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
ą/ł 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