CARBOHYDRATES and EXERCISE

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CARBOHYDRATES and EXERCISE
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CARBOHYDRATES, HORMONES, AND ENDURANCE
PERFORMANCE

• Sports Science Exchange 80 VOLUME 14 - NUMBER 1

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EXERCISE
Endocrine Glands
Endocrine Glands
Blood
Blood

• Increase in blood levels of
• Growth Hormone (GH)
• Glucagon
• Cortisol
• Epinephrine Norepinephrine

Adipose cells
Liver cells
Glycogen Glucose
Triglycerides Fatty Acids
Skeletal muscle

Glycogen Glucose
Fatty Acids
GLUT-4
Blood
Increase in fatty acid Increase in glucose.
Fatty acids Glucose
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Hormones and Fuel Regulation

• Hormones help to maintain blood glucose levels
  and spare glycogen by mobilizing other fuel
  sources (e.g. fats).

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Insulin and Glucagon
Increase in Glucagon - breakdown of liver
glycogen which increases blood glucose
Decrase in insulin prevents glucose from
entering non-exercising cells
During Exercise
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Insulin and Glucagon
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GLUT-4 Protein

• Since insulin levels drop during exercise, how
  does glucose enter the muscle cells?
• GLUT-4 proteins assists in transporting glucose
  inside cells
• At rest they work with insulin in all cells
• During exercise, when insulin levels drop, GLUT-4
  is further activated by muscle contraction
• Therefore, glucose primarily enters only those
  cells (muscle cells) that need it the most

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Glucose Uptake (Getting It Inside the Cells)

• Insulin
• All cells
• Most active at rest
• Decreases during exercise

• GLUT-4
• Muscle cells
• Most active during exercise
• Increased during exercise due to contracting
  muscles

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Catecholamines
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Cortisol
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Growth Hormone
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Hormonal Regulation of Glucose During Exercise

• Glucagon, Epinephrine, Norepinephrine and
  Cortisol
• Breakdown glycogen (liver) to glucose
• Glucose levels in the blood remain fairly constant

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Hormonal Regulation of Fats

• Epinephrine, Norepinephrine, Growth Hormone,
  (Coritsol next slide)
• Breakdown of triglycerides in adipose tissue into
  fatty acids
• Fatty acids are transported to through the
  cardiovascular system to the muscles

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Glucoregulatory Hormones
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Hormones and Fuel Regulation

• Stress hormones may increase fatigue by depleting
  carbohydrate reserves faster than needed

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Carbohydrates During Exercise

• Ingesting sports drinks can delay fatigue.
• Less EPI, cortisol, glucagon, and GH
• 30-60 grams per hour to prevent hypoglycemia

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How Does Glucose Ingestion Help?

• Increase energy
• Glycogen sparing effect
• Enhance brain function
• reduced sense of effort
• improved motivation
• better mood
• reduced inhibition of central motor drive

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How Does Glucose Ingestion Help?

• Carbohydrate intake will help to maintain glucose
  levels
• Reduction in hormone levels
• Spare glycogen
• Lower free fatty acids
• Less free tryptophan in the blood
• Less tryptophan is converted into serotonin
  inside the brain
• Lowers ammonia levels

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Key Points

• Prolonged strenuous exercise increases plasma
  concentrations of the hormones epinephrine,
  growth hormone, cortisol, and glucagon. Insulin
  is decreased.
• Ingestion of carbohydrate during prolonged
  exercise blunts these hormone responses and
  delays fatigue.
• The blunted hormone response may contribute to a
  delay in both central (brain) and peripheral
  (muscle) fatigue by helping to spare liver and
  muscle glycogen, maintain blood glucose, and
  reduce blood concentrations of free fatty acids,
  free tryptophan, and ammonia.
• To prevent a fall in blood glucose concentration
  and to blunt the hormonal response to exercise,
  every 15-20 min athletes should drink 8-12 oz
  (240-350 ml) of a sports drink that contains
  carbohydrate.

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Summary

• Late stages of prolonged exercise are often
  associated with large increases in
  glucoregulatory hormones, which indicate an
  inability to maintain blood glucose, and these
  hormonal changes can be an important sign of
  impending fatigue.
• The increase in EPI, cortisol, glucagon and GH,
  along with a reduction in insulin, may contribute
  to fatigue. Carbohydrate feedings during exercise
  can blunt these glucoregulatory hormone
  responses, and, in part, this may be responsible
  for delayed onset of fatigue.
• Every 15-20 min during prolonged exercise,
  athletes should drink 8-12 oz (240-350 ml) of a
  sports drink containing carbohydrate to replace
  carbohydrate and fluid. This will prevent a fall
  in blood glucose and will likely delay fatigue.
• The delay in fatigue under these circumstances
  may involve both central and peripheral
  mechanisms.

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SPORTS SCIENCE EXCHANGE GLYCEMIC INDEX AND
EXERCISE METABOLISM SSE64-Volume 10 (1997),
Number 1

• Janet Walberg Rankin, Ph.D.Dept. of Human
  Nutrition, Foods, and ExerciseVirginia
  TechBlacksburg, VA

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Fuel Utilization During Exercise

• Carbohydrate use increases during exercise?

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Fuel Utilization During Exercise

• Goal during exercise is to maintain carbohydrate
  supply to the muscle and at the same time slow
  its depletion by relying more on fat.

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Fuel Utilization During Exercise

• What affect does insulin have on carbohydrate use
  and fat use?

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Fuel Utilization During Exercise

• Does consuming carbohydrates before and or during
  exercise improve performance?

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The Big Question

• Do certain foods provide sufficient carbohydrate,
  minimally affect insulin, and also promote fat
  use for energy?

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Types of Carbohydrate Foods

• Monosaccharide
• Fructose, Glucose, and Galactose
• Disaccharide
• Sucrose, Lactose, and Maltose
• Polysaccharide
• Starches
• Amylose straight chain
• Amylopectin branched chain

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DIGESTION
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DIGESTION

• Small intestine
• Glucose and galactose are actively transported
  from the S.I. into the blood stream
• Fructose is absorbed into the blood stream
  passively
• The liver converts most all carbohydrates
  eventually into what?

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GLYCEMIC RESPONSE

• Researchers used to think
• Complex carbohydrates (breads, cereals,
  vegetables and foods high in starch) were
  digested slowly and caused little change in blood
  glucose levels.
• Simple carbohydrates (fruit juice and high-sugar
  foods and beverages) caused blood glucose levels
  to rapidly rise and then drop precipitously.
• However, digestion and absorption do not occur at
  the same rates for all carbohydrates

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GLYCEMIC RESPONSE

• What is the glycemic index?
• The degree of increase in blood glucose levels
  after consumption of a food.
• The GI for a particular food or combinations of
  foods is determined by comparing the blood
  glucose response within a two-hour time period
  following ingestion of 50 g of that food.

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GLYCEMIC RESPONSE

• A GI of 70 indicates the consuming 50 g of the
  food provokes an increase of blood glucose 70 as
  great as that for ingesting 50 g of glucose.
• GI tends to be lower for foods that have a high
  fructose content, exhibit high amylose/amylopectin
  ratios, are present in relatively large
  particles, are minimally processed, and are
  ingested along with fat and protein.

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BEFORE EXERCISE

• Goal
• Elevate blood glucose but not insulin
• Avoid hypoglycemia
• Stimulate lipolysis

• Sherman (1991) found that the hypoglycemia
  response may not affect performance

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BEFORE EXERCISE

• Since fructose has a low GI, is it more effective
  in preventing hypoglycemia and thus improving
  performance?
• Fructose studies
• Fructose shows less insulin response
• Some studies show a glycogen sparing affect with
  fructose and maltodextrin mixed
• No performance advantage with fructose
• Reports of gastrointestinal distress with fructose

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BEFORE EXERCISE

• What about the effects of other types of
  carbohydrate?
• Starch
• Lower GI index but no benefit
• Adding fat or protein
• Lower GI index with a slight performance benefit
• Whole foods
• Those with a lower GI (milk, rice, spaghetti,
  oats) show some benefit while others (lentils)
  did not

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BEFORE EXERCISE

• What is recommended?
• Consumption of lower GI foods 30-60 min prior to
  an endurance exercise bout tends to promote the
  following effects during exercise
• Minimizes the hypoglycemia that occurs at the
  start of exercise.
• Increases the concentration of fatty acids in the
  blood.
• Increases fat oxidation and reduces reliance on
  carbohydrate fuel.
• But, it may not improve performance.

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DURING EXERCISE

• How long would a person need to exercise before
  needing to consume carbohydrates during exercise?

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DURING EXERCISE

• Why would the GI index of a food be less
  important when eaten during as opposed to before
  exercise?
• The insulin response to carbohydrate ingestion is
  suppressed during exercise.
• Fructose tend to maintain glucose and increase
  reliance on fats but does not improve performance

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AFTER EXERCISE

• Why is carbohydrate intake important after
  exercise?
• Glycogen synthesis
• Is a high or low GI food best?
• High GI foods greater glycogen synthesis
  particularly

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AFTER EXERCISE

• What is the value of consuming protein after
  exercise?
• Increase muscle synthesis
• Does the protein affect the GI? Insulin?

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CHRONIC DIET

• What about between exercise? Is there an
  advantage to high, moderate, or low GI foods?
• High GI foods increases carbohydrate oxidation
  and increases muscle storage of fat and glycogen.
• Low GI foods improves glucose tolerance
• Low GI foods increase satiety and make it easier
  to control food intake
• Low GI diets help to lower LDL-cholesterol

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PRACTICAL APPLICATIONS

• Carbohydrate intake is valuable for active
  individuals
• Low GI foods (e.g. fruits, pasta, rice, and
  legumes) before exercise.
• The GI has little effect during exercise.
• High GI foods after exercise particularly if the
  recovery period is less than 20 hours

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SPECFIC RECOMMENDATIONS
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CARBS BEFORE EXERCISE

• CARBOHYDRATE LOADING
• Increase carbohydrate intake to 70
• Taper workouts
• Not necessary unless the activity will be longer
  than 90-120 minutes.
• More beneficial in cyclists than runners.

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CARBS BEFORE EXERCISE

• EXERCISE LESS THAN 1 HOUR
• 1 hour before 1g per pound of low glycemic CHO
• High glycemic index greater insulin response
• Low glycemic index to avoid hypoglycemia during
  exercise

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CARBS BEFORE EXECISE

• EXERCISE LONGER THAN 1 HOUR
• 1- 4 hours before high CHO meal
• 2 grams of carbohydrate per pound
• Limit fat and protein intake
• 1 hour before 1g per pound of low glycemic CHO
• Avoid hypoglycemia
• Optional 50-60 grams of LGI CHO immediately
  before
• Liquid form e.g. sport drink

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CARBS DURING EXERCISE

• EXERCISE LESS THAN 1 HOUR
• High carbohydrate pre-exercise meals
• High CHO snack (bagel, banana, etc.) about 1 hour
  before exercise

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CARBS DURING EXERCISE

• DISCONTINUOUS EXERCISE
• High-carbohydrate, pre-exercise meals improve
  exercise capacity.
• Sports drinks during exercise.
• May need to consume gt100 calories per hour
• Sports drinks during prolonged exercise helps
  delay the deterioration in motor skills.

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CARBS DURING EXERCISE

• EXERCISE LONGER THAN 1 HOUR
• Drink or eat every 15-30 minutes during exercise
  or breaks
• 30-60 grams per hour
• 120-240 kcals per hour
• High glycemic index CHO
• Liquid
• 8 ounces sport drink
• 56-72 calories)
• Solid
• Energy gels 100 calories
• Candy
• Fruit

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CARBS DURING EXERCISE
Power output (intensity level) with and without
carbohydrates during exercise
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CARBS AFTER EXERCISE

• NEEDS
• Replace glycogen in muscles and liver
• Protein for muscle repair

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CARBS AFTER EXERCISE
Competing with and without adequate carbohydrates
during recovery
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AFTER EXERCISE

• CARBOHYDRATES PROTEIN
• A total of 50-100 grams of CHO and 10-20 grams of
  protein.
• Repeated with a 31 ratio of CHO protein every
  1-2 hours until next meal