Carbohydrates Chapter 5. What are Dietary Carbohydrates? Organic compounds containing –Carbon...
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Transcript of Carbohydrates Chapter 5. What are Dietary Carbohydrates? Organic compounds containing –Carbon...
What are Dietary Carbohydrates?
• Organic compounds containing– Carbon– Oxygen– Hydrogen
– CH2O
• Formed naturally in nature
• Synthesized
• ~4 kcal/gram
Types of Carbohydrates
• Simple CHO– Monosaccharides
• Glucose (dextrose, grape sugar)• Fructose (levulose, fruit sugar)• Galactose (milk sugar)
– Disaccharide• Maltose (malt sugar, glucose & glucose)• Lactose (milk sugar, glucose & galactose)• Sucrose (cane or table sugar, glucose & fructose)
CHO Types
• Complex CHO– 3 or more glucose molecules– Polysaccharide (>2 molecules)
• Plant starches • Animal starch (glycogen)• glucose polymer (10-20 molecules)
– Maltodextrin– polycose
– Fiber
Plant Starches
• Contains many (up to several thousand) monosaccharides
• Storage form of CHO in plants• Types
– Amylopectin – branched-chain molecule that is rapidly digested and absorbed
– Amylose – long chain molecule that is more slowly digested and absorbed
• Most starches contain combinations of both
Concentration Units
• Mole = gram molecular weight• A mole is the weight in grams of a
particular substance, like glucose• Example
– Glucose is C6H12O6
– Atomic weight of C is 12, H is 1, O is 16– Multiply the atomic weight X the number of
that element in the molecule and sum it up.- 1 mole glucose is 180 grams
Muscle Glycogen Units
• Muscle glycogen/glucose concentration are expressed per kg of dry weight (d.w.) or per kg of wet weight (w.w.)
• In muscle, w.w. x 4.5 = d.w.
• Normal Muscle Concentration– 12-16 g/kg w.w or 1.7 g/100 g muscle– 65-90 mmole/kg w.w– Can be ~ doubled by carbo loading
Liver Glycogen Units
• Normal liver glycogen is 50-75 g/kg w.w.• Liver glycogen reduced by 50% after 1
hour of exercise at 75% VO2max. • At rest, glucose output is 150 mg/min
– 60% from liver glycogen– 40% from gluconeogenesis
• At >75% VO2max– Glucose output is 1 g/min– 90% from glycogen
TABLE 4.7 Major hormones involved in regulation of blood glucose levels
Hormone Gland Stimulus Action
Insulin Pancreas Increase in blood glucose
Helps transport glucose into cells; decreases blood glucose levels.
Glucagon Pancreas Decrease in blood glucose; Exercise stress
Promotes gluconeogenesis in liver; helps increase blood glucose levels.
Epinephrine Adrenal Exercise stress; decrease in blood glucose
Promotes glycogen breakdown and glucose release from the liver: helps increase blood glucose levels
Cortisol Adrenal Exercise stress; decrease in blood glucose
Promotes breakdown of protein and resultant gluconeogenesis; helps increase blood glucose levels
Causes of Muscular Fatigue Related to CHO Use
• Muscle Glycogen Depletion– Fatigue begins to occur at approx 30-40
mmole/kg ww.– Short duration high intensity (<60 sec) not
affected until glycogen drops below 20 mmole/kg
– Normal glycogen levels – 60-90 mM/kg– Max levels – 200 mM/kg
Causes of Fatigue Continued
• Liver Glycogen Depletion– Normal glycogen range: 250-300 mM/Kg– At rest, glucose from liver is 150 mg/min
• 60% from liver glycogen• 40% from gluconeogenesis
– During exercise at 75% VO2max, output is 1 gm/min with 90% from glycogen.
– Normoglycemia: 60-100 mg/dl– Hyperglycemia: >140 mg/dl– Hypoglycemia: <45 mg/dl
• Reactive Hypoglycemia
Glycemic Index (GI)
The GI reflects the rate of digestion and absorption of CHO
GI =
Blood glucose area after test food
Blood glucose area after reference food
X 100
Glycemic Load
• Glycemic index relative to the serving size
• Some CHO have high GI but are consumed in small quantities per serving
• GL = (GI x CHO/serving)/100
• Ratings of glycemic loads– High GL = >20– Medium GL = 11-19– Low GL = <11
Use Of GI In Sports Nutrition
• Before Exercise: A low-GL CHO should be eaten, particularly before prolonged exercise, to promote sustained CHO availability
• During Exercise: Moderate to High-GL CHO foods or drinks are most appropriate
• After Exercise: High-GL CHO for glycogen resynthesis
Major Factors Influencing Skeletal Muscle CHO Metabolism During Exercise
• Exercise Intensity
• Exercise Duration
• Training
• Diet
Exogenous CHO Oxidation & Intensity of Exercise
• Exo CHO oxidation increases with increasing intensity up to 60% VO2max.
• Peaks at 1.0-1.1 g/min• Above 60% VO2max, increases in CHO
oxidation are due to increases in muscle glycogen oxidation up to 4 g/min
• Limitation is due to rate of digestion, absorption and transport of glucose into systemic circulation
Daily CHO Reqirements
• Minimum of 100 g/day for nervous system
• Moderate duration/low intensity training of 1-3 hours – 5-7 g/kg
• Moderate to heavy endurance training of 1-2 hours – 7-12 g/kg
• Extreme exercise of 4-6 hours – 10-12 g/kg
General Considerations
• Must get adequate overall nutrition in addition to the CHO– Vitamins and minerals– Adequate protein– Total calories
• Glycemic Index needs to be considered
Consumption 3-4 hours Before Exercise (Pre-Competition Meal)
• Up to 2-3 g/kg of CHO (200-300 gm)
• Moderate to high glycemic index CHO
• Minimal fat and protein
• Increases muscle and liver glycogen
Less Than 1 Hour Before Exercise
• Individuals prone to reactive hypoglycemia should avoid CHO, especially high glycemic CHO– May increase glycogen use
• Up to 100 g low to moderate GI if no feeding during exercise
• If feeding during exercise, then nothing up to 1 hour before.
During Exercise
• Maximal use of exogenous CHO is ~ 70 grams per hour
• Timing of feedings seem unimportant• 5-10% solution of 15-20 grams every 15-20 min
– 8 oz of Gatorade contains approx. 15 grams of CHO– High Fructose may cause stomach upset
• Multiple CHO types may increase use• Always test feeding prior to competition
After Exercise
• Glycogen resynthesis rate is about 5-7% per hour
• 2 hour window following exercise for maximal rate of resynthesis
• High glycemic foods• Combination of CHO and protein is best in
a 3:1 ratio of CHO to protein. However, if total CHO intake is sufficient, PRO doesn’t matter.
When Recovery Time is <8 hrs
• 1.2 gm/kg immediately and each hour for 4-6 hours
• Can consume in one bolus each hour or smaller quantities every 30 minutes
• If lesser amounts of CHO are available, consuming protein with CHO in 3:1 ratio is best (may also increase protein anabolism)
• CHO in fluid solution will also replace fluids
When Recovery Time is >8 hours
• Most important factor is meeting total CHO requirement if the intake is spread throughout the next 24 hours.
• However, you can’t wait until the last minute as total resynthesis takes approximately 20 hours
Factors Affecting Glycogen Resynthesis
• Trained have higher rates than untrained
• A lower starting concentration will increase the rate of synthesis
• No difference in fiber types???
• Eccentric exercise has lower rates than concentric exercise after 18-72 hours, but not up to 6 hours
• No difference in males and females
Table 4.8 CHO LoadingOriginal Classic Method
Day 1 Depletion exercise
Day 2 High-protein/fat, 15-20% CHO
Day 3 High-protein/fat, 15-20% CHO
Day 4 High-protein/fat, 15-20% CHO
Day 5 High CHO (70-80%)
Day 6 High CHO
Day 7 High CHO
Day 8 Competition
Table 4.8 CHO LoadingContemporary Recommended Method
Day 1 Depletion exercise (optional)
Day 2 Mixed diet (50-55% CHO)
Day 3 Mixed diet
Day 4 Mixed diet
Day 5 High CHO (70-80%)
Day 6 High CHO
Day 7 High CHO
Day 8 Competition
Alcohol As An Energy Substrate
• 7 kcal/gram• By-products of alcohol metabolism
released in blood appear to be of little importance to exercising muscle
• Alcohol consumed prior to exercise may contribute 5% of energy over 90 min of exercise
• Alcohol requires more O2 for metabolism than CHO or fat