Ethanol acutely impairs glycogen repletion in skeletal muscle following high intensity short duration exercise in the rat

Non-carbohydrate Dietary Factors and Their Influence on Post-Exercise Glycogen Storage: a Review

The optimization of post-exercise glycogen synthesis can improve endurance performance, delay fatigue in subsequent bouts, and accelerate recovery from exercise. High carbohydrate intakes (1.2 g/kg of body weight/h) are recommended in the first 4 h after exercise. However, athletes may struggle to consume carbohydrates at those levels. PURPOSE OF REVIEW: Thus, we aimed to determine whether the consumption of non-carbohydrate dietary factors (creatine, glutamine, caffeine, flavonoids, and alcohol) enhances post-exercise glycogen synthesis. RECENT FINDINGS: Trained athletes may not realize the benefits of creatine loading on glycogen synthesis. The impacts of caffeine, glutamine, flavonoids, and alcohol on post-exercise glycogen synthesis are poorly understood. Other ergogenic benefits to exercise performance, however, have been reported for creatine, glutamine, caffeine, and flavonoids, which were beyond the scope of this review. Evidence in trained athletes is limited and inconclusive on the impact of these non-carbohydrate dietary factors on post-exercise glycogen synthesis.

Nutrition and Alcoholic Liver Disease: Effects of Alcoholism on Nutrition, Effects of Nutrition on Alcoholic Liver Disease, and Nutritional Therapies for Alcoholic Liver Disease

Malnutrition is the most frequent and nearly universal consequence in alcoholic liver disease (ALD) that adversely affects clinical outcomes. Sarcopenia or skeletal muscle loss is the major component of malnutrition in liver disease. There are no effective therapies to prevent or reverse sarcopenia in ALD because the mechanisms are not well understood. Consequences of liver disease including hyperammonemia, hormonal perturbations, endotoxemia and cytokine abnormalities as well as the direct effects of alcohol and its metabolites contribute to sarcopenia in ALD. This article focuses on the prevalence, methods to quantify malnutrition, specifically sarcopenia and potential therapies including novel molecular targeted treatments.

Lactate availability is not the major factor limiting muscle glycogen repletion during recovery from an intense sprint in previously active fasted rats

It is not clear whether the amount of accumulated lactate is the main factor limiting muscle glycogen accumulation during recovery from an intense sprint performed by previously active fasted laboratory rats. To address this question, groups of fasted rats swam at moderate intensity for 30 min, each animal with a lead weight equivalent to 0.5% body mass attached to its tail,followed by a 3 min high intensity swim with a 10% lead weight and a recovery period of up to 2 hours afterwards. Moderately intense exercise for 30 min caused a decrease in muscle glycogen levels in the mixed, white and red gastrocnemius and the mixed quadriceps muscles, and a further rapid fall occurred in response to the 3 min sprint effort. During recovery, glycogen increased to comparable or above pre-sprint levels across all muscles, and this occurred to a large extent at the expense of net carbon sources other than lactate, with these carbon sources accounting for at least 36–65%of the glycogen deposited. The sustained dephosphorylation-mediated activation of glycogen synthase, but not the changes in glucose 6-phosphate levels, most probably played an important role in enabling the replenishment of muscle glycogen stores. In conclusion, our findings suggest that the amount of glycogen deposited during recovery from high intensity exercise in fasted animals is not limited by the amount of accumulated lactate.

Carbohydrates and fat for training and recovery

An important goal of the athlete's everyday diet is to provide the muscle with substrates to fuel the training programme that will achieve optimal adaptation for performance enhancements. In reviewing the scientific literature on post-exercise glycogen storage since 1991, the following guidelines for the training diet are proposed. Athletes should aim to achieve carbohydrate intakes to meet the fuel requirements of their training programme and to optimize restoration of muscle glycogen stores between workouts. General recommendations can be provided, preferably in terms of grams of carbohydrate per kilogram of the athlete's body mass, but should be fine-tuned with individual consideration of total energy needs, specific training needs and feedback from training performance. It is valuable to choose nutrient-rich carbohydrate foods and to add other foods to recovery meals and snacks to provide a good source of protein and other nutrients. These nutrients may assist in other recovery processes and, in the case of protein, may promote additional glycogen recovery when carbohydrate intake is suboptimal or when frequent snacking is not possible. When the period between exercise sessions is < 8 h, the athlete should begin carbohydrate intake as soon as practical after the first workout to maximize the effective recovery time between sessions. There may be some advantages in meeting carbohydrate intake targets as a series of snacks during the early recovery phase, but during longer recovery periods (24 h) the athlete should organize the pattern and timing of carbohydrate-rich meals and snacks according to what is practical and comfortable for their individual situation. Carbohydrate-rich foods with a moderate to high glycaemic index provide a readily available source of carbohydrate for muscle glycogen synthesis, and should be the major carbohydrate choices in recovery meals. Although there is new interest in the recovery of intramuscular triglyceride stores between training sessions, there is no evidence that diets which are high in fat and restricted in carbohydrate enhance training.

Effect of alcohol intake on muscle glycogen storage after prolonged exercise

We studied the effects of alcohol intake on postexercise muscle glycogen restoration with samples from vastus lateralis being collected immediately after glycogen-depleting cycling and after a set recovery period. Six well-trained cyclists undertook a study of 8-h recovery (2 meals), and another nine cyclists undertook a separate 24-h protocol (4 meals). In each study, subjects completed three trials in crossover order: control (C) diet [meals providing carbohydrate (CHO) of 1.75 g/kg]; alcohol-displacement (A) diet (1.5 g/kg alcohol displacing CHO energy from C) and alcohol + CHO (AC) diet (C + 1.5 g/kg alcohol). Alcohol intake reduced postmeal glycemia especially in A trial and 24-h study, although insulin responses were maintained. Alcohol intake increased serum triglycerides, particularly in the 24-h study and AC trial. Glycogen storage was decreased in A diets compared with C at 8 h (24.4 +/- 7 vs. 44.6 +/- 6 mmol/kg wet wt, means +/- SE, P < 0.05) and 24 h (68 +/- 5 vs. 82 +/- 5 mmol/kg wet wt, P < 0.05). There was a trend to reduced glycogen storage with AC in 8 h (36.2 +/- 8 mmol/kg wet wt, P = 0.1) but no difference in 24 h (85 +/- 9 mmol/kg wet wt). We conclude that 1). the direct effect of alcohol on postexercise glycogen synthesis is unclear, and 2). the main effect of alcohol intake is indirect, by displacing CHO intake from optimal recovery nutrition practices.

Repeated bouts of high-intensity exercise and muscle glycogen sparing in the rat

Even in the absence of food intake, several animal species recovering from physical activity of high intensity can replenish completely their muscle glycogen stores. In some species of mammals, such as in rats and humans, glycogen repletion is only partial, thus suggesting that a few consecutive bouts of high-intensity exercise might eventually lead to the sustained depletion of their muscle glycogen. In order to test this prediction, groups of rats with a lead weight of 10% body mass attached to their tails were subjected to either one, two or three bouts of high-intensity swimming, each bout being separated from the next by a 1 h re covery period. Although glycogen repletion after the first bout of exercise was only partial, all the glycogen mobilised in subsequent bouts was completely replenished during the corresponding recovery periods and irrespective of muscle fibre compositions. The impact of repeated bouts of high-intensity exercise on plasma levels of fatty acids, acetoacetate and beta-hydroxybutyrate suggests that the metabolic state of the rat prior to the second and third bouts of exercise was different from that before the first bout. In conclusion, rats resemble other vertebrate species in that without food intake there are conditions under which they can replenish completely their muscle glycogen stores from endogenous carbon sources when recovering from high-intensity exercise. It remains to be established, however, whether this capacity is typical of mammals in general.

Glycogen resynthesis in the absence of food ingestion during recovery from moderate or high intensity physical activity: novel insights from rat and human studies

The finding that during recovery from high intensity exercise, rats have the capacity to replenish their muscle glycogen stores even in the absence of food intake has provided us with an experimental model of choice to explore further this process. Our objective here is to share those questions arising from research carried out by others and ourselves on rats and humans that are likely to be of interest to comparative biochemists/physiologists. On the basis of our findings and those of others, it is proposed that across vertebrate species: (1). the capacity of muscles to replenish their glycogen stores from endogenous carbon sources is dependent on the type of physical activity and animal species; (2). lactate and amino acids are the major endogenous carbon sources mobilized for the resynthesis of muscle glycogen during recovery from exercise, their relative contributions depending on the duration of recovery and type of exercise; (3). the relative contributions of lactate glyconeogenesis and hepatic/renal gluconeogenesis to muscle glycogen synthesis is species- and muscle fiber-dependent; and (4). glycogen synthase and phosphorylase play an important role in the control of the rate of glycogen synthesis post-exercise, with the role of glucose transport being species-dependent.

Alcoholic myopathy: biochemical mechanisms

Between one- and two-thirds of all alcohol abusers have impairment of muscle function that may be accompanied by biochemical lesions and/or the presence of a defined myopathy characterised by selective atrophy of Type II fibres. Perturbations in protein metabolism are central to the effects on muscle and account for the reductions in muscle mass and fibre diameter. Ethanol abuse is also associated with abnormalities in carbohydrate (as well as lipid) metabolism in skeletal muscle. Ethanol-mediated insulin resistance is allied with the inhibitory effects of ethanol on insulin-stimulated carbohydrate metabolism. It acutely impairs insulin-stimulated glucose and lipid metabolism, although it is not known whether it has an analogous effect on insulin-stimulated protein synthesis. In alcoholic cirrhosis, insulin resistance occurs with respect to carbohydrate metabolism, although the actions of insulin to suppress protein degradation and stimulate amino acid uptake are unimpaired. In acute alcohol-dosing studies defective rates of protein synthesis occur, particularly in Type II fibre-predominant muscles. The relative amounts of mRNA-encoding contractile proteins do not appear to be adversely affected by chronic alcohol feeding, although subtle changes in muscle protein isoforms may occur. There are also rapid and sustained reductions in total (largely ribosomal) RNA in chronic studies. Loss of RNA appears to be related to increases in the activities of specific muscle RNases in these long-term studies. However, in acute dosing studies (less than 1 day), the reductions in muscle protein synthesis are not due to overt loss of total RNA. These data implicate a role for translational modifications in the initial stages of the myopathy, although changes in transcription and/or protein degradation may also be superimposed. These events have important implications for whole-body metabolism.

Metabolic consequences of alcohol ingestion

Many of the pathophysiological effects of alcohol ingestion relate to the pathways of ethanol metabolism. However, some of the acute and chronic effects of ethanol use are also attributable to the direct effects of ethanol, e.g. on membrane fluidity. Oxidation of ethanol to acetaldehyde is catalysed by alcohol dehydrogenase (ADH). There are at least six classes of ADH, some of which show inter-individual variation, i.e. genetic polymorphism, that influences the rate of ethanol oxidation. A consequence of ethanol oxidation is an increase in the NADH/NAD redox potential within the cytosol and mitochondria with subsequent alteration in several tissue metabolites. The popular hypothesis that most, if not all, of the consequences of chronic alcohol ingestion can be explained by these redox changes is still unproven. This should be considered in the context that most metabolic pathways of the liver are affected by alcohol, as are several endocrine axes in the whole body. In fact most, if not all, tissues and organs are deleteriously affected by chronic ingestion. Acetaldehyde, the product of ethanol oxidation, is chemically highly reactive, toxic and immunogenic. However, the concentrations achieved in vivo usually fall short of those used to produce these toxic effects in experimental situations. Oxidation of acetaldehyde is also coupled to redox changes, although primarily affecting the intra-mitochondrial redox. In addition, further oxidative pathways of ethanol metabolism can lead to the formation of fatty acid ethyl esters, hydroxyethyl free radicals and reactive oxygen species via the ethanol-specific cytochrome P450-2E1 system. There is no conclusive evidence that nutrient supplementation has beneficial effects on overall ethanol-mediated tissue damage.