Carbohydrates: The Main Energy Food

The Dietary Carbohydrates

l   Carbohydrates

l   Organic compounds that contain carbon, hydrogen and O2 in various combinations

l   Types:

l  Simple CHO’s

l   Monosaccharide
l    glucose, fructose, galactose
l   Disaccharides (2 monosaccharides)
l    Maltose (glucose + glucose)
l    Lactose (glucose + galactose)
l    Sucrose (glucose + fructose)

The Dietary Carbohydrates

l   Carbohydrates

l  Types: (continued)

l  Complex CHO’s (commonly known as starches)

l   3 or more glucose molecules combined = polysaccharide
l   More than 10 glucose molecules combined = glucose polymer (e.g. maltodextrin)
l    These are used in sports drinks

l  Dietary Fiber

l   Water soluble – dissolved in H2O & metabolized in large intestine (e.g. gums, pectins)
l   Water insoluble – not dissolved or metabolized (e.g. cellulose)

How much CHO do we need?

l    Officially, the National Research Council has not established an RDA for CHO

l    General Recommendations:

l    55-60% of total caloric intake

l   At least 50-100 grams to spare protein catabolism

l   Healthy, moderately active adults should have at least 200 grams to maintain normal brain and muscle function

l   Should be simple sugar limitation of 10% in total

l   NCI recommends 20-35 grams of fiber per day

l    60-70% of total caloric intake in endurance athletes

Metabolism and Function

l    Majority of nutrients from CHO breakdown are absorbed in small intestines

l    Glucose is primary CHO nutrient

l    Its effect is measured based upon:

l   Glycemic index – effect of a particular food upon the rate and amount of increase in blood glucose level

l    This may also vary from individual to individual
l    Baseline value is 100
l    Foods with a high glycemic index will raise blood glucose levels quickly
l    Foods with a low glycemic index will lead to a slower insulin response and more stable blood glucose level

The Glycemic Index

Glucose Levels in the Blood

l    Normal resting level

l    80-100 mg/dl (or mg%)

l    Controlled by insulin (secreted from pancreas)

l   Insulin activates GLUT-4 receptors in muscle and fat cells to cause uptake of glucose

l    Hyperglycemia

l    Blood glucose level > 140 mg%

l    May result from foods of high glycemic index

l    Hypoglycemia

l    Blood glucose level < 40-50 mg%

l    May be prompted by fast influx of insulin into blood to reduce high glucose level

Major Fates of Blood Glucose

l    Source of energy

l    Particularly for brain and nervous tissue

l    Conversion to liver or muscle glycogen

l    Liver glycogen can be converted back to blood glucose

l    Muscle glycogen does not convert back to blood glucose

l    Converted and stored as fat in adipose tissue

l    Excreted in urine when excess amounts exist

Stores for CHO in the body

Can human body make CHO from fat and protein?

l    Yes

l    Through process of gluconeogenesis

l    Formation of new glucose from non-glucose sources

l   Fats

l    Glycerol may be converted to glucose in the liver

l   Proteins

l    Alanine may be converted to glucose in the liver

l   Others

l    Pyruvate and lactate
l    Lactate converted to glucose in liver and returned to muscle

CHO functions

l   CHO provides only 15-20% of muscles energy needs at rest

l   Otherwise, supply primary energy to brain, nerves, and red blood cells

l   CHO provides building component to glycoproteins

l  Make up cell membranes

l   Serve as receptors to regulate cell function

l  Component parts to RNA

CHO and Exercise

l   CHO supplies ~40% of body’s energy needs during rest

l   During exercise, its use is regulated based upon the intensity level

l   Appropriate CHO intake is most important for endurance events lasting 90-120 minutes

l   Also important for intermittent bouts of high-intensity, e.g. soccer, rugby, hockey, tennis

Rate of CHO usage

l   The higher the intensity the greater the usage

l   Environmental conditions speed up use of CHO’s in the body:

l   High altitude

l   Hot and cold climates

Why is CHO an important energy source?

l    More efficient rapid fuel than fat

l    From 1 liter of O2, CHO yields 5.05 Calories while fat yields 4.69 Calories (i.e. you need more O2 to generate energy from fat)

l    Can produce ATP up to 3 times faster with CHO compared to fat

l    Readily available in muscle for energy needs

l    During moderate intensities, can get equal amount of energy from muscle and liver glycogen

l    During higher intensities, greater dependence on muscle glycogen

Effect of endurance training on CHO metabolism

l    Increase in VO2 max

l    Greater ability to utilize O2 to burn energy fuels

l    Can work at higher % VO2 max without fatigue

l    Won’t produce as much lactate at 60% VO2 max as you did prior to training

l    Increases glucose transporter (GLUT-4)

l    Allows for more rapid uptake of glucose and more rapid replenishment of muscle glycogen during recovery


Effect of endurance training on CHO metabolism

l   Increase muscle cell mitochondria density

l   This can accelerate metabolism of CHO in the muscle cell

l   Increases ability to use fat and spare glycogen stores in the muscle

l   More glycogen storage in the muscle

Hormonal regulation of blood glucose

Low Glycogen and Fatigue

l    Physical exhaustion has been correlated to low muscle glycogen levels

l    This results from:

l   Exercising at 65-85% or higher of VO2 max

l   Depletion of muscle glycogen in specific fiber types

l    Primarily in Type I (ST) and Type IIa (FT, oxidative+ anaerobic), during a prolonged endurance activity
l    Later dependence on Type IIb (FT, anaerobic), which increases production rate of lactic acid; changing acid-base balance
l    Low fast-twitch muscle glycogen levels may hinder performance in high intensity  and intermittent events
l    Low muscle glycogen level may be result of low CHO diet or previous exercise

Are there other mechanisms for fatigue?

l    Central fatigue hypothesis

l    Low muscle glycogen, along with low blood glucose, can stimulate gluconeogenesis

l   This prompts use of proteins to make more glucose

l    Branched-chain amino acids (BCAA) in the muscle will be catabolized for energy
l    BCAA from blood will also be taken up by muscle for energy
l    Low BCAA in blood allows less competition for tryptophan in competing for brain needs
l    Tryptophan will cause increase in brain serotonin, which results in greater fatigue sensations (or prompts the brain to slow its activities)

l   Will taking BCAA supplements lessen fatigue?

CHO intake Before and During Competition

l   Endurance events generally benefit from CHO intake before and during competition

l   General findings:

l   For very high intensity exercise of < 30 min

l  CHO supplementation does not improve performance unless muscle or liver glycogen- deficient prior to event

CHO intake Before and During Competition

l    General findings: (continued)

l    For very high intensity resistance exercise

l   CHO supplementation does not improve # of reps, even under conditions of energy restriction

l    For high-intensity exercise for 30-90 min

l   CHO supplementation does not improve performance in trained athletes, however performance of elite athletes may be improved

l    For intermittant high-intensity exercise of 60-90 min

l   CHO supplementation during endurance-type activities with intermittant bouts of sprinting (e.g. soccer, hockey, tennis) can benefit performance, primarily in latter stages of contest


CHO intake Before and During Competition

l   General findings: (continued)

l   For high to moderate-intensity exercise > 90 min

l  CHO supplementation can be improved


When are the best times to take CHO supplementation for events?

l    1-4 hours before endurance event

l    Effective in helping performance

l    Ingesting CHO during prolonged race is equally effective in helping performance

l    15-60 min prior to event

l    May cause hypoglycemic response, particularly with high-glycemic index foods

l   Results in feeling of tiredness

l    Appears to affect ¹/³  of well-trained individuals

l    Others may benefit through normal influx of glucose into muscles during exercise

When are the best times to take CHO supplementation for events?

l   Immediately (5-10 min) before endurance event

l   May delay development of fatigue if event is 2 hours or more at an intensity of 60-75% of max

l  Not enough time for reactive hypoglycemic response

l   During exercise

l   CHO supplementation is beneficial

l  Both throughout event and even if taken only during latter stages of endurance event


How quickly does the CHO intake get to us?

l   Some of the ingested CHO, just prior to exercise, has been shown to be utilized within 5-10 min of the exercise

l   Peak usage of ingested CHO occurs 75-90 minutes into the exercise

l   This will vary with individuals

l  20-40% of ingested CHO used during exercise

l  60-70% of ingested CHO used in latter stages of the event

Fatigue-delaying mechanisms of CHO

l    Extra glucose in blood:

l    Allows sparing of liver glycogen for energy

l    Does not allow sparing of muscle glycogen in moderately high intensity events of long duration

l    In prolonged events of low intensity, muscle glycogen can be spared as the muscle can readily use the blood glucose when needed

l    Reduces stress of body seeking fuel sources

l   Noted by reduced levels of perceived exertion

l    Shown to prevent decrease in BCAA so less tryptophan effect on brain (less tiredness sensation)

Can glucose ingestion prevent fatigue?

l   No

l   But it can slow the occurrence rate of fatigue

l   Energy supplied by exogenous CHO is ~ 1 gram of energy per minute

Glucose Supplementation Terms

l   Glucose-electrolyte solution (GES)

l   A fluid replacement drink to replace H2O and CHO lost during exercise

l   Sugar content range between 5-10% (~6-12 Calories per ounce)

l   Contains major electrolytes (Na, Cl, K, P)

l   Examples:

l  Gatorade, All-Sport, Mountain Dew Sport, Power Ade

Glucose Supplementation Terms

l   Glucose-polymer solution (GPS)

l   A fluid replacement drink to provide CHO while concentration of solution; minimizing effect of gastric emptying

l   Sugar content range between 5-20% (~6-24 Calories per ounce)

l   Contains fructose + electrolytes (Na, Cl, K, P)

l   Examples:

l  GatorLode & Ultra Fuel

How do we go about CHO supplementation for exercise? [Table 9.9]

l    Sport event or exercise < 60 minutes duration


How do we go about CHO supplementation for exercise? [Table 9.9]

l    Sport event or exercise 1-4 hours duration


How do we go about CHO supplementation for exercise? [Table 9.9]

l    Sport event or exercise > 4 hours duration


Selection of CHO for performance

l    Types of CHO

l    Fructose

l   Absorbed more slowly than glucose from intestine; hence, slower insulin response

l   Allows for more stable blood sugar during early stages of prolonged exercise if ingested 45 min prior to activity

l   If ingested immediately before or during exercise, its effect is no different than glucose

l   One drawback – can cause gastrointestinal distress during exercise and affect performance if taken as only CHO and in greater concentrations

Selection of CHO for performance

l   Types of CHO

l   Glucose Polymers

l  A chain of glucose molecules

l  Allows for rapid gastric emptying, digestibility, and absorption due to lesser osmotic effect (less concentrated)

l  Allows for rapid fluid and glucose replacement at rest and during exercise

l  Don’t show significant advantage over other CHO solutions during exercise

Selection of CHO for performance

l   Types of CHO

l   Solid and liquid CHO

l  When consumed prior to exercise, both forms are effective in maintaining blood glucose levels during performance

l  Liquid CHO may be fuel of preference for prolonged exercise

Selection of CHO for performance

l   Types of CHO

l   Low-glycemic-index foods

l  Since the CHO from these foods are taken up more slowly, one would suspect that these foods would give more available glucose in the latter stages of a prolonged event

l  Most research comparisons between low- and high-glycemic foods show no difference in performance benefit

Selection of CHO for performance

l   Key to CHO selection

l   Individuality

l  Each person should determine which forms of CHO work for them

l  Some individuals can tolerate higher glycemic- index foods compared to lower glycemic-index foods during competition

CHO replenishment following prolonged exercise

l   Athletes may be performing in several events in one day or train 2-3 times per day

l   Ingesting CHO during rest intervals has shown to be beneficial to events later in day

l  Blood glucose and muscle glycogen resynthesized

l  High glycemic-index foods are most effective (such as potatoes, bread, glucose, glucose drinks)

CHO replenishment Guideline

l   For prolonged exercise tasks with ~ 4 hour intervals between exercise bouts

l   Consume 1 gram of CHO per kg of body weight

l  Immediately after the 1st endurance event and also 2 hours before the 2nd endurance event

l  Additional CHO may be consumed immediately before and during the 2nd endurance event

Potential CHO + Other Nutrient Replenishment of Used Energy Fuel

l    Ingesting CHO with protein has shown a faster rate of glycogen resynthesis in 4 hours after intensive event compared to CHO or protein intakes alone

l    Ingesting CHO + protein + fat no different than CHO alone in restoring muscle glycogen after exercise

l    Ingesting CHO + creatine increased muscle glycogen stores above that provided by CHO alone


Commercial Products of CHO replenishment

l    High CHO + Protein products

l    GatorPro

l   59 grams of CHO + 17 grams of protein + 7 grams of fat in 11 oz can; 2 cans appear optimal

l    Total: 118 grams CHO, 34 grams protein, 14 grams fat

l    Power bars

l   40 grams of CHO + 10 grams of protein + 2 grams of fat in one bar; 3 bars appear optimal

l    Total: 120 grams CHO, 30 grams protein, 6 grams fat

l    Large bagel + 3 oz lean turkey breast + PowerAde (24 oz)

l   Total: 110 grams CHO, 33 grams protein

During intensive training for a sport

l   Daily recommendation for replenishment of muscle glycogen

l   8-10 grams of CHO per kg of body weight per day

l  Example:

l   For a 70 kg person, this approximates
l    560-700 grams CHO day or 2,240-2,800 Cals from CHO during the day

l   Ultraendurance athletes

l  Should take in 14 or more grams of CHO per kg of body wt per day


What form of CHO replenishment should be utilized after a prolonged event?

l   Within initial 24 hours after the event

l   Simple or complex CHO will be effective in replacing lost muscle glycogen stores

l  Inclusion of high glycemic-index foods will help speed recovery

l   Beyond 24 hours after the event

l   Complex CHO will be more effective than simple CHO in replacing lost muscle glycogen

How long will it take to recover lost muscle glycogen from prolonged event?

l   Usually 7 or more days

l   This is due to the muscle damage from the endurance event

l   Significant reduction in activity and rest are important during this time

How effective are consistent CHO diets on an athlete’s performance?

l    High CHO diets (75-85%)

l    Shown to enhance performance of endurance athletes and prolonged, moderately-intense intermittent activities (i.e. soccer game)

l    Moderate CHO diets (40-50%)

l    Shown not to impair prolonged performance

l    “Zone diet” (40% CHO:30% Fat:30% Protein)

l   May be sufficient to meet energy needs of training but has not been shown to improve performance

CHO Loading (Glycogen Super-compensation)

l    A dietary technique designed to promote a significant increase in glycogen content in both the liver and muscles in order to delay the onset of fatigue

l    Generally used during the 3-7 days prior to an endurance or prolonged “stop and go” competition (e.g. soccer, lacrosse)

l    Body builders use CHO loading to increase muscle glycogen levels so that they will gain the associated water retention

l    Fiber types affected

l    For endurance events, primarily ST and FTa

l    For prolonged, “stop & go”, primarily FTb

How do you CHO Load?

Does CHO loading increase muscle glycogen?

l    Yes

l    Similar response in males and females

l    Increase is 2-3 fold in muscle

l    2 fold in liver

l    Important to taper (allow less activity or rest before competition) at least 2 days prior to event

l    Training 45-60 min per day will lessen effect of CHO loading

l    Effect may last up to 3 days in rested athlete

How do we know if CHO loading worked?

l   One option

l   Muscle biopsy

l   Another option (not invasive)

l   Keep accurate record of body weight in mornings

l  Since we know that 3 grams of water bind to each gram of stored CHO, the following would be true

l   An additional 300-400 g of glycogen would bring 900-1,200 g of water with it; in this case, body weight would increase 1,200-1,600 g or 2.5-3.5 pounds


Who benefits from CHO loading?

l    It has not been found to enhance performance in single high-intensity exercise tasks of up to 60 min duration, in most cases

l    It has been shown to benefit athletes in prolonged intermittent high intensity events, e.g. ice hockey

l    It has been proven effective for prolonged aerobic events

l    It has been used by body builders to increase muscle size; not always effective

Can a shortened CHO loading time period be effective?

l    Yes

l    A 3-day CHO loading protocol (10 g of CHO per kg of body wt per day) can be effective in improving performance compared to a normal, mixed diet (6 g CHO per kg body wt)

l    It may increase performance in prolonged events by 2-3%

l    Most effective performance will occur with combination of CHO loading & CHO supplementation during the event

Are there detrimental effects of CHO loading?

l    Energy benefits generally outweigh the potential disadvantage of the extra weight gained

l    Individuals with diabetes should be cautious with its use due to the extra CHO load

l    Individuals with cholesterol problems should avoid use of the classic CHO loading scheme due to the use of the high-fat/high protein phase

CHO’s: Ergogenic or ergolytic?

l    Alcohol

l    Background information:

l   Beer – approx 4-5% alcohol

l   Wine – approx 12-14% alcohol

l   Liquor – approx 40-45% alcohol

l    Proof

l   Measure of alcohol content in a beverage; represents a doubling of alcohol content

l    E.g.  86 proof whisky has 43% alcohol

l    May be classified as a food since it provides energy

l   7 Calories per gram

l   Can only metabolize one-third per ounce (8-10 grams) of alcohol per hour (somewhat < amount of alcohol in 1 drink)

Alcohol Metabolism and Performance

l    Alcohol is derived from fermentation of CHO but it is metabolized like fat by the liver

l    Not been proven as a benefit to performance despite its conversion to fat

l    In small amounts, its has not been shown to affect performance, either + or –

l    In large amounts, it can hamper performance

l    Need significant amount of O2 to release Calories from alcohol


What about consuming a beer after a prolonged athletic event?

l   Drinks containing 4% alcohol or more tend to delay the recovery process

Will light social drinking affect performance event on the next day?

l   Does not appear to impair performance ability the following day after a light drink

l   Should abstain from drinking 24 hours prior to prolonged endurance event


Is it banned in sport competition?

l   Only in sports involving shooting competition

l   Originally, it was banned by IOC before 1972 for Olympic competition

l  Removed from banned list since it was consumed during many of the traditional European meals

Alcohol and Performance Summary

l   No data to support that it provides an ergogenic effect

l   In excess, it can become ergolytic to performance

CHO by-product “supplementation” and effects on performance

l    Fructose 1,6-diphosphate (FDP)

l    May prevent fast breakdown of muscle glycogen

l    No beneficial effect on performance

l    Pyruvate (6-19 g/day)

l    Shown to increase muscle mass and decrease body fat

l    No data available concerning its effect on performance

l    DHAP (combination of pyruvate + dihydroxyacetone)

l    Shown to increase glucose extraction by exercising muscle

l    Can increase endurance time of untrained individuals

CHO by-product effects on performance

l   Lactate salts

l   Thought to buffer blood acidity

l   No apparent performance benefit

l   Ribose

l   Component of RNA, as well as ATP

l   May provide rapid recovery from brief, intensive exercise bouts, i.e. like creatine?

l   More studies need to be conducted