Low-carbohydrate high-fat diets in combination with daily exercise in rats: Effects on body weight regulation, body composition and exercise capacity

Phycocyanin attenuates skeletal muscle damage and fatigue via modulation of Nrf2 and IRS-1/AKT/mTOR pathway in exercise-induced oxidative stress in rats

Prolonged strenuous exercise induces oxidative stress, leading to oxidative damage, skeletal muscle fatigue, and reduced exercise performance. The body compensates for oxidative stress through antioxidant actions, while related enzymes alone may not overcome excessive oxidative stress during prolonged strenuous exercise. Phycocyanin is an important antioxidant supplement derived from blue-green algae, which may be helpful in this type of situation. This study determined the effects of phycocyanin on exercise performance from prolonged strenuous exercise. Forty Sprague Dawley male rats were divided into 5 groups (n = 8 /group); Control group (C), Exercise group (E), and Exercise with supplement groups receiving low dose (Phycocyanin = 100 mg/kg BW; ELP) and high dose (Phycocyanin = 200 mg/kg BW; EHP) or vitamin C (Vitamin C = 200 mg/kg BW; VC). Phycocyanin was found to decrease oxidative damage markers, muscle fatigue, and muscle atrophy through the activated AKT/mTOR pathway. This was also found to have greater increases in antioxidants via Nrf2 signaling and increases ATP synthesis, GLUT4 transporters, and insulin signaling due to increased IRS-1/AKT signaling. In conclusion, phycocyanin was found to reduce oxidative damage and muscle atrophy, including an increase in insulin signaling in skeletal muscles leading to increased exercise performance in rats.

Ketogenic diets, physical activity and body composition: a review

Obesity remains a serious relevant public health concern throughout the world despite related countermeasures being well understood (i.e. mainly physical activity and an adjusted diet). Among different nutritional approaches, there is a growing interest in ketogenic diets (KD) to manipulate body mass (BM) and to enhance fat mass loss. KD reduce the daily amount of carbohydrate intake drastically. This results in increased fatty acid utilisation, leading to an increase in blood ketone bodies (acetoacetate, 3-β-hydroxybutyrate and acetone) and therefore metabolic ketosis. For many years, nutritional intervention studies have focused on reducing dietary fat with little or conflicting positive results over the long term. Moreover, current nutritional guidelines for athletes propose carbohydrate-based diets to augment muscular adaptations. This review discusses the physiological basis of KD and their effects on BM reduction and body composition improvements in sedentary individuals combined with different types of exercise (resistance training or endurance training) in individuals with obesity and athletes. Ultimately, we discuss the strengths and the weaknesses of these nutritional interventions together with precautionary measures that should be observed in both individuals with obesity and athletic populations. A literature search from 1921 to April 2021 using Medline, Google Scholar, PubMed, Web of Science, Scopus and Sportdiscus Databases was used to identify relevant studies. In summary, based on the current evidence, KD are an efficient method to reduce BM and body fat in both individuals with obesity and athletes. However, these positive impacts are mainly because of the appetite suppressive effects of KD, which can decrease daily energy intake. Therefore, KD do not have any superior benefits to non-KD in BM and body fat loss in individuals with obesity and athletic populations in an isoenergetic situation. In sedentary individuals with obesity, it seems that fat-free mass (FFM) changes appear to be as great, if not greater, than decreases following a low-fat diet. In terms of lean mass, it seems that following a KD can cause FFM loss in resistance-trained individuals. In contrast, the FFM-preserving effects of KD are more efficient in endurance-trained compared with resistance-trained individuals.

Isonitrogenous low-carbohydrate diet elicits specific changes in metabolic gene expression in the skeletal muscle of exercise-trained mice

With the renewed interest in low-carbohydrate diets (LCDs) in the sports field, a few animal studies have investigated their potential. However, most rodent studies have used an LCD containing low protein, which does not recapitulate a human LCD, and the muscle-specific adaptation in response to an LCD remains unclear. Therefore, we investigated the effects of two types of LCDs, both containing the same proportion of protein as a regular diet (isonitrogenous LCD; INLCD), on body composition, exercise performance, and metabolic fuel selection at the genetic level in the skeletal muscles of exercise-trained mice. Three groups of mice (n = 8 in each group), one fed a regular AIN-93G diet served as the control, and the others fed either of the two INLCDs containing 20% protein and 10% carbohydrate (INLCD-10%) or 20% protein and 1% carbohydrate (INLCD-1%) had a regular exercise load (5 times/week) for 12 weeks. Body weight and muscle mass did not decrease in either of the INLCD-fed groups, and the muscle glycogen levels and endurance capacity did not differ among the three groups. Only in the mice fed INLCD-1% did the plasma ketone concentration significantly increase, and gene expression related to glucose utilization significantly declined in the muscles. Both INLCD-1% and INLCD-10% consumption increased gene expression related to lipid utilization. These results suggest that, although INLCD treatment did not affect endurance capacity, it helped maintain muscle mass and glycogen content regardless of the glucose intake restrictions in trained mice. Moreover, an INLCD containing a low carbohydrate content might present an advantage by increasing lipid oxidation without ketosis and suppressing muscle glucose utilization.

Sex-dependent effects of forced exercise in the body composition of adolescent rats

Determining the body composition during adolescence can predict diseases such as obesity, diabetes, and metabolic syndromes later in life; and physical activity became an effective way to restore changes in body composition. However, current available literature assessing the body composition before, during and after adolescence in female and male rodents by in vivo techniques is scarce. Thus, by using computerized tomography, we aimed to define the baseline of the weight and body composition during the adolescence and young adulthood of female and male Sprague-Dawley rats (on P30, P60 and P90) under standard diet. Then, we determined the effect of 18 days of forced exercise on the body weight and composition during the early adolescence (P27-45). The highest percentual increments in weight, body volume and relative adipose contents occurred during the female and male adolescence. Forced running during the early adolescence decreased weight, body volume and relative adipose delta and increment values in males only. The adolescence of rats is a period of drastic body composition changes, where exercise interventions have sex-dependent effects. These results support a model that could open new research windows in the field of adolescent obesity.

A Handful of Details to Ensure the Experimental Reproducibility on the FORCED Running Wheel in Rodents: A Systematic Review

A well-documented method and experimental design are essential to ensure the reproducibility and reliability in animal research. Experimental studies using exercise programs in animal models have experienced an exponential increase in the last decades. Complete reporting of forced wheel and treadmill exercise protocols would help to ensure the reproducibility of training programs. However, forced exercise programs are characterized by a poorly detailed methodology. Also, current guidelines do not cover the minimum data that must be included in published works to reproduce training programs. For this reason, we have carried out a systematic review to determine the reproducibility of training programs and experimental designs of published research in rodents using a forced wheel system. Having determined that most of the studies were not detailed enough to be reproducible, we have suggested guidelines for animal research using FORCED exercise wheels, which could also be applicable to any form of forced exercise.

Dietary Approaches to Cancer Therapy

The concept that dietary changes could improve the response to cancer therapy is extremely attractive to many patients, who are highly motivated to take control of at least some aspect of their treatment. Growing insight into cancer metabolism is highlighting the importance of nutrient supply to tumor development and therapeutic response. Cancers show diverse metabolic requirements, influenced by factors such as tissue of origin, microenvironment, and genetics. Dietary modulation will therefore need to be matched to the specific characteristics of both cancers and treatment, a precision approach requiring a detailed understanding of the mechanisms that determine the metabolic vulnerabilities of each cancer.

The carbohydrate-insulin model does not explain the impact of varying dietary macronutrients on the body weight and adiposity of mice

Objectives

The carbohydrate-insulin model (CIM) predicts that increases in fasting and post-prandial insulin in response to dietary carbohydrates stimulate energy intake and lower energy expenditures, leading to positive energy balance and weight gain. The objective of the present study was to directly test the CIM's predictions using C57BL/6 mice.

Methods

Diets were designed by altering dietary carbohydrates with either fixed protein or fat content and were fed to C57BL/6 mice acutely or chronically for 12 weeks. The body weight, body composition, food intake, and energy expenditures of the mice were measured. Their fasting and post-prandial glucose and insulin levels were also measured. RNA-seq was performed on RNA from the hypothalamus and subcutaneous white adipose tissue. Pathway analysis was conducted using IPA.

Results

Only the post-prandial insulin and fasting glucose levels followed the CIM's predictions. The lipolysis and leptin signaling pathways in the sWAT were inhibited in relation to the elevated fasting insulin, supporting the CIM's predicted impact of high insulin. However, because higher fasting insulin was unrelated to carbohydrate intake, the overall pattern did not support the model. Moreover, the hypothalamic hunger pathways were inhibited in relation to the increased fasting insulin, and the energy intake was not increased. The browning pathway in the sWAT was inhibited at higher insulin levels, but the daily energy expenditure was not altered.

Conclusions

Two of the predictions were partially supported (and hence also partially not supported) and the other three predictions were not supported. We conclude that the CIM does not explain the impact of dietary macronutrients on adiposity in mice.

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Higher fasting insulin related to inhibited lipolysis and leptin pathways in sWAT, supporting CIM.

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Higher fasting insulin related to inhibited hypothalamic hunger pathway, contrasting CIM.

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Fasting insulin decreased with higher dietary carbohydrate, overall contrasting CIM.

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Higher dietary carbohydrate did not lead to greater EI/adiposity, or lowered EE.

Dietary Fiber in Bilberry Ameliorates Pre-Obesity Events in Rats by Regulating Lipid Depot, Cecal Short-Chain Fatty Acid Formation and Microbiota Composition

Obesity is linked to non-alcoholic fatty liver disease and risk factors associated to metabolic syndrome. Bilberry (Vaccinium myrtillus) that contains easily fermentable fiber may strengthen the intestinal barrier function, attenuate inflammation and modulate gut microbiota composition, thereby prevent obesity development. In the current study, liver lipid metabolism, fat depot, cecal and serum short-chain fatty acids (SCFAs) and gut microbiome were evaluated in rats fed bilberries in a high-fat (HFD + BB) or low-fat (LFD + BB) setting for 8 weeks and compared with diets containing equal amount of fiber resistant to fermentation (cellulose, HFD and LFD). HFD fed rats did not obtain an obese phenotype but underwent pre-obesity events including increased liver index, lipid accumulation and increased serum cholesterol levels. This was linked to shifts of cecal bacterial community and reduction of major SCFAs. Bilberry inclusion improved liver metabolism and serum lipid levels. Bilberry inclusion under either LFD or HFD, maintained microbiota homeostasis, stimulated interscapular-brown adipose tissue depot associated with increased mRNA expression of uncoupling protein-1; enhanced SCFAs in the cecum and circulation; and promoted butyric acid and butyrate-producing bacteria. These findings suggest that bilberry may serve as a preventative dietary measure to optimize microbiome and associated lipid metabolism during or prior to HFD.

Benefits of resistance training on body composition and glucose clearance are inhibited by long-term low carbohydrate diet in rats

Background/Objectives

Regular exercise training is effective to altering many markers of metabolic syndrome and its effects are strongly influenced by the type of consumed diet. Nowadays, resistance training (RT) has been frequently associated with low-carbohydrate high-fat diet (LCD). After long term these diets causes body weight (BW) regain with deleterious effects on body composition and metabolic risk factors. The effects of RT associated with long-term LCD on these parameters remain unexplored. We aimed to investigate the effects of RT when associated with long-term LCD on BW, feed efficiency, body composition, glucose homeostasis, liver parameters and serum biochemical parameters during BW regain period in rats.

Subjects/Methods

Male Sprague–Dawley rats were fed with LCD (LC groups) or standard diet (STD) (ST groups). After 10 weeks-diet animals were separated into sedentary (Sed-LC and Sed-ST) and resistance-trained (RT-LC and RT-ST) groups (N = 8/group). RT groups performed an 11-week climbing program on a ladder with progressive load. Dual x-ray absorptiometry, glucose tolerance tests and insulin tolerance tests were performed at weeks 10 and 20. Liver and serum were collected at week 21.

Results

RT reduced feed efficiency, BW gain, liver fat and total and LDL cholesterol, and improved body composition and glucose clearance in animals fed on STD. In those fed with LCD, RT reduced caloric intake, BW regain, liver fat and serum triglycerides levels. However, improvement in body composition was inhibited and bone mineral density and glucose clearance was further impaired in this association.

Conclusions

The LCD nullifies the beneficial effects of RT on body composition, glucose homeostasis and impairs some health parameters. Our results do not support the association of RT with LCD in a long term period.

Evaluation of efforts in untrained Wistar rats following exercise on forced running wheel at maximal lactate steady state

[Purpose]

We aimed to examine the effect of running speed on metabolic responses associated with maximal lactate steady state (MLSS) in rats during forced running wheel (FRW) exercise.

[Methods]

Forty male adult Wistar rats were divided into seven groups. The blood lactate threshold and peak running speed were determined for an incremental power test group. Five groups participated in constant power tests at intensities 10, 13, 14.5, 16, and 17.5 m/min to determine MLSS and a non-exercise group was chosen as the control. Animals were euthanized immediately after constant power tests and their corticosterone, non-esterified fatty acid (NEFA), blood glucose, and creatine kinase (CK) levels analyzed. The differences among groups were identified by one-way analysis of variance (p < 0.05).

[Results]

Blood lactate threshold corresponded a running intensity of 15 m/min, while MLSS was determined to be 16 m/min. Serum corticosterone concentrations were significantly higher in 14.5, 16, and 17.5 m/min groups (298.8±62, 338.3±65, and 354±26 nM, respectively) as compared to that in the control group (210.6±16 nM). Concentrations of NEFA observed in groups 13, 14.5, 16, and 17.5 m/min (662.8±24, 702.35±69, 718.4±34, and 752.8±77 μM, respectively) were significantly higher than those in 10 m/min and control groups (511.1±53 and 412.1±56 μM, respectively). The serum CK concentration recorded for group 17.5 m/min (372.4±56 U/L) was higher than those recorded for other groups.

[Conclusion]

The speed above 16 m/min on FRW resulted in increased physiological demands and muscle damage in untrained healthy Wistar rats.

Habituation Training Improves Locomotor Performance in a Forced Running Wheel System in Rats

Increasing evidence supports that physical activity promotes mental health; and regular exercise may confer positive effects in neurological disorders. There is growing number of reports that requires the analysis of the impact of physical activity in animal models. Exercise in rodents can be performed under voluntary or forced conditions. The former presents the disadvantage that the volume and intensity of exercise varies from subject to subject. On the other hand, a major challenge of the forced training protocol is the low level of performance typically achieved within a given session. Thus, the aim of the present study was to evaluate the effectiveness of gradual increasing of the volume and intensity (training habituation protocol) to improve the locomotor performance in a forced running-wheel system in rats. Sprague-Dawley rats were randomly assigned to either a group that received an exercise training habituation protocol, or a control group. The locomotor performance during forced running was assessed by an incremental exercise test. The experimental results reveal that the total running time and the distance covered by habituated rats was significantly higher than in control ones. We conclude that the exercise habituation protocol improves the locomotor performance in forced running wheels.

An Innovative Running Wheel-based Mechanism for Improved Rat Training Performance

This study presents an animal mobility system, equipped with a positioning running wheel (PRW), as a way to quantify the efficacy of an exercise activity for reducing the severity of the effects of the stroke in rats. This system provides more effective animal exercise training than commercially available systems such as treadmills and motorized running wheels (MRWs). In contrast to an MRW that can only achieve speeds below 20 m/min, rats are permitted to run at a stable speed of 30 m/min on a more spacious and high-density rubber running track supported by a 15 cm wide acrylic wheel with a diameter of 55 cm in this work. Using a predefined adaptive acceleration curve, the system not only reduces the operator error but also trains the rats to run persistently until a specified intensity is reached. As a way to evaluate the exercise effectiveness, real-time position of a rat is detected by four pairs of infrared sensors deployed on the running wheel. Once an adaptive acceleration curve is initiated using a microcontroller, the data obtained by the infrared sensors are automatically recorded and analyzed in a computer. For comparison purposes, 3 week training is conducted on rats using a treadmill, an MRW and a PRW. After surgically inducing middle cerebral artery occlusion (MCAo), modified neurological severity scores (mNSS) and an inclined plane test were conducted to assess the neurological damages to the rats. PRW is experimentally validated as the most effective among such animal mobility systems. Furthermore, an exercise effectiveness measure, based on rat position analysis, showed that there is a high negative correlation between the effective exercise and the infarct volume, and can be employed to quantify a rat training in any type of brain damage reduction experiments.

A 3-day high-fat/low-carbohydrate diet does not alter exercise-induced growth hormone response in healthy males

OBJECTIVE

The purpose of the present study was to examine the effects of 3 days isoenergetic high-fat/low-carbohydrate diet (HF-LC) relative to low-fat/high-carbohydrate diet (LF-HC) on the exercise-induced growth hormone (GH) response in healthy male subjects.

DESIGN

Ten healthy young males participated in this study. Each subject consumed the HF-LC (18±1% protein, 61±2% fat, 21±1% carbohydrate, 2720 kcal per day) for 3 consecutive days after consuming the LF-HC (18±1% protein, 20±1% fat, 62±1% carbohydrate, 2755 kcal per day) for 3 consecutive days. After each dietary intervention period, the hormonal and metabolic responses to an acute exercise (30 min of continuous pedaling at 60% of V˙O2max) were compared. The intramyocellular lipid (IMCL) contents in the vastus lateralis, soleus, and tibialis anterior were evaluated by proton magnetic resonance spectroscopy.

RESULTS

Serum GH concentrations increased significantly during the exercise after both the HF-LC and LF-HC periods (P<0.05). However, the exercise-induced GH response was not significantly different between the two periods. Fat utilization and lipolytic responses during the exercise were enhanced significantly after the HF-LC period compared with the LF-HC period. IMCL content did not differ significantly in any portion of muscle after the dietary interventions.

CONCLUSIONS

We could not show that short-term HF-LC consumption changed significantly exercise-induced GH response or IMCL content in healthy young males.

Low-carbohydrate, high-fat diets have sex-specific effects on bone health in rats

PURPOSE

Studies in humans suggest that consumption of low-carbohydrate, high-fat diets (LC-HF) could be detrimental for growth and bone health. In young male rats, LC-HF diets negatively affect bone health by impairing the growth hormone/insulin-like growth factor axis (GH/IGF axis), while the effects in female rats remain unknown. Therefore, we investigated whether sex-specific effects of LC-HF diets on bone health exist.

METHODS

Twelve-week-old male and female Wistar rats were isoenergetically pair-fed either a control diet (CD), "Atkins-style" protein-matched diet (LC-HF-1), or ketogenic low-protein diet (LC-HF-2) for 4 weeks. In females, microcomputed tomography and histomorphometry analyses were performed on the distal femur. Sex hormones were analysed with liquid chromatography-tandem mass spectrometry, and endocrine parameters including GH and IGF-I were measured by immunoassay.

RESULTS

Trabecular bone volume, serum IGF-I and the bone formation marker P1NP were lower in male rats fed both LC-HF diets versus CD. LC-HF diets did not impair bone health in female rats, with no change in trabecular or cortical bone volume nor in serum markers of bone turnover between CD versus both LC-HF diet groups. Pituitary GH secretion was lower in female rats fed LC-HF diet, with no difference in circulating IGF-I. Circulating sex hormone concentrations remained unchanged in male and female rats fed LC-HF diets.

CONCLUSION

A 4-week consumption of LC-HF diets has sex-specific effects on bone health-with no effects in adult female rats yet negative effects in adult male rats. This response seems to be driven by a sex-specific effect of LC-HF diets on the GH/IGF system.

Improved infrared-sensing running wheel systems with an effective exercise activity indicator

This paper describes an infrared-sensing running wheel (ISRW) system for the quantitative measurement of effective exercise activity in rats. The ISRW system provides superior exercise training compared with commercially available traditional animal running platforms. Four infrared (IR) light-emitting diode/detector pairs embedded around the rim of the wheel detect the rat's real-time position; the acrylic wheel has a diameter of 55 cm and a thickness of 15 cm, that is, it is larger and thicker than traditional exercise wheels, and it is equipped with a rubber track. The acrylic wheel hangs virtually frictionless, and a DC motor with an axially mounted rubber wheel, which has a diameter of 10 cm, drives the acrylic wheel from the outer edge. The system can automatically train rats to run persistently. The proposed system can determine effective exercise activity (EEA), with the IR sensors (which are connected to a conventional PC) recording the rat exercise behavior. A prototype of the system was verified by a hospital research group performing ischemic stroke experiments on rats by considering middle cerebral artery occlusion. The experimental data demonstrated that the proposed system provides greater neuroprotection in an animal stroke model compared with a conventional treadmill and a motorized running wheel for a given exercise intensity. The quantitative exercise effectiveness indicator showed a 92% correlation between an increase in the EEA and a decrease in the infarct volume. This indicator can be used as a noninvasive and objective reference in clinical animal exercise experiments.

A forced running wheel system with a microcontroller that provides high-intensity exercise training in an animal ischemic stroke model

We developed a forced non-electric-shock running wheel (FNESRW) system that provides rats with high-intensity exercise training using automatic exercise training patterns that are controlled by a microcontroller. The proposed system successfully makes a breakthrough in the traditional motorized running wheel to allow rats to perform high-intensity training and to enable comparisons with the treadmill at the same exercise intensity without any electric shock. A polyvinyl chloride runway with a rough rubber surface was coated on the periphery of the wheel so as to permit automatic acceleration training, and which allowed the rats to run consistently at high speeds (30 m/min for 1 h). An animal ischemic stroke model was used to validate the proposed system. FNESRW, treadmill, control, and sham groups were studied. The FNESRW and treadmill groups underwent 3 weeks of endurance running training. After 3 weeks, the experiments of middle cerebral artery occlusion, the modified neurological severity score (mNSS), an inclined plane test, and triphenyltetrazolium chloride were performed to evaluate the effectiveness of the proposed platform. The proposed platform showed that enhancement of motor function, mNSS, and infarct volumes was significantly stronger in the FNESRW group than the control group (P<0.05) and similar to the treadmill group. The experimental data demonstrated that the proposed platform can be applied to test the benefit of exercise-preconditioning-induced neuroprotection using the animal stroke model. Additional advantages of the FNESRW system include stand-alone capability, independence of subjective human adjustment, and ease of use.

Long-term ketogenic diet causes glucose intolerance and reduced β- and α-cell mass but no weight loss in mice

High-fat, low-carbohydrate ketogenic diets (KD) are used for weight loss and for treatment of refractory epilepsy. Recently, short-time studies in rodents have shown that, besides their beneficial effect on body weight, KD lead to glucose intolerance and insulin resistance. However, the long-term effects on pancreatic endocrine cells are unknown. In this study we investigate the effects of long-term KD on glucose tolerance and β- and α-cell mass in mice. Despite an initial weight loss, KD did not result in weight loss after 22 wk. Plasma markers associated with dyslipidemia and inflammation (cholesterol, triglycerides, leptin, monocyte chemotactic protein-1, IL-1β, and IL-6) were increased, and KD-fed mice showed signs of hepatic steatosis after 22 wk of diet. Long-term KD resulted in glucose intolerance that was associated with insufficient insulin secretion from β-cells. After 22 wk, insulin-stimulated glucose uptake was reduced. A reduction in β-cell mass was observed in KD-fed mice together with an increased number of smaller islets. Also α-cell mass was markedly decreased, resulting in a lower α- to β-cell ratio. Our data show that long-term KD causes dyslipidemia, a proinflammatory state, signs of hepatic steatosis, glucose intolerance, and a reduction in β- and α-cell mass, but no weight loss. This indicates that long-term high-fat, low-carbohydrate KD lead to features that are also associated with the metabolic syndrome and an increased risk for type 2 diabetes in humans.

Impaired glucose tolerance in rats fed low-carbohydrate, high-fat diets

Moderate low-carbohydrate/high-fat (LC-HF) diets are widely used to induce weight loss in overweight subjects, whereas extreme ketogenic LC-HF diets are used to treat neurological disorders like pediatric epilepsy. Usage of LC-HF diets for improvement of glucose metabolism is highly controversial; some studies suggest that LC-HF diets ameliorate glucose tolerance, whereas other investigations could not identify positive effects of these diets or reported impaired insulin sensitivity. Here, we investigate the effects of LC-HF diets on glucose and insulin metabolism in a well-characterized animal model. Male rats were fed isoenergetic or hypocaloric amounts of standard control diet, a high-protein "Atkins-style" LC-HF diet, or a low-protein, ketogenic, LC-HF diet. Both LC-HF diets induced lower fasting glucose and insulin levels associated with lower pancreatic β-cell volumes. However, dynamic challenge tests (oral and intraperitoneal glucose tolerance tests, insulin-tolerance tests, and hyperinsulinemic euglycemic clamps) revealed that LC-HF pair-fed rats exhibited impaired glucose tolerance and impaired hepatic and peripheral tissue insulin sensitivity, the latter potentially being mediated by elevated intramyocellular lipids. Adjusting visceral fat mass in LC-HF groups to that of controls by reducing the intake of LC-HF diets to 80% of the pair-fed groups did not prevent glucose intolerance. Taken together, these data show that lack of dietary carbohydrates leads to glucose intolerance and insulin resistance in rats despite causing a reduction in fasting glucose and insulin concentrations. Our results argue against a beneficial effect of LC-HF diets on glucose and insulin metabolism, at least under physiological conditions. Therefore, use of LC-HF diets for weight loss or other therapeutic purposes should be balanced against potentially harmful metabolic side effects.

High-fat, low-carbohydrate diet alters myocardial oxidative stress and impairs recovery of cardiac function after ischemia and reperfusion in obese rats

Obesity is associated with elevated risk of heart disease. A solid understanding of the safety and potential adverse effects of high-fat, low-carbohydrate diet (HFLCD) similar to that used by humans for weight loss on the heart is crucial. High fat intake is known to promote increases in reactive oxygen species and mitochondrial damage. We hypothesized that there would be adverse effects of HFLCD on myocardial ischemia/reperfusion injury through enhancing oxidative stress injury and impairing mitochondrial biogenesis in a nongenetic, diet-induced rat model of obesity. To test the hypothesis, 250-g male Sprague-Dawley rats were fed an obesity-promoting diet for 7 weeks to induce obesity, then switched to HFLCD or a low-fat control diet for 2 weeks. Isolated hearts underwent global low flow ischemia for 60 minutes and reperfusion for 60 minutes. High-fat, low-carbohydrate diet resulted in greater weight gain and lower myocardial glycogen, plasma adiponectin, and insulin. Myocardial antioxidant gene transcript and protein expression of superoxide dismutase and catalase were reduced in HFLCD, along with increased oxidative gene NADPH oxidase-4 transcript and xanthine oxidase activity, and a 37% increase in nitrated protein (nitrotyrosine) in HFLCD hearts. The cardiac expression of key mitochondrial regulatory factors such as nuclear respiratory factor-1 and transcription factor A-mitochondrial were inhibited and myocardial mitochondrial DNA copy number decreased. The cardiac expression of adiponectin and its receptors was down-regulated in HFLCD. High-fat, low-carbohydrate diet impaired recovery of left ventricular rate-pressure product after ischemia/reperfusion and led to 3.5-fold increased injury as measured by lactate dehydrogenase release. In conclusion, HFLCD leads to increased ischemic myocardial injury and impaired recovery of function after reperfusion and was associated with attenuation of mitochondrial biogenesis and enhanced oxidative stress in obese rats. These findings may have important implications for diet selection in obese patients with ischemic heart disease.