Carbohydrates
in Exercise and Recovery
Rookie version
Outline
I. Carbohydrates: Definitions,
digestion, absorption
A. Carbohydrates in the diet
B. Digestion and absorption
of carbohydrates
C. Carbohydrate metabolism
D. Glycogen—storage of
carbohydrates in the body
II. Properties of carbohydrates:
Considerations for sports
performance
A. Glycemic index
B. Glycemic load
C. High-fructose corn syrup
III. Training
A. Carbohydrates before exercise
B. Carbohydrates during exercise
C. Recovery
D. Meal planning
IV. Competition
A. Carbohydrate loading
B. Pre-competition meals
C. Carbohydrates during competition
I. Carbohydrates:
Definitions, Digestion, Absorption, and Storage
Carbohydrates in Sports Nutrition
 Carbohydrates (CHOs) are a major fuel source for exercising
muscle, especially in high-intensity or long-duration activities
 Carbohydrates can influence fluid absorption from the intestine
(hydration)
 Some CHOs can cause gastrointestinal intolerance and thereby
impair exercise performance
 Types of CHOs
– Exogenous: CHO intake from the diet
– Endogenous: CHO stored in the body (ie, glycogen) that can be used for
energy needs
 Glycogen is stored glucose in the body
– It is a network of glucose molecules connected together, similar to starch
United States Anti-doping Agency. Optimal dietary intake guide. Available at:
http://www.usada.org/diet/?gclid=COOM-Ky95aYCFQTNKgodzVQL2w. Accessed January 31, 2011.
Carbohydrates in Diet
Carbohydrates are found in the diet as
1. Free monosaccharides (1 sugar unit)
• Glucose (aka dextrose, from corn and other plants)
• Fructose (from fruit)
• Galactose (from milk)
2. Di-, tri-, oligo- (4 to 10 units), or polysaccharides (chain of 11+ monosaccharides)
• Sucrose (disaccharide of glucose + fructose)
• Lactose (disaccharide of glucose + galactose)
• Maltose (disaccharide of 2 glucose molecules)
• Trehalose (disaccharide of 2 glucose molecules,
with a different linkage between the two)
• Starch (polysaccharide of glucose)
Berg JM, et al. Biochemistry. 5th ed. New York, NY: WH Freeman and Co; 2002.
Carbohydrate Digestion
 Carbohydrates are absorbed as monosaccharides
 Enzymes must digest di-, tri-, oligo-, and polysaccharides into
individual monosaccharides
– Enzymes exist in the saliva, stomach, and small intestine to break the
different linkages between the various sugars
 There are special transporters in the cell membranes of intestinal
cells that selectively absorb monosaccharides
– Monosaccharides are then transported into the blood stream, where they
are distributed throughout the body
 Carbohydrates that escape digestion and absorption make their
way to the colon (with variable degrees of bacterial fermentation)
Holmes R. J Clin Pathol. 1971;5(suppl):10-13.
Why Is Carbohydrate Absorption Important
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
 Enzyme systems in the intestine may be insufficient to digest
some carbohydrates (eg, lactose intolerance)
 Intestinal sugar transporters can become saturated, resulting in
malabsorption of a carbohydrate
 There are multiple transporters for carbohydrates
– Ingest a blend of sugars that require different intestinal transporter systems
(ie, glucose and fructose)
• Avoids saturation of any one transporter
– May increase carbohydrate absorption relative to using just a single sugar
Carbohydrate Metabolism
Glucose
Fructose
Glucose
intermediate
Galactose
Glycogen
Glycolysis
CO2
Pyruvate oxidation
Krebs cycle
(aka tricarboxylic acid
or TCA cycle)
Electron
transport
chain
Berg JM, et al. Biochemistry .5th ed. New York, NY: WH Freeman and Co.; 2002.
ATP
energy
Storage of Carbohydrate in the Body
 If glucose is absorbed, but not needed right away, the body stores
a small amount as glycogen
– Glycogen is a fluctuating storage pool for glucose
– The structure of glycogen is similar to starch
– Found in the liver and skeletal muscles
• Glycogen in liver is a reserve glucose supply to the brain
• Glycogen in muscles is an energy source for exercise
Berg JM, et al. Biochemistry .5th ed. New York, NY: WH Freeman and Co.; 2002.
Glycogen During Exercise
 During exercise, glycogen is broken down and glucose molecules
enter glycolysis (ie, energy metabolism)
 Vitamin B6 is a structural part of the enzyme that breaks down
glycogen
– Shows one of the many roles of B-vitamins in energy metabolism
 Glycogen can supply the body with only a limited amount of
energy
– Exogenous carbohydrates are important for high-intensity and long-duration
exercise
 Eat carbohydrates immediately after exercise for most rapid
glycogen replenishment (recovery)
– Ingestion of 50 grams of carbohydrate every 2 hours can result in up to 5%
glycogen replacement per hour
• Therefore, total replacement would take 20 hours
Hui YH. Handbook of Food Science, Technology, and Engineering. Volume 1. Boca Raton, FL: CRC Press; 2006:10-12.
United States Anti-doping Agency. Optimal dietary intake guide. Available at: http://www.usada.org/diet/?gclid=COOM-Ky95aYCFQTNKgodzVQL2w. Accessed
January 31, 2011.
Tardie G. The Sports Journal. Available at: http://www.thesportjournal.org/article/glycogen-replenishment-after-exhaustive-exercise. Accessed February 17, 2011.
II. Properties of Carbohydrates:
Considerations for Sports
Performance
Glycemic Response to Carbohydrates in Sports Nutrition
 Ingestion of carbohydrates affects both blood glucose levels
and insulin response (glycemic response)1
– Can influence energy sources during exercise
 One measure of glycemic response is the glycemic index (GI)2,3
 Glycemic load is a relatively new measure for glycemic
response4
– Based on the concept that exercise performance may be determined by
both carbohydrate ingestion and the glycemic response of the overall
diet
1. Mondazzi L and Arcelli E. J Am Coll Nutr. 2009;28:455S-463S.
2. Burke LM, et al. Int J Sport Nutr. 1998;8:401-415.
3. Donaldson CM, et al. Int J Sport Nutr Exerc Metab. 2010;20:154-165.
4. O’Reilly J, et al. Sports Med. 2010;40:27-39.
12
What Is the Glycemic Index?
 System of ranking foods according to how much they raise blood
glucose relative to a reference food
– Developed by Jenkins DJ, et al. Am J Clin Nutr. 1981;34(3):362-366.
 Rapidly digested or absorbed carbohydrates = high GI
 Slowly digested or absorbed carbohydrates = low GI
 References on GI
– Brand-Miller J, et al. The New Glucose
Revolution. 3rd ed. New York, NY:
Marlowe & Co.; 2006
• Written by experts on GI
– Atkinson, et al. Diabetes Care.
2008;31(12):2281-2283
• Most comprehensive table of the
glycemic index of foods that has
been assembled to date
Abbreviations: GI, glycemic index.
Figure from http://www.glycemicindex.com/aboutGI.htm.
What Does the Glycemic Index Value Mean?
 The glycemic index (GI) is expressed as a ratio comparing the
blood glucose increase caused by a test food to that of a reference
food (usually glucose, historically white bread) for 2 hours
following ingestion:
Area Under the Curve for Test Food
Area Under the Curve for Reference Food
 GI values:
Split peas = 25 ± 6
Golden delicious apples = 39 ± 3
Oatmeal = 51 ± 8
Raisin bran flake type of cereal = 61 ± 5
White bread = 75 ± 2
Long-grain white rice = 76 ± 7
Corn flake type of cereal = 81 ± 3
Atkinson FS, et al. Diabetes Care. 2008;31(12):2281-2283.
× 100
= GI
Slow and Fully Digested CHOs (Low GI)
 Isomaltulose1
– Glucose and fructose
– More steady and sustained release of glucose into the blood compared with
sucrose
– Occurs naturally in honey, but can be synthesized from sucrose
 Sucromalt2
+
– Produced by enzymatic conversion of sucrose and maltose into a fructose
and oligosaccharide syrup
• ~40% fructose, ~50% oligosaccharides, and ~10% other mono- and
disaccharides
– Digestion profile similar to isomaltulose
 Gamma-cyclodextrin (γ-CD)3
– Ring of 8 glucose molecules
Abbreviations: CHO, carbohydrate; GI, glycemic index.
1. Lina BA, et al. Food Chem Toxicol. 2002;40(10):1375-1381.
2. Xtend™ Sucromalt. Cargill, Inc. Available at: http://www.cargill.com/food/na/en/products/sweeteners/specialty-sweeteners/xtendsucromalt/index.jsp. Accessed February 24, 2011.
3. Munro IC, et al. Regul Toxicol Pharmacol. 2004;39:S3-13.
What Is the Glycemic Load?
 Takes into account the amount of carbohydrate in a common
serving in addition to its glycemic index
GL = (GI of CHO × gram CHO per serving) ÷ 100
 Example
– Carrots (peeled, boiled) have a GI of 47 and 5 g CHO per serving
The GL of carrots is: (47 × 5) ÷ 100 = 2.4
Abbreviations: CHO, carbohydrate; GL, glycemic load; GI, glycemic index.
Atkinson FS, et al. Diabetes Care. 2008;31(12):2281-2283.
Glycemic Index and Load Standards for Foods
 GI (based on glucose reference)
– Low GI
– Intermediate GI
– High GI
0-55
56-69
≥ 70
 GL
– Low GL
– Intermediate GL
– High GL
0-10
11-19
≥ 20
Abbreviations: GI, glycemic index; GL, glycemic load.
Brand-Miller J, et al. The New Glucose Revolution: The Authoritative Guide to the Glycemic Index-The Dietary Solution for Lifelong Health. 3rd ed. New York, NY:
Marlowe and Co.; 2006.
Brand-Miller JC, et al. Am J Clin Nutr. 2003;77(4):993-995.
Limitations of glycemic index approach before and during
exercise
 Clinical data have been mixed regarding the effectiveness of the glycemic index
(GI) in food choice before exercise
– Some discrepancies associated with how researchers evaluate exercise
performance
• Benefits observed in some time to exhaustion studies
• Mainly no benefits in studies of time trial performance
– No adverse effects of low glycemic index foods on performance have been
observed
 Carbohydrate ingestion during exercise can help maintain blood glucose and
eliminate the need for low glycemic index pre-exercise food
– Low glycemic index pre-exercise foods, though, may help reduce insulin
response (may positively affect fat utilization during exercise)
– If an athlete has inadequate access to carbohydrate during an event, low
glycemic index carbohydrates before event may be helpful
 Some of the low glycemic index foods used in research studies (e.g., lentils)
might not be palatable as pre-exercise foods for athletes
Burke LM, et al. Int J Sport Nutr. 1998;8:401-415.
Donaldson CM, et al. Int J Sport Nutr Exerc Metab. 2010;20:154-165.
18
What Is High-Fructose Corn Syrup?
 Cornstarch is converted to corn syrup that is essentially
100% glucose
 Enzymes and processing techniques convert some of the glucose
to fructose to achieve corn syrup that is 55% fructose (HFCS-55)
 HFCS-55 is the type of corn syrup used mainly in the beverage
industry
– Syrup is 55% fructose, 45% glucose
– Similar to 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; 2004:212-214.
The Truth About High-Fructose Corn Syrup
 Too much sugar, of any kind, in beverages is not recommended
– It is easy to consume too much energy, leading to weight gain
– Most sugar-sweetened beverages provide little to no vitamins, minerals, or
other essential nutrients
 However, there are no differences in metabolic responses to
high-fructose corn syrup vs sucrose in humans
– No differences in circulating hormones
– No differences in appetite or satiety-related variables (fullness)
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.
III. Training
Carbohydrates and Sports Nutrition
 Important for maximizing muscle glycogen stores
– Depleted muscle glycogen—“Hitting the wall”
– Depleted liver glycogen—“Bonking”
– Both phenomena are experienced as a precipitous loss of energy as a result
of low blood sugar
 Training and high carbohydrate diets maximize glycogen stores
United States Anti-doping Agency. Optimal dietary intake guide. Available at: http://www.usada.org/diet/?gclid=COOMKy95aYCFQTNKgodzVQL2w. Accessed January 31, 2011.
Ensminger A. Foods and Nutrition Encyclopedia 2nd Edition Volume 1. Boca Raton, FL: CRC Press LLC; 1994. Pages 1202-1203.
Burke L. Practical Sports Nutrition. Champaign, IL: Human Kinetics; 2007. Page 124.
Clark N. Sports Nutrition Guidebook 4th Edition. Champaign, IL: Human Kinetics; 2008. Page 119.
Carbohydrate and Fat Use at Different
Exercise Intensities
 As the intensity of exercise increases, muscle glycogen constitutes
a greater portion of the energy source
(Weightlifting,
sprinting, etc)
Energy Expended, cal/kg/min
300
(Soccer,
dancing, etc)
Muscle glycogen
200
Muscle triglyceride
100
0
(Leisurely walking,
slow cycling)
25
65
85
Maximal Oxygen Consumption, %
Abbreviations FFA, free fatty acid.
Romijn JA, et al. Am J Physiol. 1993;265(Part 1):E380-E391.
Plasma FFA
Plasma glucose
Carbohydrates in the Days Before Exercise
 High glycogen stores are very important to prolong endurance
– Related to diet and exercise in the days and hours before
exercising/competing
– Endogenous carbohydrate oxidation occurs at high intensity
– Especially important for events longer than 90-120 minutes
(eg, marathons and cycling events)
United States Anti-doping Agency. Optimal dietary intake guide. Available at:
http://www.usada.org/diet/?gclid=COOM-Ky95aYCFQTNKgodzVQL2w. Accessed January 31, 2011.
Latta S. Marathon & Beyond. 2003;7(5).
Carbohydrates 1 to 2 Hours Before Exercise
 Low glycemic index foods and beverages
– Especially important for endurance exercise
 Carbohydrates that are also low in fiber may be beneficial due to
varied gastrointestinal sensitivity among individuals
– Examples
• Fruit juices
• Bagels
• Breakfast cereals with < 3 g fiber/serving
• Potatoes
 Carbohydrate amounts vary among individuals, sport type, and
sport intensity
United States Anti-doping Agency. Optimal dietary intake guide. Available at:
http://www.usada.org/diet/?gclid=COOM-Ky95aYCFQTNKgodzVQL2w. Accessed January 31, 2011.
Wu CL and Williams C. Int J Sport Nutr Exerc Metab. 2006;16(5):510-527.
Carbohydrates During Exercise Are Also Important
 Jeukendrup (2004) reviewed multiple studies (n = 22) of walking,
running, and cycling in which carbohydrates were given
during exercise
– 23 of 36 observations within these studies showed a positive effect of
carbohydrate on endurance
– Effective dose
• Minimum, 16 to 22 g carbohydrate/hour
• Maximum, 75 g carbohydrate/hour
– No studies showed an adverse, or ergolytic, effect of carbohydrate
on performance
– Form of carbohydrate (solid or liquid) was of little significance, although
the vast majority of the studies used a beverage
 Sports beverages that include different types of sugars will be
absorbed via different sugar transporters in the gut
– Increase exogenous carbohydrate oxidation during exercise from 1.0 g/min
to 1.2 to 1.5 g/min
Jeukendrup AE. Nutrition. 2004;20(7-8):669-677.
Carbohydrates After Exercise
 Carbohydrates that are quickly digested and absorbed are
recommended postexercise to restore muscle glycogen levels
as fast as possible
– Glucose
– Maltose
– Maltodextrin
 Protein + carbohydrates postexercise maximizes the rate of
glycogen synthesis
 When intervals between exercise sessions are < 8 hours, consume
carbohydrates as soon as practical postexercise for fastest
recovery
Ivy JL, et al. J Appl Physiol. 2002;93:1337-1344.
Recommendations for Carbohydrate Intake
During Recovery
 Carbohydrate intakes are expressed per kga not % of energy
– For immediate recovery after exercise (0 to 4 hours)
• 1.2 g/kg/hr consumed at frequent intervals
 For daily recovery, range of 3-12 g/kg/day; adjust with
consideration of:
–
–
–
–
aMultiply
Athlete’s total energy needs
Specific training needs and stage of training
Feedback from training performance
Training intensity
• 3-5 g/kg/day: very light training programs (low-intensity or skill-based
exercise)
• 5-7 g/kg/day: moderate intensity training programs for 60 min/day
• 6-10 g/kg/day: moderate- to high-intensity endurance exercise for 1-3
hours per day
• 8-12 g/kg/day: moderate- to high-intensity exercise for 4-5 hours/day
the numbers by 0.45 to get carbohydrate intake in grams per pound of body weight.
Burke LM, et al. J Sport Sci. 2004;22(1):15-30.
Putting Together a Meal Plan
 Example:
– 70-kg athlete requiring 4000 kcal/day and exercising 120 min/day 4 to 6
times/week
 Macronutrient Target Recommendations
– Grams/kg (body weight)/day
• Carbohydrate
• Protein
• Fat
7 to 10 g/kg/day (490 to 700 g/day)
1.5 to 2.0 g/kg/day (105 to 140 g/day)
Typically use percentage of energy as method
– Percentage of energy
• Fat
20% to 35% of energy (88 to 156 g/day)
– Target recommendations for this athlete
• Carbohydrate
• Protein
• Fat
600 g (60% of energy)
130 g (13% of energy)
120 g (27% of energy)
A Potential Distribution of Macronutrients Over the
Course of 6 Meals/Day
Meal
Time
Carbohydrate, g
Protein, g
Fat, g
Breakfast
7:00 AM
90
15
15
Mid-AM snack
10:00 AM
25
10
5
Noon
75
20
20
Pre-Ex meal
1:30 - 2:00 PM
90
10
5
During Ex
3:00 - 5:00 PM
100
0
0
Post-Ex meal
5:00 PM
75
30
25
Dinner
6:30 PM
120
30
35
PM snack
9:00 PM
25
15
15
600
130
120
Lunch
TOTALS
Foods Containing Approximately
25 to 30 g Carbohydrate
 1 cup of juice or 1 large piece of fruit
 1 bagel or 2 slices of bread
 1 cup of most cereals
 1 large baked potato
 2 cups of milk
 ⅔ cup of dried beans
 1 cup of rice or corn
 1 cup of squash (other non-starchy vegetables have less
carbohydrate)
 2 cups of commercial sports/electrolyte replacement drink
 ½ to 1 energy bar (1 bar  25 to 45 g carbohydrate)
 1 pack of energy gel ( 25 g carbohydrate)
Atkinson FS, et al. Diabetes Care. 2009;31(12):2281-2283.
Examples of Postexercise Meals
 Option 1
–
–
–
–

1 regular bagel
2 Tablespoons peanut butter
8 fl oz skim milk
1 medium banana
Meal provides 562 kcal, 77 g carbohydrate, 23 g protein, and 18 g fat
 Option 2
– 17-oz commercial nutrition shake
 Provides 300 to 420 kcal, 17 to 70 g carbohydrate, 32 to 42 g protein,
and 2 to 16 g fat
IV. Competitions
Competition
 Competitions sometime require different carbohydrate intakes
than practice
– Endurance may be required for a longer amount of time
– Maximum glycogen levels are optimal for best performance and require
time to build (on the order of days; not possible for practices)
 Do not try any new foods in competition before you try it at least
once at practice
Carbohydrates as Energy at Different Times
 Carbohydrate consumed in the days before event
– Used to provide adequate glycogen stores in muscle
• Prevent “hitting the wall”
 Carbohydrate consumed in the hours before the event
– Used to preserve liver glycogen stores, which can deplete after
approximately 8 to 12 hours of fasting
 Carbohydrate consumed during event
– Used to maintain blood glucose, especially when liver glycogen is depleted
• Carbohydrate in the hours before and during exercise helps to prevent
“bonking”
United States Anti-doping Agency. Optimal dietary intake guide. Available at: http://www.usada.org/diet/?gclid=COOMKy95aYCFQTNKgodzVQL2w. Accessed January 31, 2011.
Ensminger A. Foods and Nutrition Encyclopedia 2nd Edition Volume 1. Boca Raton, FL: CRC Press LLC; 1994. Pages 1202-1203.
Burke L. Practical Sports Nutrition. Champaign, IL: Human Kinetics; 2007. Page 124.
Clark N. Sports Nutrition Guidebook 4th Edition. Champaign, IL: Human Kinetics; 2008. Page 119.
Carbohydrate Loading
 Traditional protocol
– Depletion of glycogen stores (~ days 6 to 3 before event)
• Low-carbohydrate diet and hard exercise
– Supercompensation of muscle glycogen (during the 36 to 48 h prior to
event)
• Very high-carbohydrate diet (10 to 12 g/kg body weight/day)
and tapering of exercise
 Cons
– Depletion phase is hard on the body and difficult to tolerate
in training
• May lead to headaches, irritability, and increased risk
of injury
Pre-Competition Meal
 One of the most variable aspects of the athlete’s diet
– Depends on individual tolerance
– Athletes often have certain beliefs about food’s effect
on performance
– Ranges from no food to the old “steak and eggs” breakfast
– Depends on the sport to some degree
 Functions of the pre-event meal
–
–
–
–
Prevent dehydration
Maintain adequate muscle and liver glycogen levels
Avoid excess hunger feelings
Confidence in preparation for the event
Pre-Competition Meal (continued)
 Medium amount of energy
– 300 to 500 kilocalories, more if there is time to digest before the event
 2 to 3 hours before event (perhaps 1 hour with liquid meal)
– Ingestion of carbohydrate 1 hour before exercise does not usually
impair performance
– Depends on individual tolerance
 Liquid meals are popular for gastrointestinal comfort during
the event
 GI of pre-event carbohydrates
– No solid evidence for this, experiment in practice
 Include 1 to 2 cups of fluid
 Avoid foods with a high fat content and/or excess fiber
Abbreviations: GI, glycemic index.
Examples of Pre-Competition Meals
 Option 1, liquid meal (blend all ingredients)1
–
–
–
–

1 cup of vanilla yogurt
4 to 6 peach halves, canned or fresh
4 graham cracker squares
Dash nutmeg, optional
Meal provides 450 kcal, 75% CHO, 15% protein, and 10% fat
 Option 2
Food
Kcal
Carbohydrate, g
Protein, g
Fat, g
Oatmeal, instant 1 pkt
104
18
4
2
Skim milk, ½ cup
43
6
4
0
Toast, 2 slices
146
24
4
2
Banana, 1 medium
105
27
0
1
Orange juice, 6 oz
84
20
1
0
TOTAL
482
95 (80%)
13 (11%)
5 (9%)
Abbreviations: CHO, carbohydrate; pkt, packet.
1. Clark N. Sports Nutrition Guidebook. Champaign, IL: Human Kinetics; 1989.
Carbohydrates During Competition
 Consuming carbohydrate is neither practical nor necessary during
exercise lasting less than 45 minutes
 Small amounts of carbohydrate from sports drinks or foods may
enhance performance during sustained high-intensity exercise
lasting 45-75 minutes
 Athletes should consume 30-60 g carbohydrate per hour from
carbohydrate-rich fluids or foods during endurance and
intermittent, high-intensity exercise lasting 1-2.5 hours
 During endurance and ultra-endurance exercise lasting 2.5-3 hours
and beyond, athetes should consume upt to 80-90 g carbohydrate
per hour
– Products providing multiple transportable carbohydrates are necessary to achieve
these high rates of carbohydrate oxidation
Jeukendrup AE. Nutrition. 2004;20(7-8):669-677.
Burke LM, et al. Carbohydrates for training and competition. J Sport Sci. 2011 (in press as of April 2011).
Summary of Key Messages
 A diet with high carbohydrate availability helps to maximize
glycogen stores and generally increases exercise performance
 Consuming carbohydrate during exercise also generally helps
performance
– Experiment in practice regarding tolerated levels
– Liquid carbohydrates also help with hydration
 Eating as soon as possible after exercise promotes the most
rapid recovery of muscle glycogen
– Combination of carbohydrate and protein may facilitate this process
 Frequent, smaller meals can help athletes with high energy and
carbohydrate requirements get in the required amounts of
nutrients