts (n = 9), fixed early morning shifts (n = 6), and fixed day shifts (n = 7). Appetite was evaluated by a validated questionnaire. Blood samples were collected every 4 hours over the course of 24 hours for a total of 6 samples. When comparing the 3 groups, leptin concentrations at 8:00 am and 4:00 pm for those workers on the day shift were significantly lower than for those on the early morning shift; and concentrations at noon for those workers on the day shift were significantly lower than for those on the night shift. Nonacylated and acylated ghrelin concentrations were significantly lower for those workers on the early morning shift than for those on the day shift. In general, appetite was the lowest in those working the early morning shift. Shift workers on the early morning shift have lower appetites and concentrations of leptin and nonacylated and acylated ghrelin than the workers on other shifts. Further studies are required to better understand the detailed needs of these individuals.

Suppression of FoxO1 activity by long-chain fatty acyl analogs

OBJECTIVE

Overactivity of the Forkhead transcription factor FoxO1 promotes diabetic hyperglycemia, dyslipidemia, and acute-phase response, whereas suppression of FoxO1 activity by insulin may alleviate diabetes. The reported efficacy of long-chain fatty acyl (LCFA) analogs of the MEDICA series in activating AMP-activated protein kinase (AMPK) and in treating animal models of diabesity may indicate suppression of FoxO1 activity.

RESEARCH DESIGN AND METHODS

The insulin-sensitizing and anti-inflammatory efficacy of a MEDICA analog has been verified in guinea pig and in human C-reactive protein (hCRP) transgenic mice, respectively. Suppression of FoxO1 transcriptional activity has been verified in the context of FoxO1- and STAT3-responsive genes and compared with suppression of FoxO1 activity by insulin and metformin.

RESULTS

Treatment with MEDICA analog resulted in total body sensitization to insulin, suppression of lipopolysaccharide-induced hCRP and interleukin-6-induced acute phase reactants and robust decrease in FoxO1 transcriptional activity and in coactivation of STAT3. Suppression of FoxO1 activity was accounted for by its nuclear export by MEDICA-activated AMPK, complemented by inhibition of nuclear FoxO1 transcriptional activity by MEDICA-induced C/EBPβ isoforms. Similarly, insulin treatment resulted in nuclear exclusion of FoxO1 and further suppression of its nuclear activity by insulin-induced C/EBPβ isoforms. In contrast, FoxO1 suppression by metformin was essentially accounted for by its nuclear export by metformin-activated AMPK.

CONCLUSIONS

Suppression of FoxO1 activity by MEDICA analogs may partly account for their antidiabetic anti-inflammatory efficacy. FoxO1 suppression by LCFA analogs may provide a molecular rational for the beneficial efficacy of carbohydrate-restricted ketogenic diets in treating diabetes.

Low-carbohydrate diets and prostate cancer: how low is "low enough"?

Previous studies indicate that carbohydrate intake influences prostate cancer biology, as mice fed a no-carbohydrate ketogenic diet (NCKD) had significantly smaller xenograft tumors and longer survival than mice fed a Western diet. As it is nearly impossible for humans to consume and maintain NCKD, we determined whether diets containing 10% or 20% carbohydrate kcal showed similar tumor growth as NCKD. A total of 150 male severe combined immunodeficient mice were fed a Western diet ad libitum, injected with the human prostate cancer cell line LAPC-4, and then randomized 2 weeks later to one of three arms: NCKD, 10% carbohydrate, or 20% carbohydrate diets. Ten mice not injected were fed an ad libitum low-fat diet (12% fat kcal) serving as the reference in a modified-paired feeding protocol. Mice were sacrificed when tumors reached 1,000 mm(3). Despite consuming extra calories, all mice receiving low-carbohydrate diets were significantly lighter than those receiving a low-fat diet (P < 0.04). Among the low-carbohydrate arms, NCKD-fed mice were significantly lighter than the 10% or 20% carbohydrate groups (P < 0.05). Tumors were significantly larger in the 10% carbohydrate group on days 52 and 59 (P < 0.05), but at no other point during the study. Diet did not affect survival (P = 0.34). There were no differences in serum insulin-like growth factor-I or insulin-like growth factor binding protein-3 at sacrifice among the low-carbohydrate arms (P = 0.07 and P = 0.55, respectively). Insulin was significantly lower in the 20% carbohydrate arm (P = 0.03). LAPC-4 xenograft mice fed a low-carbohydrate diet (10-20% carbohydrate kcal) had similar survival as mice consuming NCKD (0% carbohydrate kcal).