Carb needs for athletes

NUTRITION FOR SPORT
AND EXERCISE
NDD30503
ASSOC PROF. DR. SHARIFAH WAJIHAH WAFA BTE SST WAFA
sharifahwajihah@unisza.edu.my

1. Describe how muscle glycogen and blood
glucose are used to fuel exercise.
2. Detail and explain carbohydrate
recommendations for athletes, including
specific guidelines for intake before, during,
and after exercise.
3. Determine the daily carbohydrate needs of
an athlete, and select carbohydrate-containing
foods to meet the recommended intake
Learning Objectives

Introduction
 Primary energy source for moderate to intense
exercise
 Carbohydrates (CHO) are found in food as
sugars, starches, and cellulose
 CHO are found in the body as glucose and
glycogen
 CHO stores are depleted by training and must
be replenished
 Proper amount and timing of CHO before,
during, and/or after exercise

Carbohydrates in food
 CHO are found as
• single sugars (monosaccharides)
• two linked sugar molecules (disaccharides), or
• many sugar molecules linked together
(polysaccharides).
 CHO vary in their sweetness and in the blood
glucose and insulin response to their
consumption.

Carbohydrates in food
 CHO are often classified as simple sugars and
starches, or complex carbohydrates.
 CHO of different types should not be considered
good or bad, but appropriate or inappropriate
considering the athletes’ goals and general
health.

 Carbohydrates are found in various forms in
food.
1. Monosaccharaides
a. ____________
b. ____________
c. ____________
2. Disaccharides
a. ____________
b. ____________
c. ____________

 Carbohydrates are found in various forms in
food.
3. Polysaccharides
a. ___________
b. ___________
c. ___________
 Sugar Alcohol
a. ___________
b. ___________
c. ___________
d. ___________

Digestion, absorption, and
transportation of carbohydrates

Digestion, absorption, and transportation
of carbohydrates
 Glucose and fructose are absorbed by different
mechanisms.
i. Glucose and galactose are absorbed into the intestinal
epithelial cells by active transport by a sodium and glucose
transporter (SGLT) and into the blood by facilitated diffusion
through the GLUT-2 glucose transporter; Portal vein to liver,
circulates in blood
i. Fructose is absorbed into the intestinal epithelial cell by
facilitated diffusion by the GLUT-5 transporter and into the
blood by the same process and transporter (GLUT-2) as
glucose; Trapped in liver and converted to glucose

Metabolism of glucose in the body

 The body normally maintains blood glucose within a
fairly narrow range, approximately 4.0 to 5.4 mmol/L
 Insulin secreted in response to hyperglycemia
 Glucose circulating in the blood is taken up into various
tissues through GLUT found in their cell membranes.
a. Brain, liver, and exercising muscle cells can take up
glucose without insulin
b. GLUT-4 – most abundant, responds to insulin
c. GLUT-4 participates in insulin-dependent glucose
transport

 Glucagon secreted in response to hypoglycaemia
• Hypoglycaemia: < 3.5 mmol/l
 Insulin and glucagon are counter-regulatory
 Glycaemic effect of various carbohydrates and the
glycaemic index
a. Glycaemic response
i. Effect on blood glucose and insulin concentrations
b. Spotlight on... Glycaemic Index (GI)
i. Classification of CHO foods based on glycaemic response
ii. High GI
• Blood glucose and insulin concentrations rise quickly
• Highly refined starchy foods and starchy vegetables
iii. Low GI
• Blood glucose and insulin concentrations rise slowly
• Legumes, beans, and nonstarchy vegetables

 Glucose can be metabolized immediately for
energy.
a. Process depends on energy need of cell and
enzymatic capability
b. Red blood cells must use glucose (no
mitochondria)
c. Fast-twitch muscle fibres prefer to use CHO via
anaerobic glycolysis
d. Slow-twitch muscle fibres prefer to use CHO via
aerobic metabolism

 Glucose can be stored as glycogen for
later use.
a. If energy need of cell is low, stored as
glycogen
b. Insulin (fed state) favours glycogen storage
c. Glycogen depletion favours glycogen
storage
d. Glycogen synthase is the primary enzyme

 Products of glucose metabolism can be used to
synthesise fatty acids.
a. Not likely to occur if training because
glycogen storage is favoured
b. More likely to occur in sedentary people who
over-consume kcal and CHO
c. Glucose is indirectly stored as fat
• Glucose converted to acetyl CoA and incorporated
into fatty acids (lipogenesis)
• Fatty acids stored in adipose tissue

 Glucose can be produced from lactate, amino
acids, and glycerol by a process called
gluconeogenesis.
• Limited ability to produce glucose from non-CHO
sources
• Lactate to glucose (Cori cycle in liver)
• Amino acids to glucose (e.g., alanine in liver)
• Glycerol to glucose (limited ability in liver)

CARBOHYDRATES AS A SOURCE OF
ENERGY FOR EXERCISE

Carbohydrates as a source of energy for
exercise
 Muscle can use variety of fuel sources to provide
energy
• Creatine phosphate
• Carbohydrates
• Fats
• Proteins
 The fuel source utilised depends on exercise
intensity-
• i.e very high intensity, very short duration
anaerobic exercise uses creatine phophate

exercise
 CHO used by exercising muscle can come from
• Stored muscle glycogen OR
• Glu that is brought into the muscle from the blood
 Glu is made available in the blood from the liver
as a result of at least THREE processes
1. The breakdown of liver glycogen
2. The production of glucose from other sources
(gluconeogenesis)
3. Ingestion of CHO as food or fluids, which are
absorbed and passed through the liver

exercise
 Exercising muscle first uses
carbohydrate stored as
glycogen.
• Exercising muscle prefers to use
glycogen even when blood
glucose is available
• Muscle glycogen depletion is
associated with fatigue
• During prolonged exercise
• Occur in intermittent high-
intensity exercise i.e repeated
sprints that occur during
soccer matches

exercise
 Exercising muscle takes up and metabolizes blood
glucose.
• Exercise has an insulin-like effect (uptake glu from
the blood)
• Homeostasis is maintained initially by:
• Glycogenolysis in liver- stimulates the breakdown of liver
glycogen to release more glucose into the blood
• Gluconeogenesis in liver- stimulates the production of more
glucose by the liver
• Pathways are limited so blood glucose concentration
can decline with prolonged exercise
• Exercising muscle prefers to use glycogen over
blood glucose

exercise
 Exercise training increases the capacity for
carbohydrate metabolism.
• Aerobic training increases oxidative (aerobic)
capacity of muscle
a. Increased number and size of mitochondria
b. Increased oxidative enzyme activity
c. Increased muscle glycogen stores
d. Increased the ability of the muscle to metabolise
fat for energy

exercise
 “Depletion workouts” or “training low” strategy –
intended to enhance fat metabolism
a. Training with low carbohydrate stores (via
dietary CHO restriction)
b. May increase mitochondrial function
c. However, may be difficult to train with low CHO
stores
d. May compromise immunity- exposing the
athlete to increased risk of illness or injury.

exercise
 Glucose metabolism during exercise is
controlled by hormones.
• Glucagon- secreted during periods of fasting or
starvation and exercise
• Stimulates break down of liver glycogen
• Stimulates gluconeogenesis
• Epinephrine and norepinephrine
• Stimulate glycogen breakdown
• Stimulate gluconeogenesis
• Cortisol
• Stimulates amino acid breakdown and
gluconeogenesis

exercise
 Exercise intensity affects carbohydrate
metabolism.
• As exercise intensity increases, % energy from
CHO increases
• CHO is main source of energy for moderate- to
high-intensity exercise

KEY POINTS
1. Exercising muscle prefers to use muscle glycogen
2. Muscle glycogen may be depleted and fatigue may
occur after 60 or more minutes of exercise at a hard
aerobic intensity
3. Exercise has a strong insulin-like effect, stimulating
the uptake of glucose from the blood.
4. Exercise stimulates the breakdown of liver glycogen
to release more glucose into the blood and stimulates
the production of > glucose by the liver by
gluconeogenesis

KEY POINTS
5. The breakdown of liver glycogen, glycogenolysis and
the increase in gluconeogenesis during exercise is
stimulated by the hormone glucagon
6. As exercise intensity increases, the proportion of
energy derived from CHO metabolism increases

CARBOHYDRATE
RECOMMENDATIONS FOR ATHLETES

Carbohydrate recommendations for
athletes
 Daily CHO intake is based upon individual
needs to meet the long-term demands of
training and competition.
• General CHO recommendation: 5-10 g/kg body
weight daily (ADA)
• Fine-tuning of general recommendation needed
to match training demands

athletes
Exercise intensity and
duration
Examples of sports Daily carbohydrate
Very high intensity, very
short duration (< 1 min)
5-7 g/kg
High intensity, short
duration (1 to 30 minutes
continuous)
Track (200 to 1500m)
Swimming (100 to
1500m)
Cycling (short distance)
Rowing (crew)
5-7 g/kg
High intensity, short
duration (1 to 30 minutes
with some rest periods)
Gymnastics
Wrestling
Boxing
Judo
Taekwondo
5-8 g/kg

athletes
duration
Moderate intensity,
moderate duration (30 to
60 min)
10 km running (elite
runners finish in <30
min)
6-8 g/kg
Intermittent high
intensity, moderate to
long duration (> 1 hr)
Football
Basketball
Field Hockey
Tennis
Water polo
6-8g/kg; 8-10 g/kg during
heavy training and
competition
Moderate intensity, long
duration (1 to 4 hrs)
Distance running
(marathon)
Distance swimming
Distance cycling
8-10 g/kg during heavy
training and competition

athletes
duration
Moderate intensity,
ultralong duration (>4
hrs)
Ultradistance running
Ultradistance swimming
Ultradistance cycling
Triathloton
Adventure sports
8-10 g/kg or depending
on the stage of training
Low intensity, long
duration (more than 1 hr)
Golf
Baseball
Softball
5-7g/kg
Other Bodybuilding 5-10g/kg depending on
the stage of training

athletes
 Expressing CHO recommendations
• The amount of CHO in an athlete’s diet should be
based upon body weight.
• NOT a percentage of the overall diet to ensure
adequate intake.
Ms Y Ms X
Total CHO intake 350 g 245 g
Total energy intake 2000 kcal 1400 kcal
% energy intake as
CHO
70% 70%
CHO (g) per kg of
BW
6.4 g/kg 4.5g/kg
*Usual recommendation for most athlete is 50-65%

athletes
1. Intake prior to training and competition
a. GOAL: Avoiding hunger, delaying fatigue,
minimising GI distress and preventing hypo
hydration.
b. Fine tuning both the amount and timing:
CHO intake up to 3 or 4 hours prior to endurance exercise
 “Rule of thumb” = 1 g/kg one hr prior to exercise, 2
g/kg 2 hr prior
 Glycemic index is NOT an issue for most athletes
 May be convenient to consume CHO in liquid form –
Considerations should be made for the form of CHO and
convenience
 Trial and error is important

athletes
 Gatorade
• Energy: 100 kcal
• CHO (g): 25
• Fiber (g): 0
• Protein (g): 0
• Fat (g): 0
• Recommended time: 15
minutes before exercise

athletes
2. Intake during exercise training and competition
a. Beneficial for endurance and ultra endurance
athletes
b. May be beneficial for those in “stop and go” sports
c. To spare muscle glycogen, maintain blood glucose
concentrations, delay fatigue and reduce the
athlete’s perception of fatigue
d. General recommendations
30-60 g CHO per hour
Beverages (sports drink) contain CHO concentration of 6-8%
(60-80 g in 1,000 ml)

athletes
e. Presence of other nutrients before & during
competition/effects on performance
f. Trial and error is important

CHO intake during exercise to enhance
performance
duration
Examples of sports Recommended CHO
intake to enhance
performance
High intensity <45mins Running (sprints up to 10km)
Cycling
Swimming (sprints up to
1500m)
Rowing (crew)
none
High intensity exercise
(continuous or intermittent)
approx. 45-60 mins
Team sports: basketball,
water polo, ice hockey
Cycling time trials
0-30g/h
High-intensity exercise
(intermittent) approx 90
mins
Team sports: Football Skilled
recreational tennis player
Team or individual handball
or squash
30-50g/h

CHO intake during exercise to enhance
performance
duration
Examples of sports Recommended CHO
intake to enhance
performance
Moderate to vigorous
exercise > 2 hrs
Backpacking, hiking
Recreational cycling
30-60g/h**
High-intensity exercise >
2hrs
Marathon running
Sprint
Olympic distance triathlon
50-70g/h**
Ultra endurance
competitions lasting many
hours or repeated days
Ironman length triathlons
Cycling stage races
Adventure racing
60-90g/h**
** The maximal rate of CHO absorption from the GI tract is estimated to be 60g/h. If
need approaches or exceeds this amount, it may be helpful to consume sports
beverages that contain a variety of sugars, such as glucose, fructose, sucrose,
galactose, maltodextrin, isomaltulose, amylose, amylopectin/and or trehalose.

athletes
 Developing a carbohydrate intake plan during
exercise must take into account a number of
practical issues
• Duration and intensity of the exercise
• Type of exercise and opportunity or ease of
food/fluid consumption
• Food/fluid preferences of the athlete
• Availability of CHO sources

APPLICATION EXERCISE
A 46-year-old male runner is planning to run the Adidas Marathon.
He is a well-trained runner, having had some success in 10-
kilometer and half-marathon distance races but has fatigued and
slowed down in the late stages of the two previous marathon he
has run.
Develop a specific plan for carbohydrate consumption for this
athlete to ensure that he consumes sufficient CHO during the
marathon. Assume he weighs 75kg and that Gatorade is available
at aid stations every 2-4 kilometer. Bananas also available at aid
stations between 40 and 48 km.
The plan should include instructions for timing, amount, and type
of CHO intake during the race, including practical suggestions.

athletes
3. Intake after training and competition
a. To optimise glycogen replacement, TWO things are needed:
CHO and insulin
b. Guideline for optimal muscle glycogen re-synthesise
 Timing: should be consumed as soon as the exercise
session or competition is over
 Meal size: Small, frequent CHO-containing meals
 Type of CHO: contain mostly glucose and/or sucrose; CHO
foods with a high glycemic index
 Amount of CHO: For maximum resynthesise: 1.5 g/kg
within the first hour and 0.75-1.5 g/kg each hour for the next
three hours
 Addition of protein or amino acids

athletes
 Muscle glycogen stores can be maximised by diet and
exercise manipulation.
1. CHO loading – Also known as CHO super compensation
2. to attain max glycogen stores prior to an important
competition
3. Used by endurance athletes and some body builders
4. “Classical” approach was to severely deplete and then
replete
5. “Modified” approach eliminates severe depletion stage
6. General recommendation: 10 g/kg/day 3 days prior to
event

athletes
Day 2Day 1 Day 3 Day 5Day 4 Day 6 Day 7
Cycle@75%toexhaustion
Fat + Protein diet High CHO: 8.2g/kg/d
“Classical” CHO-loading protocol

athletes
Day 2Day 1 Day 3 Day 5Day 4 Day 6 Day 7
90minrun@75%
20.9kmtimetrial
Mix diet High CHO diet
“Modified” CHO-loading protocol
40minrun
40minrun
20minrun
20minrun
rest

athletes
 Training and performance may be impaired if insufficient
CHO is consumed.
1. Adequate daily energy intake is important
• Insufficient total energy intake means that some of the CHO
consumed will be used for immediate energy and will be
unavailable for storage as muscle/lover glycogen
2. Insufficient CHO intake leads to low muscle glycogen
levels
3. Acute and chronic fatigue may result from low CHO
intake
4. Months of low CHO intake, in conjunction with a long-
term negative energy balance, are factors that contribute
to overtraining syndrome.

KEY POINTS
1. The recommended daily intake of CHO for athletes is 5 to
10g/kg/day, depending upon the intensity and duration of training
and competition, although ultra endurance athletes may need
during certain training periods.
2. CHO intake should be adjusted according to sport specific needs
as well as training and competition levels.
3. The amount of CHO in an athlete’s diet should be based upon
body weight and not % of the overall diet to ensure adequate
intake
4. In order to optimise the body’s stores, a CHO-containing meal
should be eaten 1-3 hours before training or competition. The
timing of the meal and the amount and type of CHO should be
individualised.

KEY POINTS
8. 30-60g of CHO should be consumed each hour during prolonged
or high-intensity intermittent exercise
9. If exercise has been prolonged and/or is intense enough to result
in substantial muscle glycogen depletion, CHO should be
consumed ASAP after exercise to stimulate the re-synthesis of
muscle glycogen
10. Pre-exercise muscle glycogen stores can be maximised by
manipulating exercise and CHO content of the diet in the days
before competitive event in a process called CHO loading
11. Endurance or high intensity training may be impaired if insufficient
CHO and the body’s CHO stores are lowered.

TRANSLATING DAILY CARBOHYDRATE
RECOMMENDATIONS TO FOOD
CHOICES

Translating daily carbohydrate
recommendations to food choices
 Athletes must plan carefully to ensure adequate
intake of CHO on a daily basis.
 Athletes must be knowledgeable about making
good food and CHO choices when dining out.
 Vegetarian diets typically contain a high
percentage of carbohydrate-rich foods but care
must be taken to consume an adequate total
amount of carbohydrates.

 75 kg cyclists
 CHO requirement: 8-10g/kg/day
 75 kg of BW x (8-10) g of CHO = 600 – 750g of
CHO
 1 g CHO = 4 kcal
 600- 750 g x 4 = 2400 – 3000 kcal from CHO
ALONE!

 A carbohydrate-rich diet requires planning.
1. Number of serving per food group may be
helpful
• Fruits
• Vegetables
• Grains
• Beans
• Milk
• Sugar

 Diet planning for carbohydrate intake must
consider practical issues.
1. Having CHO-rich food available
2. Choosing CHO-rich meals in fast-food and other
restaurants
3. Vegetarian diets: Many choices
• Some vegetarians consume animal products (e.g.,
dairy)
• Vegans exclude all foods of animal origin
• Well-planned vegetarian diets are healthful and
appropriate for athletes

4. Sugar intake and the use of artificial sweeteners
• High sugar intake may increase risk for some
chronic diseases (controversial)
• Exceptionally high intake of high-fructose corn
syrup is a concern
• Most adults use some artificial sweeteners
• Safety of artificial sweeteners has always been
controversial
• Artificial sweeteners have not been the panacea
once hoped for

5. Lactose Intolerance
6. Fructose Intolerance
7. Diabetes
• Will need to match their food intake with the
proper amount of insulin
• Reduce intake of high-glycaemic index foods

KEY POINTS
1. Athletes must plan carefully to ensure adequate
intake of CHO on a daily basis
2. Having CHO-rich foods available increase the
likelihood of making good food choices and
adhering to the dietary plan for CHO intake
3. Athletes must be knowledgeable about making
good food and CHO choices when dining out
4. CHO in the diet may be influnced nu individual
situations, such as lactose intolerance, fructose
intolerance or altered glucose and/or insulin
responses (i.e diabetes)

Carb needs for athletes

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