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Carbohydrates in Exercise and Recovery

Carbohydrates in Exercise and Recovery. Advanced Level. Module I. Carbohydrates: Definitions, Digestion, and Absorption Review of Carbohydrate Metabolism Carbohydrates: Glycogen Storage. Carbohydrates: Definitions, Digestion, and Absorption . Importance of Carbohydrates in Sports Nutrition.

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Carbohydrates in Exercise and Recovery

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  1. Carbohydrates in Exercise and Recovery Advanced Level

  2. Module I Carbohydrates: Definitions, Digestion, and Absorption Review of Carbohydrate Metabolism Carbohydrates: Glycogen Storage

  3. Carbohydrates: Definitions, Digestion, and Absorption

  4. Importance of Carbohydrates in Sports Nutrition • Carbohydrates are a major fuel source for exercising muscle, especially as exercise intensity and duration increase • Types of carbohydrate oxidation • Exogenous: Oxidizing carbohydrates ingested from the diet • Endogenous: Breaking down stored carbohydrate (ie, glycogen) for energy needs • Carbohydrates can also influence fluid absorption from the intestine (hydration) • Some carbohydrates can cause gastrointestinal intolerance and could impair performance for that reason United States Anti-doping Agency. Optimal dietary intake guide. Available at: http://www.usada.org/diet/?gclid=COOM-Ky95aYCFQTNKgodzVQL2w. Accessed January 31, 2011.

  5. Carbohydrate Digestion and Absorption • Carbohydrates are found in the diet as • Free monosaccharide (1 sugar unit) or • Larger saccharides (chains of monosaccharides) • Enzymes must digest larger saccharides down to individual monosaccharides before these monosaccharides can be absorbed • Carbohydrates that escape absorption make their way to the colon (variable degrees of bacterial fermentation) • Monosaccharides are absorbed from the intestine mainly via active transport (energy-requiring) or facilitated diffusion • Both active transport and facilitated diffusion require transporters • SGLT (Active transport) • GLUT (Facilitated diffusion) Abbreviations: SGLT, sodium-glucose linked transporter; GLUT, glucose transporter. Holmes R. J Clin Pathol. 1971;S3-5:10-13. doi:10.1136/jcp.s3-5.1.10.

  6. Why Do We Need to Know About Carbohydrate Absorption in Sports Nutrition? • The ability of the intestine to absorb a carbohydrate can be the rate-limiting step for its delivery to muscle cells for fuel use • Intestinal sugar transporters can become saturated, resulting in malabsorption of a carbohydrate • Concept of multiple transportable carbohydrates • Use a blend of sugars that require different transporter systems • May increase carbohydrate absorption relative to using just a single sugar • Enzyme systems in the intestine may be insufficient to digest some carbohydrates (eg, lactose intolerance)

  7. Sugar Transport in an Intestinal Epithelial Cell Intestinal Lumen Enterocyte Blood Glucose Galactose Fructose Glucose Galactose Fructose Glucose Galactose Glucose Galactose SGLT1 GLUT2 2 Na+ 2 Na+ Na+ Na+ ATP Fructose Fructose ADP + Pi GLUT5 K+ K+ Apical membrane Basolateral membrane Abbreviations: ADP, adenosine diphosphate; ATP, adenosine triphosphate; GLUT, glucose transporter; K, potassium; Na, sodium; Pi, phosphate group; SGLT, sodium-glucose linked transporter.Scheepers A, et al. JPEN J of Parenter Enteral Nutr. 2004;28(5):364-371.Drozdowski LA, et al. World J Gastroenterol. 2006;12(11):1657-1670.

  8. Major Dietary Monosaccharides No Digestion Required for Absorption • Glucose; from corn and other plants • Also called dextrose • Absorbed primarily by active transport (SGLT1), with facilitated diffusion (GLUT2) used to a lesser extent when intraluminal glucose concentrations are high • SGLT1 requires sodium co-transport and ATP • Transported out of enterocyte via GLUT2 • Muscles express GLUT4 transporters to take up glucose from the blood • Fructose; fruit sugar • Absorbed by facilitated diffusion (primarily GLUT5) • Simultaneous presence of glucose stimulates fructose uptake, probably by GLUT2 • Transported out of enterocyte via GLUT2 • Fructose is taken up almost entirely by the liver; very little circulates in the blood • Galactose • Is a component of lactose (milk sugar) • Is transported from the intestine similarly to glucose • Converted to glucose in the liver Abbreviations: ATP, adenosine triphosphate; SGLT, sodium-glucose linked transporter; GLUT, glucose transporter.McGrane MM. Carbohydrate metabolism—synthesis and oxidation. In: Stipanuk M. Biochemical, Physiological & Molecular Aspects of Human Nutrition. 2nd Edition. Saunders/Elsevier; 2006: chap 12.

  9. Common Dietary Disaccharides • Sucrose (table sugar) • Extracted from sugar cane and beets • Composed of glucose and fructose (alpha-1,2 linked) • Digested by sucrase-isomaltase complex • Anchored in brush border of small intestine • Lactose • Primary sugar in virtually all mammalian milks • Composed of glucose and galactose (beta-1,4 linked) • Digested by brush border lactase-phlorizin hydrolase Hertzler SR, et al. Intestinal disaccharidase depletions. In: Shils ME, et al. Modern Nutrition in Health and Disease. 10th Edition. Baltimore, MD: Lippincott Williams & Wilkins; 2006: pp 1189-1200.

  10. Common Dietary Disaccharides (continued) • Maltose • Found in some fermented beverages (eg, beer) and is also an intermediate product in starch digestion • Composed of 2 glucose molecules (alpha-1,4 linked) • Digested by maltase-glucoamylase • Trehalose • Found in mushrooms • Composed of 2 glucose molecules (alpha-1,1 linked) • Digested by trehalase Hertzler SR, et al. Intestinal disaccharidase depletions. In: Shils ME, et al. Modern Nutrition in Health and Disease. 10th Edition. Baltimore, MD: Lippincott Williams & Wilkins; 2006: pp 1189-1200.

  11. Oligosaccharides (3-10 Monosaccharide Units) • Oligosaccharides are found in human milk and in a variety of fruits and vegetables • Many of these are not digestible by human enzymes • Examples • Stachyose (galactose-glucose-fructose) • Raffinose (galactose-galactose-glucose-fructose) • Fructooligosaccharides and oligofructose • Chains of fructose units sometimes terminated with glucose • Glucose polymers/maltodextrins • Most are rapidly digestible; some are resistant to digestion Carbohydrates. In: Gropper SS, et al. Advanced Nutrition and Human Metabolism. 4th Edition. Belmont, CA: Wadsworth, Cengage Learning.; 2005: pp 63-106.

  12. Digestible Polysaccharides • Plant starches (digestion via salivary and pancreatic amylases) • Amylopectin • Chains of alpha-1,4 linked glucose with alpha-1,6 branch points (renders the starch more digestible) • Amylose • Straight chains of glucose linked by alpha-1,4 bonds • Less digestible than amylopectin • Animal starch • Glycogen • Storage form of glucose in liver and muscles • Similar in structure to amylopectin, but more highly branched Carbohydrates. In: Gropper SS, et al. Advanced Nutrition and Human Metabolism. 4th Edition. Belmont, CA: Wadsworth, Cengage Learning.; 2005: pp 63-106.

  13. Nondigestible Polysaccharides (Dietary Fibers) • Cellulose • Chain of glucose units linked by beta-1,4 bonds • Hemicelluloses • Pectins • Gums • Mucilages • Some indigestible oligosaccharides would count as dietary fibers Carbohydrates. In: Gropper SS, et al. Advanced Nutrition and Human Metabolism. 4th Edition. Belmont, CA: Wadsworth, Cengage Learning.; 2005: pp 63-106.

  14. What Is High-Fructose Corn Syrup? • Cornstarch converted to a syrup that is essentially 100% dextrose (glucose) • Enzymes isomerize dextrose to produce 42% fructose syrup (HFCS-42) • Refiners draw HFCS-42 through an ion exchange column that retains fructose • Result is HFCS-90 syrup • The HFCS-90 syrup is blended with HFCS-42 • Result is HFCS-55 • The HFCS-55 syrup is the type used mainly in beverage industry • Syrup is 55% fructose, 45% dextrose • Essentially no different than sucrose (table sugar; 50% fructose, 50% glucose) • The term “high-fructose corn syrup” is a little misleading • Because corn syrup is 100% glucose, any presence of fructose typically results in it being labeled “high-fructose corn syrup” Soenen S, et al. Am J Clin Nutr. 2007;86(6):1586-1594.Smith JS, et al. Food Processing: Principles and Applications. Ames, IA: Blackwell Publishing; 2004, p 212-214.

  15. What Is the Potential Concern Regarding High-Fructose Corn Syrup? • Animal and human studies using large amounts of fructose (generally > 17% of total energy), relative to the same amount of glucose, show • Increases in blood triglyceride levels • Decreased insulin sensitivity • Possible increases in visceral adiposity • Potential explanations • Unregulated metabolism of fructose increases de novo lipogenesis • Fructose, unlike glucose, does not generate an insulin response • Insulin may directly lower food intake • Insulin may increase leptin release from adipose tissue (leptin decreases food intake) Bantle JP, et al. Am J Clin Nutr. 2000;72(5):1128-1134. Stanhope KL, et al. J Clin Invest. 2009;119(5):1322-1334.

  16. Keys to Making Sense of Fructose or High-Fructose Corn Syrup Literature • Pure fructose versus high-fructose corn syrup is an important issue • Human studies have generally used pure fructose, not high-fructose corn syrup or sucrose • In preclinical studies, rodents have much greater ability for de novo lipogenesis from carbohydrates than do humans • In human studies, the level of fructose ingestion was at least double the current national average intake • Sex differences • Men are more susceptible than women to the effects of fructose in blood lipids (ie, triglycerides) DiMeglio DP, et al. Int J Obesity. 2000;24:794-800; Melanson KJ, et al. Nutrition. 2007;23(2):103-112; Stanhope KL, et al. Am J Clin Nutr. 2008;87(5):1194-1203; Soenen S, et al. Am J Clin Nutr. 2007;86(6):1586-1594.

  17. The Truth About High-Fructose Corn Syrup • Too much sugar, of any kind, in beverages is not recommended • Poor compensation for carbohydrate energy consumed in beverages can lead to weight gain • However, there are no differences in metabolic responses to high-fructose corn syrup and sucrose in humans • No differences in circulating hormones • No differences in appetite or satiety-related variables DiMeglio DP, et al. Int J Obesity. 2000;24:794-800; Melanson KJ, et al. Nutrition. 2007;23(2):103-112; Stanhope KL, et al. Am J Clin Nutr. 2008;87(5):1194-1203; Soenen S, et al. Am J Clin Nutr. 2007;86(6):1586-1594.

  18. Review of Carbohydrate Metabolism

  19. The Glycolysis Pathway Glucose (6 C) ATP Glucokinase (liver) Hexokinase (muscle)a Glycogen ADP Glucose-6-phosphate Cytosol Fructose-6-phosphate ATP Phosphofructokinase ADP Fructose-1,6-bisphosphate (6 C) Glyceraldehyde-3-phosphate (3C) Dihydroxyacetone Phosphate (3C) Glyceraldehyde-3-phosphate NAD NAD Pi Pi NAD + H+ NAD + H+ 1,3-bisphosphoglycerate 1,3-bisphosphoglycerate ADP ADP ATP ATP 3-phosphoglycerate 3-phosphoglycerate 2-phosphoglycerate 2-phosphoglycerate H20 H20 Phosphoenolpyruvate (PEP) Phosphoenolpyruvate (PEP) ADP ADP Pyruvate kinase Pyruvate kinase ATP ATP Pyruvate (3 C) Pyruvate (3 C) aFor clarity, only selected enzymes are shown. Abbreviations: ADP, adenosine di phosphate; ATP, adenosine triphosphate; C, carbon; NAD, nicotinamide adenine dinucleotide; Pi, phosphate group.Berg JM, et al. Biochemistry. 5th ed. New York, NY: WH Freeman & Co.; 2002.

  20. Galactose and Glycolysis • Galactose (Gal) • Phosphorylated to galactose-1-phosphate (Gal-1-P) by galactokinase • Gal-1-P converted to glucose-1-phosphate (Glc-1-P) • Gal-1-P uridyl transferase • Uridine diphosphogalactose 4-epimerase • Glc-1-P then enters glycolysis as does glucose derived from glycogen • Inborn errors of metabolism • Can have inborn defects of the 3 enzymes of Gal metabolism (galactosemia) • Results in accumulation of Gal in tissues such as lens of eye and damage (cataracts) due to osmotic effect • Gal-free diet required • Effect of ethanol • Inhibits the epimerase enzyme Abbreviation: Glc, glucose. Berg JM, et al. Biochemistry. 5th ed. New York, NY: WH Freeman & Co.; 2002. Badawy AA-B. Alcohol and Alcoholism. 1977;12(3):120-136.

  21. Fructose and Glycolysis • Fructose • Most is taken up by the liver and phosphorylated to fructose 1-phosphate (F-1-P) by fructokinase • Aldolase B (liver form) splits F-1-P into glyceraldehyde and DHAP • Both can become glyceraldehyde-3-P (part of glycolytic pathway) • Important that this enters glycolysis past PFK regulatory step • Inborn errors of metabolism • Fructokinase defect (fructosuria) • Not serious • Aldolase B defect • Accumulation of F-1-P • Depletion of cellular phosphate stores • Blocking of glycogen breakdown and gluconeogenesis • Fructose-free diet required Abbreviations: DHAP, dihydroxyacetone phosphate; PFK, phosphofructokinase. Berg JM, et al. Biochemistry. 5th ed. New York, NY: WH Freeman & Co.; 2002. Steinmann B, et al. Disorders of fructose metabolism. In: Scriver CR, Beaudet AL, Sly WS, Eds. The Metabolic and Molecular Bases of Inherited Disease. 8th ed. New York; McGraw Hill; 2001, p 1489-1520.

  22. Entry of Glucose, Galactose, and Fructose Into Liver Glycolysis Galactose ATP Galactokinase ADP Galactose-1-phosphate UDP-glucose: Galactose-1-phosphate uridyl transferase UDP-glucose Glucose ATP ADP UDP-galactose UDP-glucose-4-epimerase Glucose-1-phosphate Glucose-6-phosphate Fructose Fructose-6-phosphate Fructokinase Phosphofructokinase Fructose-1,6-bisphosphate Fructose-1-phosphate Aldolase Glyceraldehyde-3-phosphate ADP ATP + Glyceraldehyde Dihydroxyacetone phosphate + Dihydroxyacetone phosphate Abbreviations: ADP, adenosine diphosphate; ATP, adenosine triphosphate; UDP, uridine diphosphate. Berg JM, et al. Biochemistry. 5th ed. New York, NY: WH Freeman & Co.; 2002.

  23. Pentose Phosphate Pathway, or Hexose Monophosphate Shunt • Alternative liver pathway for utilizing glucose • Can be used to generate ribose for nucleotide and ATP synthesis • Can also serve as a source of NADPH for oxidation-reduction (redox) reactions • Example: reduction of glutathione to maintain stability of RBC membrane Abbreviations: ATP, adenosine triphosphate; NADPH, nicotinamide adenine dinucleotide phosphate; RBC, red blood cell. Berg JM, et al. Biochemistry. 5th ed. New York, NY: WH Freeman & Co.; 2002.

  24. Gluconeogenesis • Almost a reversal of glycolysis, but must overcome thermodynamic barriers for 3 reactions: • Glucokinase/hexokinase • Phosphofructokinase • Pyruvate kinase • Methods of circumvention: • Glucose-6-phosphatase • Fructose 1,6-bisphosphatase • Pyruvate carboxylase and phosphoenolpyruvate carboxykinase (PEPCK) • Pyruvate carboxylase requires biotin as coenzyme Berg JM, et al. Biochemistry. 5th ed. New York, NY: WH Freeman & Co.; 2002.

  25. Gluconeogenesis in Liver Glucose Reactions different than glycolysis Pi Glucose-6-phosphatase Glucose-6-phosphate Fructose-6-phosphate Pi Fructose-1,6-bisphosphatase Fructose-1,6-bisphosphate Dihydroxyacetone-phosphate Glycerol-3-phosphate Glycerol-3-phosphate Glycerol Phosphoenolpyruvate (PEP) Phosphoenolpyruvate carboxykinase (PEPCK) Amino acids TCA cycle oxaloacetate Amino acids Alanine Pyruvate carboxylase Pyruvate Lactate Abbreviations: TCA, tricarboxylic acid; Pi, phosphate group. Berg JM, et al. Biochemistry. 5th ed. New York, NY: WH Freeman & Co.; 2002.

  26. The Cori (Lactate) and Glucose-Alanine Cycles Blood Liver Muscle Glucose Glucose-6-phosphate Glycogen Glycogen Glucose-6-phosphate Urea Lactate Pyruvate Lactate Lactate Pyruvate NH2 (eg, from leucine) Pyruvate NH2 Alanine Alanine Alanine Abbreviation: NH2, amino functional group. Berg JM, et al. Biochemistry. 5th ed. New York, NY: WH Freeman & Co.; 2002.

  27. Glycogen • Glycogen is degraded by a different pathway than its synthesis • Key enzyme for degradation is the activation of glycogen phosphorylase • Vitamin B6 (pyridoxal phosphate) is a structural part of glycogen phosphorylase • Several types of glycogen storage disorders • Deficiencies of • Glucose-6-phosphatase • Lysosomal alpha 1  4 and 1  6 glucosidase (acid maltase) • Debranching enzyme • Muscle phosphorylase • Liver phosphorylase • Others Berg JM, et al. Biochemistry. 5th ed. New York, NY: WH Freeman & Co.; 2002.

  28. Glycogenesis/Glycogenolysis in Liver and Muscle Glycogen (-1,4 and -1,6 glucose units) Branching enzyme -1,4 glucose units UDP Glycogen phosphorylase Pi Glycogen synthase Glycogen primer + UDP-glucose Glucan transferase/ debranching enzyme PPi UDP Glucose-1-phosphate ATP ADP Glucose-6-phosphate Free glucose Glucose-6-phosphatase (liver only) Glucokinase (liver) Hexokinase (muscle) Glucose Abbreviations: ADP, adenosine diphosphate; ATP, adenosine triphosphate; Pi, phosphate group; PPi, pyrophosphate; UDP, uridine diphosphate. Berg JM, et al. Biochemistry. 5th ed. New York, NY: WH Freeman & Co.; 2002.

  29. Carbohydrates: Glycogen Storage

  30. Storage of Carbohydrate in the Body • Glucose that is absorbed, but not immediately needed, is stored as glycogen • Found in the liver and skeletal muscles • It is similar to starch • Glycogen in liver is a reserve glucose supply to the brain • Glycogen in muscles is an energy source for exercise • Glycogen synthase in muscles is at peak activity immediately following glycogen-depleting exercise • Eat carbohydrates immediately after exercise for most rapid glycogen replenishment United States Anti-doping Agency. Optimal dietary intake guide. Available at: http://www.usada.org/diet/?gclid=COOM-Ky95aYCFQTNKgodzVQL2w. Accessed January 31, 2011. Berg JM, et al. Biochemistry. 5th ed. New York, NY: WH Freeman and Co.; 2002.

  31. Glycogen Distribution in the Body • Liver • 60 to 120 g (4% to 8% of liver weight, overnight fasting versus fed, respectively) • Liver glycogen is generally quite depleted by overnight fasting • Skeletal muscle • 200 to 500 g (highly variable) • Effects of training and carbohydrate loading on muscle glycogen stores • Untrained, normal diet 80 to 90 mmol/kg muscle (wet weight) • Trained, normal diet 130 to 135 mmol/kg muscle (wet weight) • Trained, carbohydrate-loaded 210 to 230 mmol/kg muscle (wet weight) Coleman E. Today’s Dietitian. March 2002:15-18. Flatt JP. Am J Clin Nutr. 1995;61(suppl):952S-959S.

  32. Glycogen Terminology • Terms related to glycogen synthesis • Glycogen synthase (enzyme that forms glycogen) • Glycogenin (primer for glycogen synthesis) • Proglycogen • Initial phase of glycogen synthesis (glycogenin + small number of glucose molecules) • Macroglycogen • Larger ratio of glucose molecules to glycogenin • Forms to a greater extent vs proglycogen after 2 to 3 days of high-carbohydrate diet • Terms related to glycogen breakdown • Glycogen phosphorylase • Breaks down glycogen, with ultimate formation of glucose-6-phosphate • Glucose-6-phosphatase • Necessary to release the glucose from cell into blood • Enzyme is present in liver, absent in skeletal muscle • Muscle glycogen for local use only Berg JM, et al. Biochemistry. 5th ed. New York, NY: WH Freeman and Co.; 2002. Huang M, et al. J Clin Invest. 1997;99(3):501–505. doi:10.1172/JCI119185.

  33. Muscle Glycogen Storage—Effects of Exercise KS PT RB RG DC Average (N = 4) 2.5 2.0 1.5 Muscle Glycogen, g/100 g tissue 1.0 0.5 PRE POST PRE POST PRE POST 5TH DAYPOST Day 1 Day 2 Day 3 10 miles 10 miles 10 miles Diet: carbohydrate, 40% to 50% kcals; fat, 30% to 40% kcals; protein, 10% to 15% kcals. Costill DL, et al. J Appl Physiol. 1971;31(6):834-838.

  34. Factors Influencing Muscle Glycogen Synthesis • Energy and CHO availability • Timing of meals relative to completion of exercise(sooner the better) • Additional protein possibly • GI of CHO (higher GI = faster) • Degree to which glycogen is depleted (more depletion = faster) • Rest (tapering of exercise is necessary) • Sex • Men and women respond equally (ie, glycogen storage) if energy and CHO are adequate • Women seem to be less reliant on CHO and more reliant on fat during exercise than men Abbreviations: CHO, carbohydrate; GI, glycemic index.

  35. Muscle Glycogen Storage—Effects of Diets With Differing CHO Levels • Simple and complex CHO had equal glycogen resynthesis within the first 24 hours postexercise • Complex CHO had somewhat greater glycogen synthesis during subsequent 24 hours 80 a 70 ± SE 60 50 Change in Muscle Glycogen(mmol/kg muscle/24 hr) 40 30 20 7meals 2meals 10 0 25% 50% 70% 70% CHO diets, % of calories • Runners performed glycogen-depleting exercise before dietary intake • Diets differed in percent of kcals from CHO, CHO type, and number of meals Abbreviations: CHO, carbohydrate; SE, standard error.a Significant difference between the mean and the mean change in muscle glycogen observed during the mixed diet (50% of cal from CHO). Reprinted from Costill DL, et al. Am J Clin Nutr. 1981;34(9):1831-1836.

  36. Can Protein Boost the Rate of Glycogen Storage? • Mixed results in clinical studies • Yes • Zawadski KM, et al. J Appl Physiol. 1992;72:1854-1859 • Ivy JL, et al. J Appl Physiol. 2002;93:1337-1344 • No • Roy BD, et al. J Appl Physiol. 1997;83:1877-1883 • Jentjens RL, et al. J Appl Physiol. 2001;91:839-846. • Van Hall G, et al. J Appl Physiol. 2000;88:1631-1636. • Key issues • More frequent feeding intervals did not show benefit with protein • Adequacy of carbohydrate and protein intake • Protein may be more important if athlete is unable to consume enough carbohydrate

  37. Effect of Carbohydrate and Protein on Muscle Glycogen During Recovery a,b 40 112 g CHO, 41 g protein 112 g CHO 41 g protein 30 a Muscle Glycogen Storage Rate, µmol/g pro/hour 20 10 0 CHO-PRO CHO PRO • Subjects ingested diet immediately and 2 hours after glycogen-depleting exercise; glycogen storage was assessed immediately and 4 hours postexercise a Significantly faster compared with PRO (P < .05). b Significantly faster compared with CHO (P < .05).Abbreviations: CHO, carbohydrate; Pro, protein. Zawadzki KM, et al. J Appl Physiol. 1992:72(5):1854-1859.

  38. Effects of Carbohydrate-Protein Combination on Muscle Glycogen Storage During Recovery CHO-Pro: 80 g CHO, 28 g protein, 6 g fat HCHO: 108 g CHO, 6 g fat LCHO: 80 g CHO, 6 g fat 120-240 min 60 40-120 min a 50 0-40 min 40 30 Muscle Glycogen Storage, mmol/L 20 10 0 CHO-PRO HCHO LCHO • Subjects ingested diet immediately and 2 hours after glycogen-depleting exercise; glycogen storage was assessed immediately, at 20 and 40 minutes, and at 1, 2, 3, and 4 hours postexercise aSignificantlyhigher compared with HCHO (P = .013) and LCHO (P = .004). Abbreviations: CHO, carbohydrate; Pro, protein; HCHO, high carbohydrate; LCHO, low carbohydrate.Reprinted from Ivy JL, et al. J Appl Physiol. 2002;93(4):1337-1344.

  39. Muscle Glycogen Resynthesis With Different Diets After Exercise • A diet of fat plus protein following exercise was not able to restore pre-exercise levels of muscle glycogen up to 4 days later • However, a carbohydrate diet restored muscle glycogen within 2 days Abbreviations: Exe, exercise; MG, muscle glycogen (g/100 g wet muscle tissue); F+P, 2000 kcal from fat and protein (<5% carbohydrate); CHO, 2000 kcal from carbohydrate ( 95% carbohydrate). Hultman E and Bergström J. Acta Med Scand. 1967;182(1):109-117.

  40. Timing of Postexercise Carbohydrate Ingestion and Glycogen Resynthesis • Maximal glycogen synthase is within 2 hours of exercise • “Window of opportunity” to promote faster glycogen repletion • Glycogen synthesis at 2 hours postexercise: more rapid with carbohydrate ingestion immediately postexercise vs carbohydrate ingestion delayed 2 hours postexercise • However, the delayed ingestion group can catch up within 24 hours given adequate carbohydrate intake • Key advantage of carbohydrate ingestion immediately postexercise is for athletes with multiple events in a short time span • Need fast glycogen recovery Ivy JL, et al. J Appl Physiol. 1988;64(4):1480-1485.Parkin JA, et al. Med Sci Sports Exerc. 1997;29(2):220-224. Burke LM, et al. J Sports Sci. 2004;22:15-30.

  41. Timing of Postexercise Carbohydrate Ingestion and Glycogen Resynthesis (continued) Immediate feeding Delayed feeding (2 hours) NS P < .05 2 8 Time Postexercise, hours Time Postexercise, hours NS 4 24 P < .05 20 40 50 100 Muscle Glycogen Storage,mmol/kg wet weight1 Muscle Glycogen Storage,mmol/kg wet weight2 1. Ivy JL, et al. J Appl Physiol. 1988;64(4):1480-1485.2. Parkin JA, et al. Med Sci Sports Exerc. 1997;29(2):220-224.

  42. Summary of Key Messages • Carbohydrates are the major energy source for exercising muscle • The type of carbohydrate consumed influences the availability of energy to the muscle • Absorption and digestion are key steps • Excess carbohydrates in the body can be stored as glycogen for later muscle use • A high-carbohydrate diet helps to maximize glycogen stores and generally increases exercise performance • Postexercise meal content and timing can optimize glycogen resynthesis

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