A further addition to this hypothesis could be that fructose co-ingestion with glucose also provides lactate as an additional fuel source for muscle.
Consistent with this, plasma lactate concentrations are higher with glucose—fructose sucrose ingestion in post-exercise recovery, when compared to glucose alone, in all [ 88 , 90 , 91 , 92 ] but the lowest [ 7 ] carbohydrate ingestion rates.
This raises the question as to whether providing additional substrate for liver glycogen synthesis e. One study has directly compared protein plus sucrose co-ingestion vs.
However, arterial glucose concentrations were lower in the protein—sucrose co-ingestion trial [ 13 ]. It is therefore currently unknown whether the addition of insulinotropic amino acids [that do not delay gastric emptying [ 94 ]] to glucose—fructose sucrose mixtures may augment muscle glycogen re-synthesis at high carbohydrate ingestion rates 1.
Combining amino acids with high ingestion rates of glucose—fructose mixtures could take better advantage of high rates of intestinal absorption and the capacity to deliver exogenous carbohydrate to the circulation in combination with higher insulin availability Figure 2. Whilst current evidence does not indicate that post-exercise muscle glycogen repletion is accelerated by glucose—fructose co-ingestion over glucose alone, this is achieved with lower gastrointestinal issues.
Ingestion of large amounts of carbohydrates is associated with gastrointestinal distress. The ingestion of isocaloric amounts of glucose—fructose or sucrose mixtures, compared to glucose polymers alone, reduces ratings of gastrointestinal distress when large amounts of carbohydrate 1. In contrast to muscle, the liver is able to synthesize glucose in meaningful quantities from 3-carbon precursors such as glucogenic amino acids, galactose, fructose, glycerol, pyruvate and lactate, in addition to the direct pathway involving intact hexose units [ 5 ].
With this in mind, there is potentially a stronger hypothesis for glucose—fructose co-ingestion accelerating liver glycogen repletion over glucose ingestion alone. In addition to higher rates of carbohydrate digestion and absorption, the liver could make use of the ingested fructose for liver glycogen synthesis.
Few studies have directly compared glucose plus fructose sucrose ingestion with glucose polymer ingestion alone, on post-exercise liver glycogen repletion Figure 3 B [ 7 , 90 , 95 ].
Based on the limited number of studies available this does not appear to be dependent on the ingestion rate of glucose Figure 3 B. This may be due to differences in the degree of post-exercise liver glycogen depletion, which appears to be a major driver of liver glycogen synthesis rates [ 5 ].
Furthermore, there is large inter-individual variability in basal liver glycogen concentrations [ 49 ] and therefore it is recommended that within-subject designs are used to clearly establish the dose-response relationship between post-exercise carbohydrate ingestion and liver glycogen repletion.
This effect is clearest when the carbohydrate ingestion rate exceeds 0. Furthermore, the accelerated liver glycogen repletion rate is consistent when glucose and fructose are either co-ingested as their free monomers, or as the disaccharide sucrose Figure 3 B. The majority of these studies again report lower insulinaemia during post-exercise recovery with glucose—fructose co-ingestion vs. It is currently unknown whether the addition of insulinotropic proteins to carbohydrate ingestion can augment post-exercise liver glycogen repletion.
It has been speculated that the co-ingestion of protein and fat could also accelerate liver glycogen repletion by increasing gluconeogenic precursor availability [ 5 ]. Fructose plus glucose ingestion accelerates liver glycogen repletion rates over glucose ingestion alone.
The rapid recovery of both muscle and liver glycogen stores after prolonged exercise are important determinants of the capacity to perform a subsequent bout of moderate- to high- intensity exercise. The repletion of liver and muscle glycogen stores is limited by the systemic availability of carbohydrates and glucogenic precursors, along with insulinaemia, the balance of which varies depending on the scenario.
The rate of appearance of ingested glucose in the circulation appears to be limited by the capacity of intestinal transporters. Since intestinal fructose absorption utilises a different transport mechanism, combining the ingestion of fructose and glucose takes advantage of both transport mechanisms, thereby increasing the total capacity to absorb carbohydrates. However, when sufficient carbohydrate is consumed to maximise muscle glycogen replenishment after exercise, the ingestion of glucose plus fructose sucrose can minimise gastrointestinal distress.
The combined ingestion of glucose plus fructose or sucrose during post-exercise recovery strongly enhances liver glycogen repletion rates, but there is currently insufficient evidence to provide guidelines on the carbohydrate ingestion rates required to specifically maximize liver glycogen repletion.
When ingested in the form of glucose—fructose mixtures or sucrose , not only is this ingestion rate more tolerable due to lower gut discomfort but total body glycogen status can also be enhanced over glucose polymer ingestion alone, due to greater liver glycogen repletion.
National Center for Biotechnology Information , U. Journal List Nutrients v. Published online Mar Javier T. Fuchs , 2 James A. Betts , 1 and Luc J. Cas J. Find articles by Cas J. James A. Luc J. Find articles by Luc J. Author information Article notes Copyright and License information Disclaimer. Received Feb 27; Accepted Mar This article has been cited by other articles in PMC. Abstract Carbohydrate availability in the form of muscle and liver glycogen is an important determinant of performance during prolonged bouts of moderate- to high-intensity exercise.
Keywords: carbohydrates, glycogen, liver, metabolism, muscle, resynthesis, sports nutrition, sucrose. Introduction Carbohydrates are a major substrate for oxidation during almost all exercise intensities [ 1 ]. Dietary Carbohydrates for Sport Nutrition Dietary carbohydrates come in many forms, comprising monosaccharides such as glucose, fructose and galactose; disaccharides such as maltose, sucrose and lactose; and polysaccharides such as maltodextrin and starch Table 1.
Table 1 Common dietary carbohydrates, their constituent monomers and major intestinal transport proteins. Open in a separate window. Endogenous Carbohydrate Stores and Exercise Performance 3. Muscle Glycogen The reintroduction of the muscle biopsy technique to exercise physiology in the s clearly demonstrated the heavy reliance on skeletal muscle glycogen as a fuel source during exercise [ 8 , 38 ].
Liver Glycogen Liver glycogen plays a central role in blood glucose homeostasis during conditions such as exercise, fasting and feeding [ 5 ]. Figure 1. Figure 2. Figure 3. Liver Glycogen Repletion In contrast to muscle, the liver is able to synthesize glucose in meaningful quantities from 3-carbon precursors such as glucogenic amino acids, galactose, fructose, glycerol, pyruvate and lactate, in addition to the direct pathway involving intact hexose units [ 5 ].
Conclusions and Recommendations The rapid recovery of both muscle and liver glycogen stores after prolonged exercise are important determinants of the capacity to perform a subsequent bout of moderate- to high- intensity exercise. Conflicts of Interest The authors declare no conflicts of interest. References 1.
Van Loon L. The effects of increasing exercise intensity on muscle fuel utilisation in humans. Romijn J. Regulation of endogenous fat and carbohydrate metabolism in relation to exercise intensity and duration.
Gonzalez J. Breakfast and exercise contingently affect postprandial metabolism and energy balance in physically active males. Effect of training status on fuel selection during submaximal exercise with glucose ingestion. Liver glycogen metabolism during and after prolonged endurance-type exercise. Stevenson E. Dietary glycemic index influences lipid oxidation but not muscle or liver glycogen oxidation during exercise. Casey A. Effect of carbohydrate ingestion on glycogen resynthesis in human liver and skeletal muscle, measured by 13 c mrs.
Bergstrom J. Diet, muscle glycogen and physical performance. Coyle E. Muscle glycogen utilization during prolonged strenuous exercise when fed carbohydrate.
Alghannam A. Impact of muscle glycogen availability on the capacity for repeated exercise in man. Sports Exerc. Stellingwerff T. Carbohydrate supplementation during prolonged cycling exercise spares muscle glycogen but does not affect intramyocellular lipid use. Sports Exer. Vandenbogaerde T. Effects of acute carbohydrate supplementation on endurance performance: A meta-analysis. Sports Med. Van Hall G. Muscle glycogen resynthesis during recovery from cycle exercise: No effect of additional protein ingestion.
Betts J. Short-term recovery from prolonged exercise: Exploring the potential for protein ingestion to accentuate the benefits of carbohydrate supplements. Burke L. Post-exercise muscle glycogen resynthesis in humans. Rowlands D. Fructose-glucose composite carbohydrates and endurance performance: Critical review and future perspectives.
Muscle glycogen storage after prolonged exercise: Effect of the glycemic index of carbohydrate feedings. Food and Agriculture Organization of the United Nations. The World Health Organization. Fructose is difficult for the liver to process and after a certain point it turns into fat, as well as dampening the metabolism.
Related: Offset your sweet tooth with fish. Glucose is a better fuel, but we can only store so much, so give yourself a top up mid-run. You can rehydrate from shorter sessions by sipping water to avoid the hidden sugars on top of those in your shake.
Related: How much damage will a cheat day do? While high-quality complex carbs whole grains, fruits, and vegetables , should be your go-to sources for carb consumption, you need faster-digesting carbs during and following a workout to maximize performance and recovery. Fast-digesting, simple carbs come in many forms, including cereals, breads, and, yep, candy. During heavy strength-training and HIIT sessions, your body uses blood glucose and stored muscle glycogen to provide a fast-acting source of energy.
When your workout is complete, your body needs to replenish its stores, so eating simple sugars is a fast and effective way to re-up. Something went wrong on our side, please try again. Show references Grant RW, et al. Standards of medical care in diabetes — Diabetes Care. McCulloch DK. Effects of exercise in diabetes mellitus in adults. Accessed Nov. Diabetes diet, eating and physical activity. Physical Activity Guidelines for Americans.
Department of Health and Human Services. Hypoglycemia Low blood glucose. American Diabetes Association. See also Medication-free hypertension control A1C test After a flood, are food and medicines safe to use? Air pollution and exercise Alcohol: Does it affect blood pressure? Artificial sweeteners: Any effect on blood sugar?
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