Adaptive reciprocity of lipid and glucose metabolism in human short-term starvation

Ketogenic low-CHO, high-fat diet: the future of elite endurance sport?

The ability of ketogenic low‐carbohydrate (CHO) high‐fat (K‐LCHF) diets to enhance muscle fat oxidation has led to claims that it is the ‘future of elite endurance sport’. There is robust evidence that substantial increases in fat oxidation occur, even in elite athletes, within 3–4 weeks and possibly 5–10 days of adherence to a K‐LCHF diet. Retooling of the muscle can double exercise fat use to ∼1.5 g min⁻¹, with the intensity of maximal rates of oxidation shifting from ∼45% to ∼70% of maximal aerobic capacity. Reciprocal reductions in CHO oxidation during exercise are clear, but current evidence to support the hypothesis of the normalization of muscle glycogen content with longer‐term adaptation is weak. Importantly, keto‐adaptation may impair the muscle's ability to use glycogen for oxidative fates, compromising the use of a more economical energy source when the oxygen supply becomes limiting and, thus, the performance of higher‐intensity exercise (>80% maximal aerobic capacity). Even with moderate intensity exercise, individual responsiveness to K‐LCHF is varied, with extremes at both ends of the performance spectrum. Periodisation of K‐LCHF with high CHO availability might offer opportunities to restore capacity for higher‐intensity exercise, but investigations of various models have failed to find a benefit over dietary approaches based on current sports nutrition guidelines. Endurance athletes who are contemplating the use of K‐LCHF should undertake an audit of event characteristics and personal experiences to balance the risk of impaired performance of higher‐intensity exercise with the likelihood of an unavoidable depletion of carbohydrate stores.

A Case of Hypoglycemia Associated With the Ketogenic Diet and Alcohol Use

The ketogenic diet, which has become an increasingly popular diet, severely restricts carbohydrate intake to shunt metabolism towards fatty acid oxidation and production of ketones as a fuel source. There have been many studies illustrating the positive effects of a ketogenic diet in weight loss and other benefits; however, the long-term effects and potential adverse events of a ketogenic diet have not been well studied or documented in literature. There are a few case reports of ketogenic diet resulting in hypoglycemia. We report a case of hypoglycemia with a blood glucose of 39 mg/dL and ketosis in a 69-year-old woman who strictly followed a ketogenic diet for nearly one year. She presented with malaise, sugar cravings, and mental fogginess, and after intake of alcoholic beverages, was admitted to the hospital with hypoglycemia. She had elevated beta-hydroxybutyrate, and low insulin and C-peptide, all consistent with a starvation ketosis. This case illustrates that adherence to a ketogenic diet for a prolonged period of time, in combination with alcohol intake, can disrupt normal glucose homeostatic mechanisms and result in a significant degree of hypoglycemia. This pattern of hypoglycemia may not present with classic symptoms, most likely partly due to effects of the ketogenic diet on brain function. This case provides insight that supports the need to counsel patients about alcohol intake while on the ketogenic diet. More information is needed on long-term complications of the ketogenic diet on glucose homeostasis in the body as well as in the brain.

Spatiotemporal gating of SIRT1 functions by O-GlcNAcylation is essential for liver metabolic switching and prevents hyperglycemia

Inefficient physiological transitions are known to cause metabolic disorders. Therefore, investigating mechanisms that constitute molecular switches in a central metabolic organ like the liver becomes crucial. Specifically, upstream mechanisms that control temporal engagement of transcription factors, which are essential to mediate physiological fed-fast-refed transitions are less understood. SIRT1, a NAD⁺-dependent deacetylase, is pivotal in regulating hepatic gene expression and has emerged as a key therapeutic target. Despite this, if/how nutrient inputs regulate SIRT1 interactions, stability, and therefore downstream functions are still unknown. Here, we establish nutrient-dependent O-GlcNAcylation of SIRT1, within its N-terminal domain, as a crucial determinant of hepatic functions. Our findings demonstrate that during a fasted-to-refed transition, glycosylation of SIRT1 modulates its interactions with various transcription factors and a nodal cytosolic kinase involved in insulin signaling. Moreover, sustained glycosylation in the fed state causes nuclear exclusion and cytosolic ubiquitin-mediated degradation of SIRT1. This mechanism exerts spatiotemporal control over SIRT1 functions by constituting a previously unknown molecular relay. Of note, loss of SIRT1 glycosylation discomposed these interactions resulting in aberrant gene expression, mitochondrial dysfunctions, and enhanced hepatic gluconeogenesis. Expression of nonglycosylatable SIRT1 in the liver abrogated metabolic flexibility, resulting in systemic insulin resistance, hyperglycemia, and hepatic inflammation, highlighting the physiological costs associated with its overactivation. Conversely, our study also reveals that hyperglycosylation of SIRT1 is associated with aging and high-fat-induced obesity. Thus, we establish that nutrient-dependent glycosylation of SIRT1 is essential to gate its functions and maintain physiological fitness.

The Effect of an 8 Week Prescribed Exercise and Low-Carbohydrate Diet on Cardiorespiratory Fitness, Body Composition and Cardiometabolic Risk Factors in Obese Individuals: A Randomised Controlled Trial

Background: Low-carbohydrate (LC) diets are an effective method for treating obesity and reducing cardiometabolic risk. However, exposure to LC diets is associated with reductions in muscle mass and increased osteoporosis risk in obese individuals. The combination of exercise with a LC diet appears to attenuate muscle mass loss induced by LC diets alone, and to further improve cardiometabolic profile. However, evidence to date in obese individuals is limited. We assessed the effect of LC diet in combination with supervised exercise on cardiorespiratory fitness, body composition and cardiometabolic risk factors in obese individuals. Methods: Male and female participants in the experimental (EX-LC; structured supervised exercise program + low-carbohydrate meals; n = 33; 35.3 years) and control (EX-CO; structured supervised exercise program + standard dietary advice; n = 31; 34.2 years) conditions underwent measurements of cardiorespiratory fitness (VO₂peak), body fat, lean muscle mass (LMM), and cardiometabolic biomarkers before and after an 8 week intervention. Results: Participants in the EX-LC condition demonstrated greater improvements in VO₂peak (p = 0.002) and fat mass index (FMI, p = 0.001) compared to the EX-CO condition. Achieving a ketogenic state (β-hydroxybutyrate, βHB ≥0.3 mmol/L) was associated with greater reductions in total body fat (p = 0.011), visceral adipose tissue (p = 0.025), FMI (p = 0.002) and C-reactive protein (CRP, p = 0.041) but also with greater reductions in LMM (p = 0.042). Conclusion: Short-term LC diet combined with prescribed exercise enhanced cardiorespiratory fitness and the cardiometabolic profile of obese individuals but was also associated with greater muscle mass loss compared to similar exercise training and standard dietary advice. The long-term effects of the LC diet should be further explored in future studies.

The Ghrelin-AgRP Neuron Nexus in Anorexia Nervosa: Implications for Metabolic and Behavioral Adaptations

Anorexia Nervosa (AN) is viewed as primarily a psychiatric disorder owing to the considerable behavioral and genetic overlap with mood disorders and other psychiatric traits. However, the recent reconceptualization of AN as one of both psychiatric and metabolic etiology suggests that metabolic circuits conveying hunger, or sensitive to signals of hunger, may be a critical nexus linking metabolic dysfunction to mood disturbances. Within the brain, hunger is primarily percieved by Agouti-related (AgRP) neurons and hunger increases plasma concentrations of the hormone ghrelin, which targets ghrelin receptors on AgRP neurons to facilitate metabolic adaptations to low energy availability. However, beyond the fundamental role in maintaining hunger signaling, AgRP neurons regulate a diverse range of behaviors such as motivation, locomotor activity, negative reinforcement, anxiety, and obsession and a key factor involved in the manifestation of these behavioral changes in response to activation is the presence or absence of food availability. These changes can be considered adaptive in that they promote affective food-seeking strategies in environments with limited food availability. However, it also suggests that these neurons, so well-studied for their metabolic control, shape mood-related behaviors in a context-dependent manner and dysfunctional control leads not only to metabolic problems but also potentially mood-related problems. The purpose of this review is to underline the potential role of AgRP neurons and ghrelin signaling in both the metabolic and behavioral changes observed in anorexia nervosa. We aim to highlight the most recent studies on AgRP neurons and ghrelin signaling and integrate their metabolic and behavioral roles in normal function and highlight how dysfunction may contribute to the development of AN.

Exercise Degrades Bone in Caloric Restriction, Despite Suppression of Marrow Adipose Tissue (MAT)

Marrow adipose tissue (MAT) and its relevance to skeletal health during caloric restriction (CR) is unknown: It remains unclear whether exercise, which is anabolic to bone in a calorie-replete state, alters bone or MAT in CR. We hypothesized that response of bone and MAT to exercise in CR differs from the calorie-replete state. Ten-week-old female B6 mice fed a regular diet (RD) or 30% CR diet were allocated to sedentary (RD, CR, n = 10/group) or running exercise (RD-E, CR-E, n = 7/group). After 6 weeks, CR mice weighed 20% less than RD, p < 0.001; exercise did not affect weight. Femoral bone volume (BV) via 3D MRI was 20% lower in CR versus RD (p < 0.0001). CR was associated with decreased bone by μCT: Tb.Th was 16% less in CR versus RD, p < 0.003, Ct.Th was 5% less, p < 0.07. In CR-E, Tb.Th was 40% less than RD-E, p < 0.0001. Exercise increased Tb.Th in RD (+23% RD-E versus RD, p < 0.003) but failed to do so in CR. Cortical porosity increased after exercise in CR (+28%, p = 0.04), suggesting exercise during CR is deleterious to bone. In terms of bone fat, metaphyseal MAT/ BV rose 159% in CR versus RD, p = 0.003 via 3D MRI. Exercise decreased MAT/BV by 52% in RD, p < 0.05, and also suppressed MAT in CR (-121%, p = 0.047). Histomorphometric analysis of adipocyte area correlated with MAT by MRI (R2 = 0.6233, p < 0.0001). With respect to bone, TRAP and Sost mRNA were reduced in CR. Intriguingly, the repressed Sost in CR rose with exercise and may underlie the failure of CR-bone quantity to increase in response to exercise. Notably, CD36, a marker of fatty acid uptake, rose 4088% in CR (p < 0.01 versus RD), suggesting that basal increases in MAT during calorie restriction serve to supply local energy needs and are depleted during exercise with a negative impact on bone. © 2019 The Authors. Journal of Bone and Mineral Research published by American Society for Bone and Mineral Research.

Human Postprandial Nutrient Metabolism and Low-Grade Inflammation: A Narrative Review

The importance of the postprandial state has been acknowledged, since hyperglycemia and hyperlipidemia are linked with several chronic systemic low-grade inflammation conditions. Humans spend more than 16 h per day in the postprandial state and the postprandial state is acknowledged as a complex interplay between nutrients, hormones and diet-derived metabolites. The purpose of this review is to provide insight into the physiology of the postprandial inflammatory response, the role of different nutrients, the pro-inflammatory effects of metabolic endotoxemia and the anti-inflammatory effects of bile acids. Moreover, we discuss nutritional strategies that may be linked to the described pathways to modulate the inflammatory component of the postprandial response.

Essentiality of fatty acid synthase in the 2D to anchorage-independent growth transition in transforming cells

Upregulation of fatty acid synthase (FASN) is a common event in cancer, although its mechanistic and potential therapeutic roles are not completely understood. In this study, we establish a key role of FASN during transformation. FASN is required for eliciting the anaplerotic shift of the Krebs cycle observed in cancer cells. However, its main role is to consume acetyl-CoA, which unlocks isocitrate dehydrogenase (IDH)-dependent reductive carboxylation, producing the reductive power necessary to quench reactive oxygen species (ROS) originated during the switch from two-dimensional (2D) to three-dimensional (3D) growth (a necessary hallmark of cancer). Upregulation of FASN elicits the 2D-to-3D switch; however, FASN's synthetic product palmitate is dispensable for this process since cells satisfy their fatty acid requirements from the media. In vivo, genetic deletion or pharmacologic inhibition of FASN before oncogenic activation prevents tumor development and invasive growth. These results render FASN as a potential target for cancer prevention studies.

Cachexia Anorexia Syndrome and Associated Metabolic Dysfunction in Peritoneal Metastasis

Patients with peritoneal metastasis (PM) of gastrointestinal and gynecological origin present with a nutritional deficit characterized by increased resting energy expenditure (REE), loss of muscle mass, and protein catabolism. Progression of peritoneal metastasis, as with other advanced malignancies, is associated with cancer cachexia anorexia syndrome (CAS), involving poor appetite (anorexia), involuntary weight loss, and chronic inflammation. Eventual causes of mortality include dysfunctional metabolism and energy store exhaustion. Etiology of CAS in PM patients is multifactorial including tumor growth, host response, cytokine release, systemic inflammation, proteolysis, lipolysis, malignant small bowel obstruction, ascites, and gastrointestinal side effects of drug therapy (chemotherapy, opioids). Metabolic changes of CAS in PM relate more to a systemic inflammatory response than an adaptation to starvation. Metabolic reprogramming is required for cancer cells shed into the peritoneal cavity to resist anoikis (i.e., programmed cell death). Profound changes in hexokinase metabolism are needed to compensate ineffective oxidative phosphorylation in mitochondria. During the development of PM, hypoxia inducible factor-1α (HIF-1α) plays a key role in activating both aerobic and anaerobic glycolysis, increasing the uptake of glucose, lipid, and glutamine into cancer cells. HIF-1α upregulates hexokinase II, phosphoglycerate kinase 1 (PGK1), pyruvate dehydrogenase kinase (PDK), pyruvate kinase muscle isoenzyme 2 (PKM2), lactate dehydrogenase (LDH) and glucose transporters (GLUT) and promotes cytoplasmic glycolysis. HIF-1α also stimulates the utilization of glutamine and fatty acids as alternative energy substrates. Cancer cells in the peritoneal cavity interact with cancer-associated fibroblasts and adipocytes to meet metabolic demands and incorporate autophagy products for growth. Therapy of CAS in PM is challenging. Optimal nutritional intake alone including total parenteral nutrition is unable to reverse CAS. Pressurized intraperitoneal aerosol chemotherapy (PIPAC) stabilized nutritional status in a significant proportion of PM patients. Agents targeting the mechanisms of CAS are under development.

Differential effects of a 40-hour fast and bile acid supplementation on human GLP-1 and FGF19 responses

Bile acids, glucagon-like peptide-1 (GLP-1), and fibroblast growth factor 19 (FGF19) play an important role in postprandial metabolism. In this study, we investigated the postprandial bile acid response in plasma and its relation to insulin, GLP-1, and FGF19. First, we investigated the postprandial response to 40-h fast. Then we administered glycine-conjugated deoxycholic acid (gDCA) with the meal. We performed two separate observational randomized crossover studies on healthy, lean men. In experiment 1: we tested 4-h mixed meal after an overnight fast and a 40-h fast. In experiment 2, we tested a 4-h mixed meal test with and without gDCA supplementation. Both studies measured postprandial glucose, insulin, bile acids, GLP-1, and FGF19. In experiment 1, 40 h of fasting induced insulin resistance and increased postprandial GLP-1 and FGF19 concentrations. After an overnight fast, we observed strong correlations between postprandial insulin and gDCA levels at specific time points. In experiment 2, administration of gDCA increased GLP-1 levels and lowered late postprandial glucose without effect on FGF19. Energy expenditure was not affected by gDCA administration. Unexpectedly, 40 h of fasting increased both GLP-1 and FGF19, where the former appeared bile acid independent and the latter bile acid dependent. Second, a single dose of gDCA increased postprandial GLP-1. Therefore, our data add complexity to the physiological regulation of the enterokines GLP-1 and FGF19 by bile acids.

Maternal Overfeeding during Lactation Impairs the Metabolic Response to Fed/Fasting Changing Conditions in the Postweaning Offspring

SCOPE

The metabolic response to fed/fasting changing conditions at early age in rats with different predisposition to obesity-related alterations due to maternal conditions during the perinatal period is studied.

METHODS AND RESULTS

Offspring of dams made obese by a cafeteria diet and moved to a normal-fat diet 1 month before gestation (O-PCaf, with an apparently normal phenotype in adulthood), and offspring of cafeteria diet-fed dams during lactation (O-CAF, with a thin-outside-fat inside phenotype), together with the offspring of control dams (O-C), are studied at early age. Fasting is associated with downregulation of lipogenesis-related genes in liver and rpWAT, and upregulation of genes related to lipolysis and fatty acid uptake in rpWAT in O-C animals. The response to fed/fasting conditions is impaired in O-CAF, but not in O-PCaf animals. The fasting-induced increase in the expression of Prkaa1 in liver and rpWAT, and the corresponding increase of hepatic AMPKα1 protein levels of O-C animals are attenuated in O-CAF rats, while no alterations are found in O-PCaf animals versus controls.

CONCLUSION

Maternal intake of a cafeteria diet during lactation causes early alterations in the offspring, impairing their metabolic flexibility in response to fed/fasting changing conditions, which may contribute to hindering energy homeostasis maintenance.

Effects of a 12-Week Very-Low Carbohydrate High-Fat Diet on Maximal Aerobic Capacity, High-Intensity Intermittent Exercise, and Cardiac Autonomic Regulation: Non-randomized Parallel-Group Study

Purpose

The aim of this non-randomized parallel group study was to examine the 12 week effects of a very low-carbohydrate high-fat diet (VLCHF) on maximal cardiorespiratory capacity, high-intensity interval training (HIIT) performance, and cardiac autonomic regulation.

Methods

Twenty-four recreationally trained participants allocated to either a VLCHF (N = 12) or a habitual diet (HD; N = 12) group completed 12 weeks of a diet and exercise (VLCHF) or an exercise only intervention (HD). Maximal graded exercise tests (GXT) were performed at baseline, after 4, 8, and 12 weeks. A supervised HIIT session and the 30-15 Intermittent Fitness Test (30-15_IFT) were conducted once a week.

Results

Total time to exhaustion (TTE) in both GXT and 30-15_IFTlargely increased in both VLCHF (p = 0.005, BF₁₀ = 11.30 and p = 0.001, BF₁₀ ≥ 100, respectively) and HD (p = 0.018, BF₁₀ = 3.87 and p = 0.001, BF₁₀ ≥ 100, respectively) groups after 12 weeks. Absolute maximal oxygen uptake (V˙O_2max) was not changed in both groups but relative V˙O_2max increased in VLCHF in concert with reductions in body mass (66.7 ± 10.2–63.1 ± 8.5 kg). Cardiac autonomic regulation did not reveal any between-group differences after 12 weeks. VLCHF diet induced an increase in β-hydroxybutyrate, which tended to normalize during the intervention period.

Conclusion

The 12 week VLCHF diet did not impair high-intensity continuous or intermittent exercise lasting up to 25 min, nor did it impair maximal cardiorespiratory performance or autonomic nervous system (ANS) activity.

Hierarchical activation of compartmentalized pools of AMPK depends on severity of nutrient or energy stress

AMPK, a master regulator of metabolic homeostasis, is activated by both AMP-dependent and AMP-independent mechanisms. The conditions under which these different mechanisms operate, and their biological implications are unclear. Here, we show that, depending on the degree of elevation of cellular AMP, distinct compartmentalized pools of AMPK are activated, phosphorylating different sets of targets. Low glucose activates AMPK exclusively through the AMP-independent, AXIN-based pathway in lysosomes to phosphorylate targets such as ACC1 and SREBP1c, exerting early anti-anabolic and pro-catabolic roles. Moderate increases in AMP expand this to activate cytosolic AMPK also in an AXIN-dependent manner. In contrast, high concentrations of AMP, arising from severe nutrient stress, activate all pools of AMPK independently of AXIN. Surprisingly, mitochondrion-localized AMPK is activated to phosphorylate ACC2 and mitochondrial fission factor (MFF) only during severe nutrient stress. Our findings reveal a spatiotemporal basis for hierarchical activation of different pools of AMPK during differing degrees of stress severity.

The Influence of Meal Frequency and Timing on Health in Humans: The Role of Fasting

The influence of meal frequency and timing on health and disease has been a topic of interest for many years. While epidemiological evidence indicates an association between higher meal frequencies and lower disease risk, experimental trials have shown conflicting results. Furthermore, recent prospective research has demonstrated a significant increase in disease risk with a high meal frequency (≥6 meals/day) as compared to a low meal frequency (1⁻2 meals/day). Apart from meal frequency and timing we also have to consider breakfast consumption and the distribution of daily energy intake, caloric restriction, and night-time eating. A central role in this complex scenario is played by the fasting period length between two meals. The physiological underpinning of these interconnected variables may be through internal circadian clocks, and food consumption that is asynchronous with natural circadian rhythms may exert adverse health effects and increase disease risk. Additionally, alterations in meal frequency and meal timing have the potential to influence energy and macronutrient intake.A regular meal pattern including breakfast consumption, consuming a higher proportion of energy early in the day, reduced meal frequency (i.e., 2⁻3 meals/day), and regular fasting periods may provide physiological benefits such as reduced inflammation, improved circadian rhythmicity, increased autophagy and stress resistance, and modulation of the gut microbiota.

Control and Regulation of Substrate Selection in Cytoplasmic and Mitochondrial Catabolic Networks. A Systems Biology Analysis

Appropriate substrate selection between fats and glucose is associated with the success of interventions that maintain health such as exercise or caloric restriction, or with the severity of diseases such as diabetes or other metabolic disorders. Although the interaction and mutual inhibition between glucose and fatty-acids (FAs) catabolism has been studied for decades, a quantitative and integrated understanding of the control and regulation of substrate selection through central catabolic pathways is lacking. We addressed this gap here using a computational model representing cardiomyocyte catabolism encompassing glucose (Glc) utilization, pyruvate transport into mitochondria and oxidation in the tricarboxylic acid (TCA) cycle, β-oxidation of palmitate (Palm), oxidative phosphorylation, ion transport, pH regulation, and ROS generation and scavenging in cytoplasmic and mitochondrial compartments. The model is described by 82 differential equations and 119 enzymatic, electron transport and substrate transport reactions accounting for regulatory mechanisms and key players, namely pyruvate dehydrogenase (PDH) and its modulation by multiple effectors. We applied metabolic control analysis to the network operating with various Glc to Palm ratios. The flux and metabolites’ concentration control were visualized through heat maps providing major insights into main control and regulatory nodes throughout the catabolic network. Metabolic pathways located in different compartments were found to reciprocally control each other. For example, glucose uptake and the ATP demand exert control on most processes in catabolism while TCA cycle activities and membrane-associated energy transduction reactions exerted control on mitochondrial processes namely β-oxidation. PFK and PDH, two highly regulated enzymes, exhibit opposite behavior from a control perspective. While PFK activity was a main rate-controlling step affecting the whole network, PDH played the role of a major regulator showing high sensitivity (elasticity) to substrate availability and key activators/inhibitors, a trait expected from a flexible substrate selector strategically located in the metabolic network. PDH regulated the rate of Glc and Palm consumption, consistent with its high sensitivity toward AcCoA, CoA, and NADH. Overall, these results indicate that the control of catabolism is highly distributed across the metabolic network suggesting that fuel selection between FAs and Glc goes well beyond the mechanisms traditionally postulated to explain the glucose-fatty-acid cycle.

24-h severe energy restriction impairs postprandial glycaemic control in young, lean males

Intermittent energy restriction (IER) involves short periods of severe energy restriction interspersed with periods of adequate energy intake, and can induce weight loss. Insulin sensitivity is impaired by short-term, complete energy restriction, but the effects of IER are not well known. In randomised order, fourteen lean men (age: 25 (sd 4) years; BMI: 24 (sd 2) kg/m2; body fat: 17 (4) %) consumed 24-h diets providing 100 % (10 441 (sd 812) kJ; energy balance (EB)) or 25 % (2622 (sd 204) kJ; energy restriction (ER)) of estimated energy requirements, followed by an oral glucose tolerance test (OGTT; 75 g of glucose drink) after fasting overnight. Plasma/serum glucose, insulin, NEFA, glucagon-like peptide-1 (GLP-1), glucose-dependent insulinotropic peptide (GIP) and fibroblast growth factor 21 (FGF21) were assessed before and after (0 h) each 24-h dietary intervention, and throughout the 2-h OGTT. Homoeostatic model assessment of insulin resistance (HOMA2-IR) assessed the fasted response and incremental AUC (iAUC) or total AUC (tAUC) were calculated during the OGTT. At 0 h, HOMA2-IR was 23 % lower after ER compared with EB (P<0·05). During the OGTT, serum glucose iAUC (P<0·001), serum insulin iAUC (P<0·05) and plasma NEFA tAUC (P<0·01) were greater during ER, but GLP-1 (P=0·161), GIP (P=0·473) and FGF21 (P=0·497) tAUC were similar between trials. These results demonstrate that severe energy restriction acutely impairs postprandial glycaemic control in lean men, despite reducing HOMA2-IR. Chronic intervention studies are required to elucidate the long-term effects of IER on indices of insulin sensitivity, particularly in the absence of weight loss.

Control of hepatic gluconeogenesis by Argonaute2

Objective

The liver performs a central role in regulating energy homeostasis by increasing glucose output during fasting. Recent studies on Argonaute2 (Ago2), a key RNA-binding protein mediating the microRNA pathway, have illustrated its role in adaptive mechanisms according to changes in metabolic demand. Here we sought to characterize the functional role of Ago2 in the liver in the maintenance of systemic glucose homeostasis.

Methods

We first analyzed Ago2 expression in mouse primary hepatocyte cultures after modulating extracellular glucose concentrations and in the presence of activators or inhibitors of glucokinase activity. We then characterized a conditional loss-of-function mouse model of Ago2 in liver for alterations in systemic energy metabolism.

Results

Here we show that Ago2 expression in liver is directly correlated to extracellular glucose concentrations and that modulating glucokinase activity is adequate to affect hepatic Ago2 levels. Conditional deletion of Ago2 in liver resulted in decreased fasting glucose levels in addition to reducing hepatic glucose production. Moreover, loss of Ago2 promoted hepatic expression of AMP-activated protein kinase α1 (AMPKα1) by de-repressing its targeting by miR-148a, an abundant microRNA in the liver. Deletion of Ago2 from hyperglycemic, obese, and insulin-resistant Lep^ob/ob mice reduced both random and fasted blood glucose levels and body weight and improved insulin sensitivity.

Conclusions

These data illustrate a central role for Ago2 in the adaptive response of the liver to fasting. Ago2 mediates the suppression of AMPKα1 by miR-148a, thereby identifying a regulatory link between non-coding RNAs and a key stress regulator in the hepatocyte.

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Hepatic Ago2 levels correlate with changes in extracellular glucose concentrations.

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Conditional deletion of Ago2 in liver decreased fasting glucose levels.

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Loss of Ago2 promoted AMPKα1 by de-repressing its targeting by miR-148a.

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Deletion of Ago2 from Lep^ob/ob mice improved glycemia and insulin sensitivity.

Metabolic Flexibility as an Adaptation to Energy Resources and Requirements in Health and Disease

The ability to efficiently adapt metabolism by substrate sensing, trafficking, storage, and utilization, dependent on availability and requirement, is known as metabolic flexibility. In this review, we discuss the breadth and depth of metabolic flexibility and its impact on health and disease. Metabolic flexibility is essential to maintain energy homeostasis in times of either caloric excess or caloric restriction, and in times of either low or high energy demand, such as during exercise. The liver, adipose tissue, and muscle govern systemic metabolic flexibility and manage nutrient sensing, uptake, transport, storage, and expenditure by communication via endocrine cues. At a molecular level, metabolic flexibility relies on the configuration of metabolic pathways, which are regulated by key metabolic enzymes and transcription factors, many of which interact closely with the mitochondria. Disrupted metabolic flexibility, or metabolic inflexibility, however, is associated with many pathological conditions including metabolic syndrome, type 2 diabetes mellitus, and cancer. Multiple factors such as dietary composition and feeding frequency, exercise training, and use of pharmacological compounds, influence metabolic flexibility and will be discussed here. Last, we outline important advances in metabolic flexibility research and discuss medical horizons and translational aspects.

Breath profiles of children on ketogenic therapy

Ketogenic diets (KDs) were initially introduced to clinical practices as alimentary approaches with the aim to control drug-resistant epilepsies. Over the decades, a large and growing body of research has addressed the antiseizure effect of various KDs, and worked out KD-based dietary regimens, including their acting factors and modes of action. KDs have also appeared in weight loss therapies. Therapy control, particularly at initiation, happens through regular blood analysis and control of urine ketone levels. However, there is a lack of fast, reliable, and preferably non-invasive methods to accomplish this. The detection of exhaled breath constituents may offer a solution. The exhaled breath contains hundreds of volatile organic compounds (VOCs), which can be modified by diet. VOC detection technology has resulted in low-cost sensors that can facilitate the self-monitoring of patients in the future if reliable breath markers are available. Therefore, it is of interest to investigate the composition of exhaled breath in children on KDs. Twenty-two pediatric patients between 4 and 18 years of age were recruited in this study. Eleven of them received a KD and suffered from epilepsy, with the exception of one child, who was admitted to a weight-reduction therapy. The control group involved 11 patients with neurological disorders but not on KD. Breath volatiles were analyzed using gas chromatography mass spectrometry (GC-MS) after preconcentration of the analytes on needle traps (NTs). We found that the breath concentrations of a number of VOCs, namely acetaldehyde, acetone, 2-methylfuran, methyl-vinyl-ketone, and 2-pentanone were significantly elevated in the breath of children on a KD in comparison to their control counterparts. Interestingly, breath ethanol was lower in patients on a KD than in non-KD patients. Association studies revealed an interrelationship among (i) lipid parameters and ketone bodies, (ii) methacrolein, methyl-vinyl-ketone, and high-density lipoprotein, as well as (iii) methyl-vinyl-ketone, acetone, and 2-pentanone, thus raising the possibility of a common metabolic source. The duration of diet was positively and negatively associated with breath acetone and breath ethanol, respectively. Some of the changes were linked to β-oxidation, but there are uncertainties in regard to metabolic sources of other metabolites. Lipid peroxidation and alteration of intestinal microbial composition may also be involved in the changes of VOC profiles during KD. Since lipids used for metabolism during KD originate from external sources, the processes occurring cannot simply be compared to and deduced from changes appearing in starvation; however, lipid mobilization is also evident in starvation. To find reliable and sensitive VOC markers that are linked to the respective ketogenic regimen, further investigations are needed to reveal the metabolic background.

Early Time-Restricted Feeding Improves Insulin Sensitivity, Blood Pressure, and Oxidative Stress Even without Weight Loss in Men with Prediabetes

Intermittent fasting (IF) improves cardiometabolic health; however, it is unknown whether these effects are due solely to weight loss. We conducted the first supervised controlled feeding trial to test whether IF has benefits independent of weight loss by feeding participants enough food to maintain their weight. Our proof-of-concept study also constitutes the first trial of early time-restricted feeding (eTRF), a form of IF that involves eating early in the day to be in alignment with circadian rhythms in metabolism. Men with prediabetes were randomized to eTRF (6-hr feeding period, with dinner before 3 p.m.) or a control schedule (12-hr feeding period) for 5 weeks and later crossed over to the other schedule. eTRF improved insulin sensitivity, β cell responsiveness, blood pressure, oxidative stress, and appetite. We demonstrate for the first time in humans that eTRF improves some aspects of cardiometabolic health and that IF's effects are not solely due to weight loss.

Effect of Toxicants on Fatty Acid Metabolism in HepG2 Cells

Impairment of hepatic fatty acid metabolism can lead to liver steatosis and injury. Testing drugs for interference with hepatic fatty acid metabolism is therefore important. To find out whether HepG2 cells are suitable for this purpose, we investigated the effect of three established fatty acid metabolism inhibitors and of three test compounds on triglyceride accumulation, palmitate metabolism, the acylcarnitine pool and dicarboxylic acid accumulation in the cell supernatant and on ApoB-100 excretion in HepG2 cells. The three established inhibitors [etomoxir, methylenecyclopropylacetic acid (MCPA), and 4-bromocrotonic acid (4-BCA)] depleted mitochondrial ATP at lower concentrations than cytotoxicity occurred, suggesting mitochondrial toxicity. They inhibited palmitate metabolism at similar or lower concentrations than ATP depletion, and 4-BCA was associated with cellular fat accumulation. They caused specific changes in the acylcarnitine pattern and etomoxir an increase of thapsic (C18 dicarboxylic) acid in the cell supernatant, and did not interfere with ApoB-100 excretion (marker of VLDL export). The three test compounds (amiodarone, tamoxifen, and the cannabinoid WIN 55,212-2) depleted the cellular ATP content at lower concentrations than cytotoxicity occurred. They all caused cellular fat accumulation and inhibited palmitate metabolism at similar or higher concentrations than ATP depletion. They suppressed medium-chain acylcarnitines in the cell supernatant and amiodarone and tamoxifen impaired thapsic acid production. Tamoxifen and WIN 55,212-2 decreased cellular ApoB-100 excretion. In conclusion, the established inhibitors of fatty acid metabolism caused the expected effects in HepG2 cells. HepG cells proved to be useful for the detection of drug-associated toxicities on hepatocellular fatty acid metabolism.

The Role of Leptin in Maintaining Plasma Glucose During Starvation

For 20 years it has been known that concentrations of leptin, a hormone produced by the white adipose tissue (WAT) largely in proportion to body fat, drops precipitously with starvation, particularly in lean humans and animals. The role of leptin to suppress the thyroid and reproductive axes during a prolonged fast has been well defined; however, the impact of leptin on metabolic regulation has been incompletely understood. However emerging evidence suggests that, in starvation, hypoleptinemia increases activity of the hypothalamic-pituitary-adrenal axis, promoting WAT lipolysis, increasing hepatic acetyl-CoA concentrations, and maintaining euglycemia. In addition, leptin may be largely responsible for mediating a shift from a reliance upon glucose metabolism (absorption and glycogenolysis) to fat metabolism (lipolysis increasing gluconeogenesis) which preserves substrates for the brain, heart, and other critical organs. In this way a leptin-mediated glucose-fatty acid cycle appears to maintain glycemia and permit survival in starvation.

Intermittent fasting and cardiovascular disease: current evidence and unresolved questions

Intermittent fasting has produced a variety of beneficial health effects in animal models, although high-quality research in humans has been limited. This special report examines current evidences for intermittent fasting in humans, discusses issues that require further examination, and recommends new research that can improve the knowledge base in this emerging research area. While potentially useful for health improvement, intermittent fasting requires further study prior to widespread implementation for health purposes. Randomized, longer-term studies are needed to determine whether using intermittent fasting as a lifestyle rather than a diet is feasible and beneficial for the health of some members of the human population.

Plasma acylcarnitine concentrations reflect the acylcarnitine profile in cardiac tissues

Increased plasma concentrations of acylcarnitines (ACs) are suggested as a marker of metabolism disorders. The aim of the present study was to clarify which tissues are responsible for changes in the AC pool in plasma. The concentrations of medium- and long-chain ACs were changing during the fed-fast cycle in rat heart, muscles and liver. After 60 min running exercise, AC content was increased in fasted mice muscles, but not in plasma or heart. After glucose bolus administration in fasted rats, the AC concentrations in plasma decreased after 30 min but then began to increase, while in the muscles and liver, the contents of medium- and long-chain ACs were unchanged or even increased. Only the heart showed a decrease in medium- and long-chain AC contents that was similar to that observed in plasma. In isolated rat heart, but not isolated-contracting mice muscles, the significant efflux of medium- and long-chain ACs was observed. The efflux was reduced by 40% after the addition of glucose and insulin to the perfusion solution. Overall, these results indicate that during fed-fast cycle shifting the heart determines the medium- and long-chain AC profile in plasma, due to a rapid response to the availability of circulating energy substrates.

A high-fat diet is deleterious to mice under glycolysis restriction

It is debated whether carbohydrate restriction has metabolic advantage for its variable weight loss. Five-week-old male mice fed a high-fat diet and receiving a glycolytic inhibitor, 2-deoxyglucose, died within 9 days. They exhibited greater decreases in rectal temperature, appetite, and decline in body weight accompanied by increasing total cholesterol level than the other groups. This study suggests that carbohydrate is necessary for adequate physical and metabolic performance when lipid-rich diet is loaded.

Early or Late Feeding after ICU Admission?

The feeding of critically ill patients has recently become a controversial issue, as several studies have provided unexpected and contradictory results. Earlier beliefs regarding energy requirements in critical illness-especially during the initial phase-have been challenged. In the current review, we summarize existing evidence about fasting and the impact of early vs. late feeding on the sick organism's responses. The most important points are the non-nutritional advantages of using the intestine, and recognition that early endogenous energy production as an important player in the response must be integrated in the nutrient prescription. There is as of yet no bedside tool to monitor dynamics in metabolism and the magnitude of the endogenous energy production. Hence, an early "full-feeding strategy" exposes patients to involuntary overfeeding, due to the absence of an objective measure enabling the adjustment of the nutritional therapy. Suggestions for future research and clinical practice are proposed.

A transcriptomic approach to study the effect of long-term starvation and diet composition on the expression of mitochondrial oxidative phosphorylation genes in gilthead sea bream (Sparus aurata)

Background

The impact of nutritional status and diet composition on mitochondrial oxidative phosphorylation (OXPHOS) in fish remains largely unknown. To identify biomarkers of interest in nutritional studies, herein we obtained a deep-coverage transcriptome by 454 pyrosequencing of liver and skeletal muscle cDNA normalised libraries from long-term starved gilthead sea bream (Sparus aurata) and fish fed different diets.

Results

After clean-up of high-throughput deep sequencing reads, 699,991 and 555,031 high-quality reads allowed de novo assembly of liver and skeletal muscle sequences, respectively (average length: 374 and 441 bp; total megabases: 262 and 245 Mbp). An additional incremental assembly was completed by integrating data from both tissues (hybrid assembly). Assembly of hybrid, liver and skeletal muscle transcriptomes yielded, respectively, 19,530, 11,545 and 10,599 isotigs (average length: 1330, 1208 and 1390 bp, respectively) that were grouped into 15,954, 10,033 and 9189 isogroups. Following annotation, hybrid transcriptomic data were used to construct an oligonucleotide microarray to analyse nutritional regulation of the expression of 129 genes involved in OXPHOS in S. aurata. Starvation upregulated cytochrome c oxidase components and other key OXPHOS genes in the liver, which exhibited higher sensitive to food deprivation than the skeletal muscle. However, diet composition affected OXPHOS in the skeletal muscle to a greater extent than in the liver: most of genes upregulated under starvation presented higher expression among fish fed a high carbohydrate/low protein diet.

Conclusions

Our findings indicate that the expression of coenzyme Q-binding protein (COQ10), cytochrome c oxidase subunit 6A2 (COX6A2) and ADP/ATP translocase 3 (SLC25A6) in the liver, and cytochrome c oxidase subunit 5B isoform 1 (COX5B1) in the liver and the skeletal muscle, are sensitive markers of the nutritional condition that may be relevant to assess the effect of changes in the feeding regime and diet composition on fish farming.

Electronic supplementary material

The online version of this article (10.1186/s12864-017-4148-x) contains supplementary material, which is available to authorized users.

Low carbohydrate, high fat diet impairs exercise economy and negates the performance benefit from intensified training in elite race walkers

KEY POINTS

Three weeks of intensified training and mild energy deficit in elite race walkers increases peak aerobic capacity independent of dietary support. Adaptation to a ketogenic low carbohydrate, high fat (LCHF) diet markedly increases rates of whole-body fat oxidation during exercise in race walkers over a range of exercise intensities. The increased rates of fat oxidation result in reduced economy (increased oxygen demand for a given speed) at velocities that translate to real-life race performance in elite race walkers. In contrast to training with diets providing chronic or periodised high carbohydrate availability, adaptation to an LCHF diet impairs performance in elite endurance athletes despite a significant improvement in peak aerobic capacity.

ABSTRACT

We investigated the effects of adaptation to a ketogenic low carbohydrate (CHO), high fat diet (LCHF) during 3 weeks of intensified training on metabolism and performance of world-class endurance athletes. We controlled three isoenergetic diets in elite race walkers: high CHO availability (g kg^-1  day^-1 : 8.6 CHO, 2.1 protein, 1.2 fat) consumed before, during and after training (HCHO, n = 9); identical macronutrient intake, periodised within or between days to alternate between low and high CHO availability (PCHO, n = 10); LCHF (< 50 g day^-1 CHO; 78% energy as fat; 2.1 g kg^-1  day^-1 protein; LCHF, n = 10). Post-intervention, V̇O2 peak during race walking increased in all groups (P < 0.001, 90% CI: 2.55, 5.20%). LCHF was associated with markedly increased rates of whole-body fat oxidation, attaining peak rates of 1.57 ± 0.32 g min^-1 during 2 h of walking at ∼80% V̇O2 peak . However, LCHF also increased the oxygen (O₂ ) cost of race walking at velocities relevant to real-life race performance: O₂ uptake (expressed as a percentage of new V̇O2 peak ) at a speed approximating 20 km race pace was reduced in HCHO and PCHO (90% CI: -7.047, -2.55 and -5.18, -0.86, respectively), but was maintained at pre-intervention levels in LCHF. HCHO and PCHO groups improved times for 10 km race walk: 6.6% (90% CI: 4.1, 9.1%) and 5.3% (3.4, 7.2%), with no improvement (-1.6% (-8.5, 5.3%)) for the LCHF group. In contrast to training with diets providing chronic or periodised high-CHO availability, and despite a significant improvement in V̇O2 peak , adaptation to the topical LCHF diet negated performance benefits in elite endurance athletes, in part due to reduced exercise economy.

Potential Benefits and Harms of Intermittent Energy Restriction and Intermittent Fasting Amongst Obese, Overweight and Normal Weight Subjects-A Narrative Review of Human and Animal Evidence

Intermittent energy restriction (IER) has become popular as a means of weight control amongst people who are overweight and obese, and is also undertaken by normal weight people hoping spells of marked energy restriction will optimise their health. This review summarises randomised comparisons of intermittent and isoenergetic continuous energy restriction for weight loss to manage overweight and obesity. It also summarises the potential beneficial or adverse effects of IER on body composition, adipose stores and metabolic effects from human studies, including studies amongst normal weight subjects and relevant animal experimentation. Six small short term (<6 month) studies amongst overweight or obese individuals indicate that intermittent energy restriction is equal to continuous restriction for weight loss, with one study reporting greater reductions in body fat, and two studies reporting greater reductions in HOMA insulin resistance in response to IER, with no obvious evidence of harm. Studies amongst normal weight subjects and different animal models highlight the potential beneficial and adverse effects of intermittent compared to continuous energy restriction on ectopic and visceral fat stores, adipocyte size, insulin resistance, and metabolic flexibility. The longer term benefits or harms of IER amongst people who are overweight or obese, and particularly amongst normal weight subjects, is not known and is a priority for further investigation.

Effects of acute dietary weight loss on postprandial plasma bile acid responses in obese insulin resistant subjects

BACKGROUND & AIMS

Bile acids (BA) are pleiotropic hormones affecting glucose and lipid metabolism. The physiochemical properties of different BA species affect their enterohepatic dynamics and their affinity for bile acid receptors. The BA pool composition is altered in patients with type 2 diabetes and obesity. In this study we used a 2-week very-low-calorie diet (VLCD) to investigate the effects of weight loss on BA pool composition and postprandial dynamics.

METHODS

We performed mixed meal tests in obese, insulin resistant subjects before and after the VLCD. We measured postprandial plasma levels of glucose, insulin, BA and the BA-induced enterokine fibroblast growth factor 19 (FGF19).

RESULTS

The VLCD decreased weight by 4.5 ± 2.3 kg (p < 0.0001) within 14 days. Weight loss increased peak postprandial deoxycholate (DCA) levels (median [IQR]: 0.90 [0.90] vs. 1.25 [1.35] μmol/L; p = 0.045*). Other BA species, glucose, insulin and FGF19 levels and prandial excursions were not significantly affected. The VLCD decreased resting and postprandial energy expenditure by 7 and 11% respectively.

CONCLUSIONS

VLCD induced weight loss increased postprandial DCA peak levels and decreased resting energy expenditure in obese insulin resistant subjects.

A Systematic Literature Review and Meta-Regression Analysis on Early-Life Energy Restriction and Cancer Risk in Humans

Background

In animal models, long-term moderate energy restriction (ER) is reported to decelerate carcinogenesis, whereas the effect of severe ER is inconsistent. The impact of early-life ER on cancer risk has never been reviewed systematically and quantitatively based on observational studies in humans.

Objective

We conducted a systematic review of observational studies and a meta-(regression) analysis on cohort studies to clarify the association between early-life ER and organ site-specific cancer risk.

Methods

PubMed and EMBASE (1982 –August 2015) were searched for observational studies. Summary relative risks (RRs) were estimated using a random effects model when available ≥3 studies.

Results

Twenty-four studies were included. Eleven publications, emanating from seven prospective cohort studies and some reporting on multiple cancer endpoints, met the inclusion criteria for quantitative analysis. Women exposed to early-life ER (ranging from 220–1660 kcal/day) had a higher breast cancer risk than those not exposed (RR_{RE all ages} = 1.28, 95% CI: 1.05–1.56; RR_{RE for 10–20 years of age} = 1.21, 95% CI: 1.09–1.34). Men exposed to early-life ER (ranging from 220–800kcal/day) had a higher prostate cancer risk than those not exposed (RR_RE = 1.16, 95% CI: 1.03–1.30). Summary relative risks were not computed for colorectal cancer, because of heterogeneity, and for stomach-, pancreas-, ovarian-, and respiratory cancer because there were <3 available studies. Longer duration of exposure to ER, after adjustment for severity, was positively associated with overall cancer risk in women (p = 0.02). Ecological studies suggest that less severe ER is generally associated with a reduced risk of cancer.

Conclusions

Early-life transient severe ER seems to be associated with increased cancer risk in the breast (particularly ER exposure at adolescent age) and prostate. The duration, rather than severity of exposure to ER, seems to positively influence relative risk estimates. This result should be interpreted with caution due to the limited number of studies and difficulty in disentangling duration, severity, and geographical setting of exposure.

Normoxic or hypoxic adaptation in response to antiangiogenic therapy: Clinical implications

In a recent article in Cell Reports, we described a novel mechanism for acquired resistance against new small-molecule antiangiogenic tyrosine-kinase inhibitors (TKIs). Vascular normalization-inducing TKIs block glycolysis and trigger a nutritional stress response in the tumor compartment that induces a (targetable) switch to mitochondrial metabolism. We discuss the implications for clinical/translational studies and suggest areas for future research.

Assessment of plasma acylcarnitines before and after weight loss in obese subjects

Acylcarnitines, fatty acid oxidation (FAO) intermediates, have been implicated in diet-induced insulin resistance and type 2 diabetes mellitus, as increased levels are found in obese insulin resistant humans. Moreover plasma acylcarnitines have been associated with clinical parameters related to glucose metabolism, such as fasting glucose levels and HbA1c. We hypothesized that plasma acylcarnitines would correlate with energy expenditure, insulin sensitivity and other clinical parameters before and during a weight loss intervention. We measured plasma acylcarnitines in 60 obese subjects before and after a 12 week weight loss intervention. These samples originated from three different interventions (diet alone (n = 20); diet and exercise (n = 21); diet and drug treatment (n = 19)). Acylcarnitine profiles were analysed in relation to clinical parameters of glucose metabolism, insulin sensitivity and energy expenditure. Conclusions were drawn from all 60 subjects together. Despite amelioration of HOMA-IR, plasma acylcarnitines levels increased during weight loss. HOMA-IR, energy expenditure and respiratory exchange ratio were not related to plasma acylcarnitines. However non-esterified fatty acids correlated strongly with several acylcarnitines at baseline and during the weight loss intervention (p < 0.001). Acylcarnitines did not correlate with clinical parameters of glucose metabolism during weight loss, questioning their role in insulin resistance and type 2 diabetes mellitus.

Targeting Tumor Mitochondrial Metabolism Overcomes Resistance to Antiangiogenics

Epithelial malignancies are effectively treated by antiangiogenics; however, acquired resistance is a major problem in cancer therapeutics. Epithelial tumors commonly have mutations in the MAPK/Pi3K-AKT pathways, which leads to high-rate aerobic glycolysis. Here, we show how multikinase inhibitor antiangiogenics (TKIs) induce hypoxia correction in spontaneous breast and lung tumor models. When this happens, the tumors downregulate glycolysis and switch to long-term reliance on mitochondrial respiration. A transcriptomic, metabolomic, and phosphoproteomic study revealed that this metabolic switch is mediated by downregulation of HIF1α and AKT and upregulation of AMPK, allowing uptake and degradation of fatty acids and ketone bodies. The switch renders mitochondrial respiration necessary for tumor survival. Agents like phenformin or ME344 induce synergistic tumor control when combined with TKIs, leading to metabolic synthetic lethality. Our study uncovers mechanistic insights in the process of tumor resistance to TKIs and may have clinical applicability.

Preoperative octreotide therapy and surgery in acromegaly: associations between glucose homeostasis and treatment response

In acromegaly, high GH/IGF-1 levels associate with abnormal glucose metabolism. Somatostatin analogs (SSAs) reduce GH and IGF-1 but inhibit insulin secretion. We studied glucose homeostasis in de novo patients with acromegaly and changes in glucose metabolism after treatment with SSA and surgery. In this post hoc analysis from a randomized controlled trial, 55 de novo patients with acromegaly, not using antidiabetic medication, were included. Before surgery, 26 patients received SSAs for 6 months. HbA1c, fasting glucose, and oral glucose tolerance test were performed at baseline, after SSA pretreatment and at 3 months postoperative. Area under curve of glucose (AUC-G) was calculated. Glucose homeostasis was compared to baseline levels of GH and IGF-1, change after SSA pretreatment, and remission both after SSA pretreatment and 3 months postoperative. In de novo patients, IGF-1/GH levels did not associate with baseline glucose parameters. After SSA pretreatment, changes in GH/IGF-1 correlated positively to change in HbA1c levels (both p < 0.03). HbA1c, fasting glucose, and AUC-G increased significantly during SSA pretreatment in patients not achieving hormonal control (all p < 0.05) but did not change significantly in patients with normalized hormone levels. At 3 months postoperative, HbA1c, fasting glucose, and AUC-G were significantly reduced in both cured and not cured patients (all p < 0.05). To conclude, in de novo patients with acromegaly, disease activity did not correlate with glucose homeostasis. Surgical treatment of acromegaly improved glucose metabolism in both cured and not cured patients, while SSA pretreatment led to deterioration in glucose homeostasis in patients not achieving biochemical control.

Investigation into the acute effects of total and partial energy restriction on postprandial metabolism among overweight/obese participants

The intermittent energy restriction (IER) approach to weight loss involves short periods of substantial (75-100 %) energy restriction (ER) interspersed with normal eating. This study aimed to characterise the early metabolic response to these varying degrees of ER, which occurs acutely and prior to weight loss. Ten (three female) healthy, overweight/obese participants (36 (SEM 5) years; 29·0 (sem 1·1) kg/m2) took part in this acute three-way cross-over study. Participants completed three 1-d dietary interventions in a randomised order with a 1-week washout period: isoenergetic intake, partial 75 % ER and total 100 % ER. Fasting and postprandial (6-h) metabolic responses to a liquid test meal were assessed the following morning via serial blood sampling and indirect calorimetry. Food intake was also recorded for two subsequent days of ad libitum intake. Relative to the isoenergetic control, postprandial glucose responses were increased following total ER (+142 %; P=0·015) and to a lesser extent after partial ER (+76 %; P=0·051). There was also a delay in the glucose time to peak after total ER only (P=0·024). Both total and partial ER interventions produced comparable reductions in postprandial TAG responses (-75 and -59 %, respectively; both P<0·05) and 3-d energy intake deficits of approximately 30 % (both P=0·015). Resting and meal-induced thermogenesis were not significantly affected by either ER intervention. In conclusion, our data demonstrate the ability of substantial ER to acutely alter postprandial glucose-lipid metabolism (with partial ER producing the more favourable overall response), as well as incomplete energy-intake compensation amongst overweight/obese participants. Further investigations are required to establish how metabolism adapts over time to the repeated perturbations experienced during IER, as well as the implications for long-term health.

Effects of intermittent fasting on body composition and clinical health markers in humans

Intermittent fasting is a broad term that encompasses a variety of programs that manipulate the timing of eating occasions by utilizing short-term fasts in order to improve body composition and overall health. This review examines studies conducted on intermittent fasting programs to determine if they are effective at improving body composition and clinical health markers associated with disease. Intermittent fasting protocols can be grouped into alternate-day fasting, whole-day fasting, and time-restricted feeding. Alternate-day fasting trials of 3 to 12 weeks in duration appear to be effective at reducing body weight (≈3%-7%), body fat (≈3-5.5 kg), total cholesterol (≈10%-21%), and triglycerides (≈14%-42%) in normal-weight, overweight, and obese humans. Whole-day fasting trials lasting 12 to 24 weeks also reduce body weight (≈3%-9%) and body fat, and favorably improve blood lipids (≈5%-20% reduction in total cholesterol and ≈17%-50% reduction in triglycerides). Research on time-restricted feeding is limited, and clear conclusions cannot be made at present. Future studies should examine long-term effects of intermittent fasting and the potential synergistic effects of combining intermittent fasting with exercise.

Obesity, the deadly quartet and the contribution of the neglected daily organ rest - a new dimension of un-health and its prevention

The "deadly quartet": excessive weight, hypertension, impaired glucose homeostasis, and atherogenic dyslipidemia constitute a greater threat to health than the added effects of smoking and alcohol abuse. It is strongly associated with unrestricted consumption of processed, refined foods. Recent observations from experience in South East Asia shows that the interval between lifestyle changes and associated change in disease pattern is shorter than earlier believed. Recent experience from obesity studies in Africa demonstrates not only dramatic changes in health but also large social consequences from being overweight. Obesity is not only a result of overeating - dozens of other factors are known to contribute. Our palaeolithic forefathers and those living a similar lifestyle today are reported to rarely have diseases and to live a long life. One such group is the Hunzas, living in Northern Pakistan, are reported to live on a daily 1,800-calorie 99% plant-based diet, consisting in 73% of mostly unrefined/unprocessed carbohydrates, 17% fat and 10% protein. They, and most likely also our forefathers, do/did most likely only eat twice a day, at noon and early evening. Calorie-restriction (CR) and also fasting was early recommended and has been so during thousands of years - early Greek medicine and giants such as Hippocrates, Galenus and later also Paracelsus prescribed restrictions in eating and fasting. So did Middle Age physicians and other nutrition experts such as Louis Cornado. Today it is again practiced around the World. Overeating and heavy postprandial metabolism is a great burden to the body causing elevated levels in blood of endotoxin, increased inflammatory and oxidative stress, release of tumor necrosis factor-α, and other pro-inflammatory cytokines, increases in numbers of and activating of leukocytes, a reaction that is potentiated by the presence of large-chain fatty acids and sugars. Various metabolic, uremic, microbiota-derived and environmental poisons accumulate in large amounts in the adipose tissues. High levels of poisons in the adipose tissues decreases the turnover of fats in order to protect other organs. The content in adipose of POPs - altogether 17 dioxins/furans and 18 polychlorinated biphenyl congeners, has been reported to be 2-3 times higher in obese compared to lean persons. Daily fasting consisting in 16 to 18 hours of avoidance of calorie intake offers an interesting alternative. An attractive policy is to abstain from eating between 18:00 in the evening and 10:00 or 12:00 AM, a plan, which I personally have practiced during many years.

Physiology of proglucagon peptides: role of glucagon and GLP-1 in health and disease

The preproglucagon gene (Gcg) is expressed by specific enteroendocrine cells (L-cells) of the intestinal mucosa, pancreatic islet α-cells, and a discrete set of neurons within the nucleus of the solitary tract. Gcg encodes multiple peptides including glucagon, glucagon-like peptide-1, glucagon-like peptide-2, oxyntomodulin, and glicentin. Of these, glucagon and GLP-1 have received the most attention because of important roles in glucose metabolism, involvement in diabetes and other disorders, and application to therapeutics. The generally accepted model is that GLP-1 improves glucose homeostasis indirectly via stimulation of nutrient-induced insulin release and by reducing glucagon secretion. Yet the body of literature surrounding GLP-1 physiology reveals an incompletely understood and complex system that includes peripheral and central GLP-1 actions to regulate energy and glucose homeostasis. On the other hand, glucagon is established principally as a counterregulatory hormone, increasing in response to physiological challenges that threaten adequate blood glucose levels and driving glucose production to restore euglycemia. However, there also exists a potential role for glucagon in regulating energy expenditure that has recently been suggested in pharmacological studies. It is also becoming apparent that there is cross-talk between the proglucagon derived-peptides, e.g., GLP-1 inhibits glucagon secretion, and some additive or synergistic pharmacological interaction between GLP-1 and glucagon, e.g., dual glucagon/GLP-1 agonists cause more weight loss than single agonists. In this review, we discuss the physiological functions of both glucagon and GLP-1 by comparing and contrasting how these peptides function, variably in concert and opposition, to regulate glucose and energy homeostasis.

Short-term fasting alters cytochrome P450-mediated drug metabolism in humans

Experimental studies indicate that short-term fasting alters drug metabolism. However, the effects of short-term fasting on drug metabolism in humans need further investigation. Therefore, the aim of this study was to evaluate the effects of short-term fasting (36 h) on P450-mediated drug metabolism. In a randomized crossover study design, nine healthy subjects ingested a cocktail consisting of five P450-specific probe drugs [caffeine (CYP1A2), S-warfarin (CYP2C9), omeprazole (CYP2C19), metoprolol (CYP2D6), and midazolam (CYP3A4)] on two occasions (control study after an overnight fast and after 36 h of fasting). Blood samples were drawn for pharmacokinetic analysis using nonlinear mixed effects modeling. In addition, we studied in Wistar rats the effects of short-term fasting on hepatic mRNA expression of P450 isoforms corresponding with the five studied P450 enzymes in humans. In the healthy subjects, short-term fasting increased oral caffeine clearance by 20% (P = 0.03) and decreased oral S-warfarin clearance by 25% (P < 0.001). In rats, short-term fasting increased mRNA expression of the orthologs of human CYP1A2, CYP2C19, CYP2D6, and CYP3A4 (P < 0.05), and decreased the mRNA expression of the ortholog of CYP2C9 (P < 0.001) compared with the postabsorptive state. These results demonstrate that short-term fasting alters cytochrome P450-mediated drug metabolism in a nonuniform pattern. Therefore, short-term fasting is another factor affecting cytochrome P450-mediated drug metabolism in humans.

Fasting and exercise differentially regulate BDNF mRNA expression in human skeletal muscle

Brain-derived neurotrophic factor (BDNF) gene expression was measured in human skeletal muscle following 3 intensities of exercise and a 48-h fast. No change in BDNF mRNA was observed following exercise, while fasting upregulated BDNF by ∼3.5-fold. These changes were dissociated from changes in peroxisome proliferator-activated receptor gamma coactivator 1 alpha (PGC-1α) following exercise (+2- to 15-fold) and fasting (∼–25%). These results challenge our understanding of the response of BDNF to energetic stress and highlight the importance of future work in this area.

Malnutrition-induced Wernicke's encephalopathy following a water-only fasting diet

BACKGROUND

Wernicke's encephalopathy is a critical condition of neurological dysfunction resulting from a deficiency in thiamine. Chronic alcoholism is recognized as the most common cause of Wernicke's encephalopathy, but other causes, including fasting/starvation and malnutrition, have been documented within the scientific literature. These causes may not be readily recognized by healthcare professionals and may lead to Wernicke's encephalopathy being overlooked as a diagnosis when a nonalcoholic patient presents with classic signs and symptoms of the disorder.

MATERIALS AND METHODS

A narrative review of thiamine and its relationship to the development, diagnosis, and treatment of Wernicke's encephalopathy is presented based on a review of evidence-based guidelines and published research. To heighten awareness of the development of Wernicke's encephalopathy in fasted/starved and malnourished patients and to contribute to the scientific body of knowledge for the identification and management of Wernicke's encephalopathy in these patients, the clinical course and treatment of an adult woman who developed Wernicke's encephalopathy following a 40-day water-only fasting diet is outlined.

RESULTS

Clinical suspicion was required to identify the patient's condition and initiate immediate intervention through parenteral thiamine administration. Oral thiamine supplementation of 100 to 800 mg per day for 6 months was required to aid recovery.

OUTCOMES

The patient's clinical course and response to treatment illustrate the necessity for clinical awareness and suspicion of Wernicke's encephalopathy among healthcare professionals, timely and adequate parenteral thiamine administration, and oral thiamine supplementation at therapeutic doses to correct the nutrient deficiency, halt the progression of Wernicke's encephalopathy, and promote recovery.

Regulation of skeletal muscle energy/nutrient-sensing pathways during metabolic adaptation to fasting in healthy humans

During fasting, rapid metabolic adaptations are required to maintain energy homeostasis. This occurs by a coordinated regulation of energy/nutrient-sensing pathways leading to transcriptional activation and repression of specific sets of genes. The aim of the study was to investigate how short-term fasting affects whole body energy homeostasis and skeletal muscle energy/nutrient-sensing pathways and transcriptome in humans. For this purpose, 12 young healthy men were studied during a 24-h fast. Whole body glucose/lipid oxidation rates were determined by indirect calorimetry, and blood and skeletal muscle biopsies were collected and analyzed at baseline and after 10 and 24 h of fasting. As expected, fasting induced a time-dependent decrease in plasma insulin and leptin levels, whereas levels of ketone bodies and free fatty acids increased. This was associated with a metabolic shift from glucose toward lipid oxidation. At the molecular level, activation of the protein kinase B (PKB/Akt) and mammalian target of rapamycin pathways was time-dependently reduced in skeletal muscle during fasting, whereas the AMP-activated protein kinase activity remained unaffected. Furthermore, we report some changes in the phosphorylation and/or content of forkhead protein 1, sirtuin 1, and class IIa histone deacetylase 4, suggesting that these pathways might be involved in the transcriptional adaptation to fasting. Finally, transcriptome profiling identified genes that were significantly regulated by fasting in skeletal muscle at both early and late time points. Collectively, our study provides a comprehensive map of the main energy/nutrient-sensing pathways and transcriptomic changes during short-term adaptation to fasting in human skeletal muscle.

Link between insulin resistance and hypertension: What is the evidence from evolutionary biology?

Insulin resistance and hypertension are considered as prototypical "diseases of civilization" that are manifested in the modern environment as plentiful food and sedentary life. The human propensity for insulin resistance and hypertension is a product, at least in part, of our evolutionary history. Adaptation to ancient lifestyle characterized by a low sodium, low-calorie food supply and physical stress to injury response has driven our evolution to shape and preserve a thrifty genotype, which is favorite with energy-saving and sodium conservation. As our civilization evolved, a sedentary lifestyle and sodium- and energy-rich diet, the thrifty genotype is no longer advantageous, and may be maladaptive to disease phenotype, such as hypertension, obesity and insulin resistance syndrome. This article reviews human evolution and the impact of the modern environment on hypertension and insulin resistance.

Effects of prolonged fasting on AMPK signaling, gene expression, and mitochondrial respiratory chain content in skeletal muscle from lean and obese individuals

Obesity in humans is often associated with metabolic inflexibility, but the underlying molecular mechanisms remain incompletely understood. The aim of the present study was to investigate how adaptation to prolonged fasting affects energy/nutrient-sensing pathways and metabolic gene expression in skeletal muscle from lean and obese individuals. Twelve lean and 14 nondiabetic obese subjects were fasted for 48 h. Whole body glucose/lipid oxidation rates were determined by indirect calorimetry, and blood and skeletal muscle biopsies were collected and analyzed. In response to fasting, body weight loss was similar in both groups, but the decrease in plasma insulin and leptin and the concomitant increase in growth hormone were significantly attenuated in obese subjects. The fasting-induced shift from glucose toward lipid oxidation was also severely blunted. At the molecular level, the expression of insulin receptor-β (IRβ) was lower in skeletal muscle from obese subjects at baseline, whereas the fasting-induced reductions in insulin signaling were similar in both groups. The protein expression of mitochondrial respiratory chain components, although not modified by fasting, was significantly reduced in obese subjects. Some minor differences in metabolic gene expression were observed at baseline and in response to fasting. Surprisingly, fasting reduced AMPK activity in lean but not in obese subjects, whereas the expression of AMPK subunits was not affected. We conclude that whole body metabolic inflexibility in response to prolonged fasting in obese humans is associated with lower skeletal muscle IRβ and mitochondrial respiratory chain content as well as a blunted decline of AMPK activity.