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Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Chapter 4Lecture Slides

Dietary Carbohydrates

• One of the most important nutrients in your diet, from the standpoint of both health and athletic performance, is dietary carbohydrate.

What are the different types of dietary carbohydrate?

• Carbohydrates– Carbon, hydrogen and oxygen

• Simple carbohydrates– Monosaccharides

• Name them

– Disaccharides• Name them and the monosaccharides for each

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Figure 4.1

Types of carbohydrate

• Complex carbohydrates– Polysaccharide– Glucose polymer

• Total fiber– Dietary fiber

• Nondigestible carbohydrates and lignin• Intrinsic and intact in plants• Definition includes accompanying phytochemicals

– Functional fiber• Nondigestible carbohydrates with beneficial health effects• Extracted from foods; may be added to other foods

Types of dietary carbohydrate

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What are some common foods high in carbohydrate content?

Other sources of carbohydratesAdded sugars

How much carbohydrate do we need in the diet?

• Recommended Dietary Allowance (RDA)– 130 grams

• Acceptable Macronutrient Distribution Range (AMDR)– 45-65% of energy intake

• Daily Value (DV)– 60% of daily energy needs– 300 grams on a 2,000 Calorie diet

– 25 grams of fiber

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Recommended carbohydrate in the diet?

• Adequate Intake (AI) for total fiber– Men

• 38 grams up to age 50• 30 grams over age 50• DV not adequate

– Women• 25 grams up to age 50• 21 grams over age 50

Fiber in food

Recommended carbohydrate in the diet?

• Recommendations for added sugars– NAS: ≤25% of total Calories– Health professionals: ≤10% of total Calories

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Recommended carbohydrate in the diet

• Sport nutritionists– Recommend high end of AMDR– 60-70% or higher– Diet containing 3,000 Calories

• 450 grams of carbohydrate at 60% level

Metabolism and Function

• Digestion – Enzymic activity

• Absorption– Diffusion– Facilitated diffusion– Active transport

Figure 4.4

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Figure 4.5

How are dietary carbohydrates digested and absorbed and what are some implications for

sports performance?• Enzymic activity

• Some implications for sport– Rate of gastric emptying

– Multiple receptors for monosaccharides– Sodium-glucose co-transport

– High concentrations of simple sugars– Gas producing carbohydrate foods

What happens to the carbohydrate after it is absorbed into the body?

• Most dietary carbohydrates eventually are converted to glucose which circulates in the blood

• Carbohydrate foods have different effects on blood glucose levels

• The glycemic index and glycemic load

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The Glycemic Index (GI)

• The glycemic index (GI)– A ranking system relative to the effect consumption of 50

grams of a specific carbohydrate has on blood glucose – The blood glucose response to 50 grams of glucose is

ranked at 100

• GI rating scale– 70 or more – High GI foods

– 69-55 – Medium GI foods– 55 or less – Low GI foods

The Glycemic Load (GL)• The glycemic load (GL)

– A ranking system relative to the effect consumption of carbohydrate has on the blood glucose level, but incorporates the portion size, such as 4 ounces. The GL is calculated by the following formula:

Glycemic index and glycemic load

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Glycemic index and glycemic load

Glycemic index and glycemic load

What is the metabolic fate of blood glucose?

• Normal blood glucose = 80-100 mg/dL , or 80-100 milligram percent

• High GI or GL foods may lead to hyperglycemia (>140 mg/dl)

• Insulin response– Move blood glucose into body cells– May be a reactive hypoglycemia (<40-50 mg/dl)

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Insulin and GLUT-4 receptors

Insulin and GLUT-4 receptors

Fates of blood glucose

• May be used for energy

• May be converted to liver or muscle glycogen

• May be converted to and stored as fat in adipose tissues

• May be excreted in the urine if in excess

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Figure 4.6

How much total energy do we store as carbohydrate?

• Expressed as millimoles in scientific journals

Carbohydrate storage in the body

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Can the body make carbohydrates from protein and fat?

• The process of gluconeogenesis

• From protein metabolism– Glucose-alanine cycle– About 0.56 g glucose from 1 g protein

• From fat metabolism– Glycerol (about 10% or triglyceride)

– 1.0 g of glucose from 1 g glycerol

• From by-products of carbohydrate metabolism– Lactate and the Cori cycle– 0.5 g glucose from 1 g lactate

Figure 4.8

What are the major functions of carbohydrate in human nutrition?

• To supply energy– Essential for brain metabolism

– Very important fuel for many sports

• Other functions– Glycoproteins

• Ribose in DNA and RNA

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Figure 4.9

Carbohydrates for Exercise

• Carbohydrate as an energy source during exercise

• Effect of training on carbohydrate metabolism

• Methods of providing carbohydrate– Before competition– During competition– After competition

– During training

In what type of activities does the body rely heavily on carbohydrate as an energy source?

• Carbohydrate contributes about 40% of energy needs at rest

• Fat is main energy source during low exercise intensity, such as 40-50% VO2max

• Carbohydrate is major source during – Very high intensity anaerobic exercise– High intensity (>65% VO2max) aerobic exercise– Prolonged aerobic exercise events– Intermittent high-intensity exercise sports

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Why is carbohydrate an important energy source for exercise?

• May be used both anaerobically and aerobically

• Yields 5.05 Calories from one liter of oxygen

• ATP production per unit of oxygen consumed– 2.7 ATP from carbohydrate– 2.3 ATP from palmitic fatty acid

• Metabolic pathways for carbohydrate more efficient

• Muscle glycogen very important source• Liver glycogen converted to blood glucose

• Blood glucose delivered to muscles

Carbohydrate sources for exercise

• Muscle glycogen is a very important source

• Liver glycogen is converted to blood glucose

• Blood glucose is delivered to muscles

What effect does endurance training have on carbohydrate metabolism?

• Endurance training has several beneficial effects on exercise metabolism– Increase in VO2max– Increase in ability to exercise at a higher % of VO2max

without fatigue

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Exercise training and carbohydrate metabolism

• Effect on lactic acid production– Decrease production during standardized exercise– Increased clearance by liver, heart and active muscles

• Increase in insulin sensitivity of muscles– More glycogen is stored in the muscle

• Muscle increases its capacity to oxidize carbohydrate– Increase in GLUT-4 transporters– GLUT-4 receptors kept in reserve until needed; then

translocated to the cell membrane

• As noted in chapter 5, the body also increases its ability to oxidize fat during exercise

How is hypoglycemia related to the development of fatigue?

• Gluconeogenesis cannot keep pace with glucose utilization during prolonged, high-intensity aerobic exercise

• Depletion of liver glycogen eventually leads to hypoglycemia– Normal blood glucose (80-100 mg/100ml)– Hypoglycemia (,45 mg/100ml)

• Hypoglycemia can impair functioning of the central nervous system, the brain– Feelings of weakness, fatigue

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Hypoglycemia

• The human body attempts to prevent hypoglycemia

• Hormone activity– Insulin – Epinephrine– Glucagon– Cortisol

Hormones and glucose metabolism

Hormones and glucose metabolismHormone 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 bloodglucose

Promotes glycogen breakdown and glucose release from the liver

Cortisol Adrenal Exercise stress; decrease in blood glucose

Promotesbreakdown of protein; stimulates gluconeogenesis

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How is lactic acid production related to fatigue?

• Lactic acid production is associated with high-intensity anaerobic exercise

• The current thinking is that the dissociated hydrogen ion and increased acidity, not lactate itself, is the cause of fatigue

• Lactate may be used as fuel during exercise– The lactate shuttle – George Brooks– Lactate shuttles from white muscle to oxidative red muscle

• Sports drink - Polylactate

How is low muscle glycogen related to the development of fatigue?

• Low muscle glycogen and aerobic exercise– Muscle glycogen is the primary fuel for endurance

athletes, such as marathon runner

• Studies have shown physical exhaustion to be associated with very low muscle glycogen levels. However, other studies have shown fatigue with some muscle glycogen remaining.

Muscle fatigue in aerobic exercise withsome glycogen remaining

• Suggested mechanisms– Location: Glycogen may be located in the muscle fiber

where it cannot be used– Rate of energy production: Not enough glycogen for

millisecond energy needs– Muscle fiber type: May be depleted in type I; type II fibers

require more mental effort to recruit– Use of fat for energy: Muscle may need to rely on fat,

which is less efficient as an energy source– Role of the brain: Low muscle glycogen may send a signal

to the brain

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Low muscle glycogen andanaerobic exercise

• Low muscle glycogen may not impair high-intensity anaerobic exercise if there is adequate glycogen in the white muscle fibers

• Prolonged anaerobic exercise, such as 3 minutes, may be adversely affect by low muscle glycogen in the fast twitch fibers

• Field research suggests muscle glycogen depletion in fast twitch muscle fibers may contribute to slower sprint speeds in the latter states of high-intensity intermittent exercise sports, such a soccer.

How are low endogenous carbohydrate levels related to the central fatigue hypothesis?

• The central fatigue hypothesis– Low muscle glycogen and blood glucose will stimulate

gluconeogenesis from protein– Branched chain amino acids (BCAA) are a main source– Blood levels of BCAA decline– As BCAA levels drop, free tryptophan (fTRP) increases– A high fTRP:BCAA ratio favors entry of fTRP in the brain

– Brain TRP increases serotonin, which is related to fatigue symptoms

• Adequate carbohydrate will help prevent the decline in BCAA

Central fatigue hypothesis

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Will eating carbohydrate immediately before or during an event improve physical performance?

• Endogenous carbohydrates– Importance of initial body stores– Adequate for 60-90 minutes of aerobic exercise

• Exogenous carbohydrate– To help improve performance, exogenous carbohydrate

intake must be able to delay the onset of fatigue that would otherwise occur as a result of premature depletion of endogenous carbohydrate sources.

– Other factors may explain beneficial effects of exogenous carbohydrates; research with oral sensation

Effects of exogenous carbohydrate on exercise performance of different intensity and duration

• Very high-intensity exercise for < 30 minutes– In general, no effect– May benefit athletes in weight-control sports

• Very high-intensity resistance exercise training– In general, no

• High-intensity exercise for 30 to 90 minutes– In general, no– Some studies show benefits; possibly beneficial effects on

the central nervous system; sprint performance in an overall aerobic event

Exogenous carbohydrate and performance:Exercise intensity and duration

• Intermittent high-intensity exercise for 60-90 minutes– Some studies show beneficial effects on performance,

particularly in the latter stages of the protocol– Some beneficial effects from field studies

• High- to moderate-intensity exercise greater than 90 minutes– Generally, research supports a beneficial effect– Maintain blood glucose concentrations to help sustain high

rates of carbohydrate oxidation

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Timing of carbohydrate intake

• Four hours or less before exercise– Possible beneficial effects if taken 1-4 hours before

• Less than 1 hour before exercise– Research findings somewhat ambiguous

• Possibility of reactive hypoglycemia in some athletes• Most studies show no adverse effects• May have some beneficial effects

Timing of carbohydrate intake

• Immediately before exercise– Not beneficial if exercise is short in duration– May benefit performance in more prolonged aerobic

endurance events > 60% VO2max• Exercise suppresses secretion of insulin• Exercise stimulates secretion of epinephrine

• During exercise– May enhance performance in prolonged aerobic exercise– Maintains blood glucose

– Provides energy to muscles– Reduces ratings of perceived exertion

Use of ingested carbohydrate

• Exogenous carbohydrate may be used as an energy source within 5-10 minutes

• Peak use appears to occur 75-90 minutes after ingestion

• May contribute 20-40 percent of the carbohydrate energy source during, or more in the latter stages of exercise

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Possible fatigue-delaying mechanisms

• Maintenance of blood glucose levels– Most likely mechanism– Prevent hypoglycemia– Glucose provided to muscle cells

• Reduction of psychological effort– Glucose provides energy to the brain– Prevent decrease in BCAA– Reduce RPE (ratings of perceived exertion)

Possible fatigue-delaying mechanisms

• Sparing of muscle glycogen– Research findings equivocal

• Positive effects: Spared muscle glycogen in slow-twitch muscle fibers

• Negative effects: No glycogen sparing even when subjects were maintained hyperglycemic with glucose infusions

Limitations to prevent fatigue

• It appears that the maximal amount of oxidizable exogenous carbohydrate provided during exercise is 1.5 to 1.7 grams per minute, or lower.

• This is much lower than the required energy needs at 65-85% of VO2max. Elite runners might oxidize 4-5 grams of carbohydrate per minute.

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Optimal supplementation protocol

• Consume carbohydrates both before and during the exercise task.

When, how much, and in what form should carbohydrates be consumed before or during exercise?

• Athletes who may benefit from carbohydrate intake– Endurance exercise– Intermediate high-intensity exercise

• Fluid replacement is also an important consideration

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Pre-exercise:When and how much?

• 4 hours prior to event– 4-5 g CHO/kg body weight– 70 kg athlete: 280-350 grams of carbohydrate

• 1 hour prior to event– 1-2 g CHO/kg body weight– 70 kg athlete: 70-140 grams of carbohydrate

• Immediately before exercise– 50-60 grams in a concentrated form

• Some commercial sport/energy drinks

During exercise: When and how much

• When?– About every 15-20 minutes

• How much?– Approximately 1 gram per minute, or about 60 grams an

hour

Some general recommendations

Asker Jeukendrup, University of Birmingham

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Carbohydrate Intake before Competition

• 4 hours prior– 4-5 grams/kg– Some lean protein

• 1 hour prior– 1-2 grams/kg

• Immediately before– 1 gram/kg

• 4 hours before• 70 kg runner• 280-350 grams

– Large bagel (75g)– Turkey breast (0g)

• 4 oz (28 g protein)

– Orange juice (45 g)• 12 oz

– Yogurt, fruit (50g)• 8 oz

– Banana (30g)– Energy drink (80g)

• 12 oz

Types of carbohydrateCarbohydrate combinations

• Carbohydrate combinations, such as glucose and fructose

• Use different receptors for absorption• Up to 1.2-1.7 gram per minute may be used, or 72-

102 grams per hour

• May be useful when more than 60 grams per hour is recommended

Separate receptors for monosaccharides

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Types of carbohydrateFructose

• Fructose theorized to be better than glucose because it is absorbed more slowly, leading to a blunted insulin response and a more stable blood sugar

• However, effect when ingested before or during exercise is little different from glucose

• Large amounts may cause diarrhea

Types of carbohydrateSolid and liquid carbohydrates

• Sport drinks; sport gels; sport jelly beans

• Appears to be little difference between the two forms relative to the effects on performance

• Preference of the athlete should be considered

Types of carbohydrateLow-glycemic-index foods

• Similar theory as fructose; low-GI foods may help maintain a higher blood glucose level

• Numerous studies show no significant differences between low-GI and high-GI diets on exercise performance

• However, several recent studies from Loughborough University show some beneficial effects, such as greater run time to exhaustion at 70% VO2max with a low GI (GI = 37) versus a high GI (GI = 77) diet

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Types of carbohydrateCarbohydrate with protein

• Several studies have compared the effects of carbohydrate supplementation alone to carbohydrate/protein supplementation on performance following recovery from previous exercise.

• In general, there is little difference between the treatments on subsequent performance

Types of carbohydrateIndividuality

• Some athletes more vulnerable to gastrointestinal distress with various forms or concentrations of carbohydrate– Runners are prone to “Runner’s trots” with highly

concentrated solutions

• Experiment with different types and amounts of carbohydrate for your event

• Train your stomach as you train your muscles; know your limits

What is the importance of carbohydrate replenishment after prolonged exercise?

• Rapid restoration of muscle glycogen important for some athletes– Repeated bouts of prolonged, intense exercise on the

same day– Prolonged, intense exercise on consecutive days

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Carbohydrate replenishment after prolonged exercise

• In repeated bouts of prolonged, intense exercise with 4-hour interval– Consume 1 gram/kg body weight immediately after first

event, and also 2 hours prior to the second event. May also consume carbohydrate immediately before and during the second event

Carbohydrate replenishment after prolonged exercise

• In repeated bouts of prolonged, intense exercise on consecutive days– Consume about 1.2 to 1.5 grams of carbohydrate per kg

body weight every hour for 4-5 hours after exercise. Carbohydrate snacks may be eaten every 30 minutes.

Carbohydrate and protein replenishment after prolonged exercise

• Some early research suggested combining carbohydrate with protein would increase muscle glycogen resynthesis.

• However, recent research indicates that if equivalent energy from carbohydrate and carbohydrate/protein supplements are provided, there is no additive effect of the protein.

• As noted in chapter 6, providing protein after exercise may provide some benefits.

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Carbohydrate-rich diets for athletes

• Sport nutritionists recommend that athletes consume about 8-10 grams of carbohydrate per kilogram body weight daily

• For a 70-kg athlete, this would amount to 560 to 700 grams of carbohydrate daily, or the equivalent of 2,240 to 2,800 Calories

• On a 3,500-Calorie daily intake, the carbohydrate would provide 65-80% of daily energy intake.

• This amount of daily carbohydrate would help restore muscle glycogen levels

Will a high-carbohydrate diet enhance my daily training?

• Per kg body weight, sport nutritionists generally recommend about 5-7 grams of carbohydrate daily for athletes in general training, and about 7-10 for endurance athletes

• Research suggests high-carbohydrate diets may help training both physiologically and psychologically,

• Not all athletes need very high carbohydrate diets. Even some elite trained endurance athletes may sustain training on lower amounts, but training may be more stressful psychologically.

Carbohydrates during training

• There is no evidence that low-carbohydrate diets improve exercise performance

• A diet rich in healthy carbohydrates may help guarantee optimal energy sources for daily training

• Train high and compete high is the concept of training and competing with high carbohydrate intake.

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Carbohydrate Intake During Training

• Consume a healthy diet at the high end of the AMDR for carbohydrates, or about 60-70% or more of energy from carbohydrate.

• Focus on meals with a low glycemic load

• Carbohydrates should fill about 2/3 of your plate during meals.

• Snacks should be rich in carbohydrates

Carbohydrate Intake During Training

• Some athletes may continue to train effectively with somewhat lower carbohydrate diets, approximating 45% of energy intake.

• Some recent research suggests training with low glycogen stores may induce gene expression that may enhance training adaptations

• However, ratings of perceived exertion (RPE) may be higher during training with low carbohydrate intake. Research is too limited to recommend training with low carbohydrate diets.

Carbohydrate Intake During Training

• In general, consume about 6-10 grams of carbohydrate per kilogram body weight, or about 3-5 grams per pound body weight. (1 kilogram = 2.2 pounds).

• If you train less than 1 hour/day, then about 6-7 grams is sufficient. As your daily training time increases, consume 8-10 grams or more per kilogram body weight.

50 kg50 kg110 lbs110 lbs

55 kg55 kg121 lbs121 lbs

60 kg60 kg132 lbs132 lbs

65 kg65 kg143 lbs143 lbs

70 kg70 kg154 lbs154 lbs

75 kg75 kg165 lbs165 lbs

80 kg80 kg176 lbs176 lbs

85 kg85 kg187 lbs187 lbs

90 kg90 kg198 lbs198 lbs

66--7 7 g/kgg/kg

300300toto

350350

330 330 to to

385385

360360to to

420420

390390toto

455455

420 420 to to

490490

450 450 to to 525525

480 480 to to

560560

510510to to

595595

540 540 toto630630

88--10 10 g/kgg/kg

400 400 to to

500500

440 440 to to

550550

480 480 to to

600600

520 520 to to

650650

560 560 to to

700700

600 600 to to

750750

640 640 to to

800800

680 680 to to

850850

720 720 to to

900900

Recommended daily carbohydrate intake, in grams, for endurance athletes.

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Carbohydrate Intake during Training• Dietary strategies for rapid muscle glycogen restoration

– Consume carbohydrates immediately after and about every 30 minutes for 4-5 hours post-exercise

– Consume about 0.6 to 0.8 gram per kilogram body weight – Consume carbohydrates with a high glycemic index– Consume as either liquids or solids– Consume some lean protein as well. The carbohydrate:protein ratio

should be about 4:1, or 4 grams of carbohydrate for each gram of protein.

– This full procedure is not necessary if there is ample time for full recovery, but consuming a carbohydrate:protein combination immediately after exercise is recommended.

Carbohydrate loadingWhat is carbohydrate, or glycogen, loading?

• Method of increasing muscle glycogen levels– Also known as muscle glycogen supercompensation

What type of athlete would benefit from carbohydrate loading?

• Athletes who sustain high levels of continuous energy expenditure for prolonged periods– Long-distance runners– Cross-country skiers– Endurance triathletes– Tournament play in intermittent high-intensity exercise

sports

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How do you carbohydrate load?

• Athlete should be fully trained• Classic procedure not necessary:

– Depletion stage– Low carbohydrate diet– Carbohydrate loading

• Have about 3-4 days of high carbohydrate intake, about 8-10 grams/kg body weight, or more

• Low and high glycemic index carbohydrates are equally effective• Taper exercise training over the course of a week or longer

Carbohydrate loading procedures

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Will carbohydrate loading increase muscle glycogen concentration?

• Most studies report increased muscle glycogen levels following carbohydrate loading procedures

• Both males and females will increase glycogen levels if adequate energy and carbohydrate are consumed

• Muscle glycogen levels may increase two to three times above normal

• Experiment with the protocol during training

How do I know if my muscles have increased their glycogen stores?

• Monitor changes in body weight

• Approximately 3-4 grams of water are bound to each gram of muscle glycogen

• An additional 300-400 grams of glycogen plus 900-1,200 grams of water is 1,200-1,600 grams, or 2.5-3.5 pounds above your normal weight

• Bodybuilders may use this technique to highlight muscle definition, but research is not supportive of its effects

Will carbohydrate loading improve exercise performance?

• In general, the procedure is not needed for exercise tasks of short duration

• In general, research supports the use of carbohydrate loading as a means to enhance performance in prolonged endurance exercise tasks– Helps maintain an optimal pace longer– Extra body water may help during exercise in the heat

• Most appropriate protocol is to use both carbohydrate loading and consumption of carbohydrate during the event

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Are there any possible detrimental effects relative to carbohydrate loading?

• The extra body weight could be a disadvantage in running, but this appears to be offset by the increased energy supply. The water may also be beneficial during exercise in the heat.

• Diabetics should consult their health professional• Low-GI foods may be more healthful for some

• High amounts of simple sugars may contribute to gastrointestinal distress

Carbohydrates: Ergogenic Aspects

• Metabolic by-products

– Pyruvate

– DHAP (Pyruvate and dihydroxyacetone)– Lactate salts

– Ribose– Multiple carbohydrate products

Pyruvate

• Pyruvate is a 3-carbon by-product of glycolysis

• Theory: Accelerate the Krebs cycle or use glucose more effectively

• Efficacy– Research is limited, but the available research indicates

that supplementation with pyruvate does not enhance endurance performance.

– Several studies have shown beneficial effects on weight loss in obese subjects

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DHAP

• Dihydroxyacetone is also a 3-carbon carbohydrate

• Theory: Increase muscle glycogen content

• Efficacy– Although several studies have shown that DHAP

supplementation might enhance aerobic endurance performance in untrained males, no studies are available with trained individuals.

Lactate salts

• Lactate is a small metabolite of glucose; C3H5O3

• Converted to pyruvate or glucose

• Found in a sports drink– CytomaxTM

– Contains alpha-L-polylactate plus fructose, glucose, and glucose polymer

• Research limited and equivocal

• Additional research with CytomaxTM recommended

Ribose

• Ribose is a 5-carbon monosaccharide– Very little ribose consumed in a normal diet– Produced naturally in the body– Found in RNA and ATP

• Theory: Rapid resynthesis of ATP

• Efficacy: The current data do not support an ergogenic effect of ribose supplementation. – Anaerobic cycle ergometer performance

– Peak power output– Maximal knee extension– 2,000-meter rowing performance

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Multiple carbohydrate by-products

• Contain intermediates of the Krebs cycle

• Limited research, but no beneficial effects on exercise performance or recovery

Dietary CarbohydratesHealth Implications

• Recommendations

– Eat more of the good carbs• Complex carbohydrates• Total fiber

– Eat less of the bad carbs• Added sugars

• Highly processed and refined carbohydrates

How do refined sugars and starches affect my health?

• High intake of refined carbohydrates has been alleged to contribute to a number of health problems– Psychological behavior

• Hyperactivity in children• PMS

– Dental caries• Inflammation may become systemic

– Cancer – Diabetes

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Refined sugars and starches and health• NAS indicated that given the currently available scientific

evidence relative to the effect of dietary sugar on dental caries, psychological behavior, cancer, risk of obesity and hyperlipidemia, there is insufficient evidence to set an UL

• Nevertheless, the NAS did note the theory linking a high-GI diet to certain health problems appears to be valid. It did not set an UL, but recommended a maximum of 25% of energy intake.

• Some health professional organizations recommend less than 10% of energy intake.

Decreasing intake of refined carbohydrates

• Eat refined starches and grains sparingly. Use mainly as a side dish

• Read food labels and select foods low in sugar• Reduce the sugar in foods prepared at home

• Eat more fruits for naturally occurring sugars

• Decrease intake of soft drinks• Use other sweeteners such as cinnamon, ginger or

artificial sweeteners

Are artificial sweeteners safe?

• Products available– Saccharin

– Aspartame– Neotame

– Sucralose– Sugar alcohols

• Sorbitiol, erythritol, mannitol

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Artificial sweeteners

Artificial sweeteners

• Recent reviews by the FDA and Consumers Union consider all artificial sweeteners to be safe in small amounts.

• May be helpful in weight control

• Some caveats:– Aspartame and individuals with phenylketonuria

– High intakes of sugar alcohols may cause diarrhea

Why are complex carbohydrates thought to be beneficial to my health?

• Healthy carbohydrates are an integral part of several healthy diet plans– Dean Ornish diet plan; the Pritikin program

– The OMNI diet plan

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Healthy carbohydrates• Healthy carbohydrates

– Whole grains– Fruits– Vegetables– Legumes

• Proposed attributes of healthy carbohydrates– Low-glycemic foods– Various phytochemicals– Various vitamins and minerals

– Dietary fiber

Healthy carbohydrates

Why should I eat foods rich in fiber?

• Adequate intake (AI) for total fiber: Based on reduced risk of coronary heart disease– 14 grams per 1,000 Calories

• 38 grams for men age 18-50• 25 grams for women age 18-50

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Soluble and insoluble fiber

• The issue of soluble and insoluble fiber– Difficult to generalize on different health effects of

soluble and insoluble fiber; health effects are due to total fiber, but it may be illustrative to discuss soluble and insoluble fiber effects on health.

Proposed health benefits of fiber

• Water-insoluble fibers are considered to have the greatest effect on fecal bulk– Rapid movement through the digestive tract

• Fiber rich foods are low-GI foods– Increase insulin sensitivity

• Gummy forms of fiber may bind with certain substances in the digestive tract– Carcinogens and cholesterol

• Some water-soluble fibers may be fermented in the large intestine to SCFA– SCFA can help reduce serum cholesterol

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Health effects of dietary fiber

• May help reduce risk of heart disease

• The reduced glycemic response may be of benefit to treat or prevent diabetes

• Effect on prevention of colon cancer not as effective as once thought, but some proposed more long-term studies are needed

Do some carbohydrate foods cause food intolerance?

• Lactose intolerance– Lactose found in milk and dairy products

– Individuals with low levels of lactase– Gastrointestinal symptoms

– Need to find alternative source of calcium• Fermented daily products (Yogurt)• Dark, green leafy vegetables

• Calcium fortified products (orange juice)• Calcium supplements

Example of daily food intake to obtain fiber AI

Foods Grams of fiber

3 fruits 6

3 vegetables 9

3 slices of whole grain bread 6

½ cup beans 7

1 serving bran cereal 9

Total daily fiber intake 37

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Gluten intolerance

• Gluten is a protein found in wheat, rye and barley; the immune system recognizes gluten as a foreign substance

• Symptoms may be mild, primarily gastrointestinal distress

• In severe cases, celiac disease causes damage to the lining of the small intestine; medical treatment is necessary

Does exercise exert any beneficial effects related to carbohydrate metabolism?

• Exercise may enhance glucose tolerance and insulin sensitivity– Glucose uptake in body cells is elevated for two hours after

an endurance exercise bout• Effect is insulin-independent• May increase GLUT-4 receptors in cell membranes

– Exercise can increase insulin sensitivity for 16 hours afterwards

– Exercise believed to be important in the prevention of type 2 diabetes