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

 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.

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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.

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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) 6

Sugar Transport in an Intestinal Epithelial Cell

Intestinal Lumen Enterocyte Blood Glucose Galactose 2 Na Fructose + Apical membrane Glucose Galactose SGLT1 2 Na + Fructose GLUT5 Glucose Galactose Fructose GLUT2 ATP ADP + P i Na + K + Glucose Galactose Fructose Na K + + Basolateral membrane

Abbreviations: ADP, adenosine diphosphate; ATP, adenosine triphosphate; GLUT, glucose transporter; K, potassium; Na, sodium; P i , 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.

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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.

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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.

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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.

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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.

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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.

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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.

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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.

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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.

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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 human studies, the level of fructose ingestion was at least double the current national average intake  In preclinical studies, rodents have much greater ability for de novo lipogenesis from carbohydrates than do humans 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.

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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.

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Review of Carbohydrate Metabolism

The Glycolysis Pathway

Glucose (6 C) Glucokinase (liver) Hexokinase (muscle) a ATP ADP

Glucose-6-phosphate Glycogen Glyceraldehyde-3-phosphate (3C)

NAD Pi NAD + H +

1,3-bisphosphoglycerate

ADP ATP

3-phosphoglycerate Fructose-6-phosphate

Phosphofructokinase ATP ADP

Fructose-1,6-bisphosphate (6 C) Dihydroxyacetone Phosphate (3C) Cytosol Glyceraldehyde-3-phosphate

NAD Pi NAD + H +

1,3-bisphosphoglycerate

ADP ATP

3-phosphoglycerate 2-phosphoglycerate

H 2 0

Phosphoenolpyruvate (PEP)

Pyruvate kinase ADP ATP Pyruvate (3 C)

2-phosphoglycerate

H 2 0

Phosphoenolpyruvate (PEP)

Pyruvate kinase ADP ATP Pyruvate (3 C) a

For clarity, only selected enzymes are shown. Abbreviations: ADP, adenosine di phosphate; ATP, adenosine triphosphate; C, carbon; NAD, nicotinamide adenine dinucleotide; P i , phosphate group.

Berg JM, et al. Biochemistry. 5th ed. New York, NY: WH Freeman & Co.; 2002.

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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. 20

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.

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Entry of Glucose, Galactose, and Fructose Into Liver Glycolysis

Glucose

ATP ADP

Galactose Galactokinase

ATP Galactose-1-phosphate ADP

UDP-glucose: Galactose-1-phosphate uridyl transferase

UDP-glucose Glucose-1-phosphate

Fructose

Glucose-6-phosphate

Fructokinase

Fructose-1-phosphate Fructose-6-phosphate

Phosphofructokinase

Fructose-1,6-bisphosphate

Aldolase

ATP ADP Glyceraldehyde + Dihydroxyacetone phosphate Glyceraldehyde-3-phosphate + Dihydroxyacetone phosphate UDP-galactose

UDP-glucose-4-epimerase

Abbreviations: ADP, adenosine diphosphate; ATP, adenosine triphosphate; UDP, uridine diphosphate.

Berg JM, et al. Biochemistry. 5th ed. New York, NY: WH Freeman & Co.; 2002.

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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.

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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.

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Gluconeogenesis in Liver

Reactions different than glycolysis Glucose P i Glucose-6-phosphatase Glucose-6-phosphate Fructose-6-phosphate Pi Fructose-1,6-bisphosphatase Fructose-1,6-bisphosphate Dihydroxyacetone-phosphate Glycerol-3-phosphate Glycerol Amino acids Glycerol-3-phosphate TCA cycle Phosphoenolpyruvate (PEP) Phosphoenolpyruvate carboxykinase (PEPCK) Amino acids oxaloacetate Alanine Pyruvate carboxylase Pyruvate Lactate Abbreviations: TCA, tricarboxylic acid; P i , phosphate group.

Berg JM, et al. Biochemistry. 5th ed. New York, NY: WH Freeman & Co.; 2002.

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The Cori (Lactate) and Glucose-Alanine Cycles

Liver Blood Muscle

Glucose Glucose-6-phosphate Glycogen Urea Pyruvate Lactate NH 2 Lactate Pyruvate Alanine Alanine Glycogen Glucose-6-phosphate Lactate Pyruvate Alanine NH 2 (eg, from leucine) Abbreviation: NH 2 , amino functional group.

Berg JM, et al. Biochemistry. 5th ed. New York, NY: WH Freeman & Co.; 2002.

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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  Debranching enzyme 4 and 1  6 glucosidase (acid maltase) • • • Muscle phosphorylase Liver phosphorylase Others Berg JM, et al. Biochemistry. 5th ed. New York, NY: WH Freeman & Co.; 2002.

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Glycogenesis/Glycogenolysis in Liver and Muscle

UDP  -1,4 glucose units Glycogen synthase Branching enzyme Glycogen (  -1,4 and  -1,6 glucose units) Glycogen phosphorylase P i Glycogen primer + UDP-glucose PP i UDP Glucose-1-phosphate ATP ADP Glucose-6-phosphate Glucose-6-phosphatase (liver only) Glucokinase (liver) Hexokinase (muscle) Glucose Glucan transferase/ debranching enzyme Free glucose Abbreviations: ADP, adenosine diphosphate; ATP, adenosine triphosphate; P i , phosphate group; PP i , pyrophosphate; UDP, uridine diphosphate.

Berg JM, et al. Biochemistry. 5th ed. New York, NY: WH Freeman & Co.; 2002.

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Carbohydrates: Glycogen Storage

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.

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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 Trained, normal diet 80 to 90 mmol/kg muscle (wet weight) 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. 31

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.

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Muscle Glycogen Storage—Effects of Exercise

2.5

2.0

1.5

1.0

0.5

KS PT RB RG DC Average (N = 4) PRE 10 miles POST Day 1 PRE 10 miles POST Day 2 PRE 10 miles POST Day 3 5 TH DAY POST

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.

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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.

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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 70 60 50 ± SE a 40 30 20 10 0 7 meals 2 meals 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.

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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 36

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 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). Significantly faster compared with CHO (

P

< .05). Abbreviations: CHO, carbohydrate; Pro, protein.

Zawadzki KM, et al. J Appl Physiol. 1992:72(5):1854-1859.

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Effects of Carbohydrate-Protein Combination on Muscle Glycogen Storage During Recovery

60 50 40 30 a 120-240 min 40-120 min 0-40 min 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

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 a Significantly higher compared with HCHO (

P

= .013) and LCHO ( Reprinted from Ivy JL, et al. J Appl Physiol. 2002;93(4):1337-1344.

P

= .004). Abbreviations: CHO, carbohydrate; Pro, protein; HCHO, high carbohydrate; LCHO, low carbohydrate.

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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

P RE -E XE P OST -E XE P OST -E XE Subject 1 Diet Day 1 9 AM Immediate 5 PM Day 2 9 AM 5 PM Fasting F+P Day 3 9 AM F+P Day 4 9 AM F+P Day 5 9 AM F+P Day 6 F+P Day 7 9 AM 5 PM CHO Day 8 9 AM Day 9 9 AM MG 1.66 0.01 0.36

0.43

0.61

0.63

0.76

0.70

1.02

1.61

Subject 2 Diet Fasting F+P F+P F+P F+P F+P F+P CHO MG 1.24

0.01

0.20

0.22

0.24

0.47

0.91

1.10

2.11

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.

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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.

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Timing of Postexercise Carbohydrate Ingestion and Glycogen Resynthesis

(continued) Immediate feeding Delayed feeding (2 hours) 2 P < .05

8 NS 4 P < .05

20 40 Muscle Glycogen Storage, mmol/kg wet weight 1

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.

24 50 100 Muscle Glycogen Storage, mmol/kg wet weight 2 NS

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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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