Carbohydrates in exercise

1. NUTRITION FOR SPORT
AND EXERCISE
NDD30503
ASSOC PROF. DR. SHARIFAH WAJIHAH WAFA BTE SST
WAFA
EC22
SUNDAY
1000-1200

2. Carbohydrates
Lecture 3

3. 1. Classify carbohydrates according to their
chemical composition.
2. Describe the digestion and absorption of
carbohydrates.
3. Explain the metabolism of glucose.
4. Describe how muscle glycogen and blood
glucose are used to fuel exercise.
Learning Objectives

4. 5. Detail and explain carbohydrate
recommendations for athletes, including
specific guidelines for intake before, during,
and after exercise.
6. Determine the daily carbohydrate needs of an
athlete, and select carbohydrate-containing
foods to meet the recommended intake.
Learning Objectives

5. 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

6. 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.

7. 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.

8. RECALL

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

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

11. Digestion, absorption, and transportation
of carbohydrates

12. 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

13. Metabolism of glucose in the body

14. 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

15. Metabolism of glucose in the body
 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
i. Low GI
• Blood glucose and insulin concentrations rise slowly
• Legumes, beans, and nonstarchy vegetables

16. Metabolism of glucose in the body

17. Metabolism of glucose in the body
 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

18. Metabolism of glucose in the body
 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

19. Metabolism of glucose in the body
 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

20. Metabolism of glucose in the body
 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)

21. Carbohydrates as a source of energy for
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
• may occur after 60 or
more minutes of
exercise at a hard
aerobic intensity.

22. Carbohydrates as a source of energy for
exercise
 Exercising muscle takes up and metabolizes blood
glucose.
• Exercise has an insulin-like effect
• 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

23. Carbohydrates as a source of energy for
exercise
 Exercise training increases the capacity for
carbohydrate metabolism.
• Aerobic training increases aerobic capacity of
muscle
a. Increased number and size of mitochondria
b. Increased oxidative enzyme activity
c. Increased muscle glycogen stores
d. Enhanced oxidative capacity increases fat
utilization as well

24. Carbohydrates as a source of energy for
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. May be difficult to train with low CHO stores
d. May compromise immunity

25. Carbohydrates as a source of energy for
exercise
 Glucose metabolism during exercise is
controlled by hormones.
• Glucagon
• Stimulates break down of liver glycogen
• Stimulates gluconeogenesis
• Epinephrine and norepinephrine
• Stimulate glycogen breakdown
• Stimulate gluconeogenesis
• Cortisol
• Stimulates amino acid breakdown and
gluconeogenesis

26. Carbohydrates as a source of energy for
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

27. 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
• Fine-tuning of general recommendation needed
to match training demands
 The amount of CHO in an athlete’s diet should
be based upon body weight and NOT a
percentage of the overall diet to ensure
adequate intake.

28. Carbohydrate recommendations for
athletes
• Replenishment of depleted glycogen stores
i. 5 g/kg/day is the minimum needed to replenish
ii. 5-7 g/kg/day recommended for power (strength)
athletes
iii. 5-7 g/kg/day does NOT completely restore to pre-
exercise levels for endurance athletes in heavy
training
iv. Endurance athletes in heavy training may need 8-
10 g/kg/day
v. Intermittent, high-intensity athletes in heavy training
have similar needs to endurance athletes
vi. Ultraendurance athletes may need more than 10
g/kg/day at times

29. Carbohydrate recommendations for
athletes
 Athletes need to plan their CHO intake before, during,
and after training and competition.
1. Intake prior to training and competition
a. Beneficial for endurance athletes and those in “stop and
go” sports
b. Amount and timing are related
 “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

30. Carbohydrate recommendations for
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. General recommendations
30-60 g CHO per hour
CHO concentration of 6-8% (60-80 g in 1,000
ml)
Spotlight on... Sports Drinks, Bars, and Gels –
Available forms of CHO

31. Carbohydrate recommendations for
athletes
d. Presence of other nutrients before & during
competition/effects on performance
e. Trial and error is important

32. Carbohydrate recommendations for
athletes
3. Intake after training and competition
a. Ideal physiological environment for restoring
muscle glycogen
b. General recommendations
 CHO consumption as soon as practical after exercise
 Meal size: Small, frequent CHO-containing meals
 Type of CHO: CHO foods with a high glycemic index
 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

33. Carbohydrate recommendations for
athletes
 Muscle glycogen stores can be maximised by diet and
exercise manipulation.
1. CHO loading – Also known as CHO super compensation
2. Used by endurance athletes and some body builders
3. Goal is to obtain maximum muscle glycogen storage
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

34. Carbohydrate recommendations for
athletes
 Training and performance may be impaired if insufficient
CHO is consumed.
1. Adequate daily energy intake is important
2. Most athletes do not meet CHO recommendations
3. Insufficient CHO intake leads to low muscle glycogen
levels
4. Acute and chronic fatigue may result from low CHO
intake
5. Adequate CHO may reduce risk for immune system
suppression in endurance athletes

35. 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.

36. Translating daily carbohydrate
recommendations to food choices
 A carbohydrate-rich diet requires planning.
1. Meeting CHO needs daily takes some planning
2. Calculations may be made based on kg of body
weight
3. Number of serving per food group may be
helpful
• Fruits
• Vegetables
• Grains
• Beans
• Milk
• Sugar

37. Translating daily carbohydrate
recommendations to food choices
 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

38. Translating daily carbohydrate
recommendations to food choices
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

39. RECAP
Carbohydrate Metabolism During Exercise
Carbohydrate Reserves and Dietary Intake
Carbohydrate Feeding Before, During and After
Exercise
Determine the daily carbohydrate needs