Transcript Basic Human Nutrition Lecture 8

Basic Human Nutrition
Lecture 8
Sports Nutrition
Benefits of physical activity
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Assists with weight maintenance
Increases lean body mass
Improves cardiovascular performance
Improves resistance to disease,
specifically heart disease, diabetes, high
blood pressure, stroke and some
cancers
Benefits of physical activity
continued
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Improves mental outlook
Improves flexibility and strength
How do you get physically fit?
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Four components of fitness:
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Flexibility
Muscle strength
Muscle endurance
Cardio-respiratory endurance
To build fitness, a person must engage in
physical activity. Muscles adapt to activities
they are called upon to perform.
Physical Activity Guidelines
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Frequency of activity – 3 -5 days per week
Intensity of activity: 55 to 90% of maximum
heart rate
Duration of activity: 20 to 60 minutes of
continuous activity
Physical Activity Guidelines
continued
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Mode of activity – any activity that
uses large muscle groups
Resistance activity: strength training of
moderate intensity at least 2 times per
week
Flexibility activity: stretching major
muscle groups 2 -3 times per week.
Muscles adapt to activity
demands
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In response to an overload of physical
activity, muscle cells gain strength and size
called hypertrophy. If not used, muscles
atrophy.
Periodic rest is necessary for muscles to
adapt. During rest, muscles build more of the
equipment they need to perform the activity.
Benefits of weight training
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Weight training builds lean body mass
Develops strength and endurance of
muscles and benefits health and overall
fitness.
Weight training helps maximize and
maintain bone mass
Cardiorespiratory endurance
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Increases cardiac output and oxygen
delivery
Increases heart strength and stroke
volume
Slows resting pulse
Increases breathing efficiency
Improves circulation
Reduces blood pressure
Fuels that support physical
activity are:
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Glucose from carbohydrate
Fatty acids from fat
Small amounts of amino acids from
protein.
The body uses different mixtures of
fuels at different times depending on
the intensity and duration of the activity
and the body’s own prior training
Body’s use of fuels continued
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During rest, half of the body’s energy comes
from fatty acids, rest from glucose and a little
from amino acids.
During physical activity, muscle glycogen is
the major fuel in the first few minutes.
As the activity continues, hormone
epinephrine, signals the liver and fat cells to
liberate glucose and fatty acids. The muscles
pick up the nutrients from the blood.
Glucose use and storage
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Body’s glycogen stores in the liver and
muscles are limited.
Intense activities, like sprinting use
glycogen quickly. Glycogen depletion
occurs after about 2 hours of intense
activity.
A high-carbohydrate diet enhances an
athlete’s endurance by ensuring
adequate glycogen stores.
Aerobic use of glycogen
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During moderate activity, the lungs
and circulatory system can keep up with
the muscles’ need for oxygen.
The person breathes easily, heart rate
is elevated but at a steady pace.
Activity is aerobic.
Aerobic use of glycogen
continued
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In aerobic activity, muscles extract their
energy from both glucose and fatty
acids when both are present together
with oxygen.
A little glucose helps metabolize a lot of
fat.
Moderate Aerobic activity conserves
glycogen stores.
Anaerobic Use of Glucose
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During intense activity, the heart and
lungs can only provide so much oxygen
so fast.
The demand for energy outstrips the
oxygen supply
Aerobic metabolism cannot meet the
energy needs.
Anaerobic use of glycogen
continued
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Muscles rely more heavily on glucose
which can be partially broken down by
anaerobic metabolism.
Muscles draw more heavily on their
limited glycogen supply.
Lactic Acid
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Anaerobic breakdown of glucose produces
lactic acid
Lactic acids are fragments of glucose
molecules that accumulate in the tissues and
blood.
Nervous system and hormones detect these
fragments and speed up heart and lungs to
draw in more oxygen to breakdown the
fragments.
Activity Duration and Glucose
Use
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For first 10 minutes – muscles rely on
glycogen.
Muscles use up about 1/5 of available
glycogen in about 20 minutes of
moderate activity.
Body responds by increasing uptake of
blood glucose.
Activity duration and glucose
use continued
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In moderate exercise that continues past 20
minutes, the body begins to use fat for fuel,
but glucose use still continues.
If activity continues, glycogen stores run out.
When glycogen stores are depleted, physical
activity can continue for a short time only
because the liver makes more glucose from
lactic acid and certain amino acids.
Activity Duration and Glucose
Use continued
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With glycogen stores depleted, exhaustion
and hypoglycaemia results and all activity
ceases.
To postpone exhaustion, endurance athletes
must maintain their glucose concentrations
for as long as they can.
Maintaining blood glucose for
activity
4 diet strategies:
1)
Eat a high CHO diet on a daily basis
2)
Take glucose during activity
3)
Eat CHO-rich foods after the activity to
boost the storage of glycogen
4)
CHO loading. Training muscles to
maximize glycogen stores
Carbohydrate loading
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Is manipulation of activity and CHO
intake to trick the muscles into storing
extra glycogen before competitive
sports
1 week before competition:
first 4 days, athlete trains moderately
hard (1-2 hrs/day) and eats a diet
moderately high in CHO.
Carbohydrate loading
continued
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Last 3 days of week, athlete cuts back
on activity and eats a very high CHO
diet (8 g CHO per kg body weight or
70% of calories)
With CHO loading, athletes can store
extra glycogen to fuel activity up to 90
minutes or longer.
Carbohydrate loading
continued
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In hot climate, extra glycogen beneficial as
glycogen releases water when broken down.
Eating a high-CHO meal within 2 hours after
physical activity accelerates glycogen storage
by 300%.
Timing is important. Eating the high CHO
meal after the 2 hours has passed, decreases
the rate of synthesis of glycogen by almost
half.
Training effect on glycogen
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Trained muscles versus untrained
muscles:
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adapt to store more glycogen
burn more fat at higher intensities
therefore, require less glucose to perform
the same amount of work
Training effect on glycogen
continued
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A trained person uses less glycogen per
minute to support an activity than an
untrained person
A trained person can work at higher
intensity for longer periods than an
untrained person while using the same
amount of glycogen
Should athletes eat more fat?
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An athlete who eats a fat-rich diet with
little CHO will burn more fat during
activity, but will sacrifice endurance.
A high-fat diet requires more oxygen to
yield energy, therefore more stress is
placed on the heart to supply the
oxygen to the muscles
Should athletes eat more fat
continued…
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High-fat diets increase risks of
cardiovascular disease
Body fat stores are a more important
source of energy for the athlete than fat
in food.
Body fat as fuel
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Fat stores are (theoretically) an unlimited
source of fuel.
Early in activity, muscles draw on fat from 2
sources- fats stored within working muscles
and fats from fat deposits under the skin.
Areas that have the most fat to spare donate
the greatest amounts of fatty acids to the
blood.
Intensity affects fat use
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Intensity of activity affects percentage
of energy used from fat.
Fat can only be broken down for use
aerobically.
When intensity surpasses body’s ability
to supply energy aerobically, the body
cannot burn more fat. It burns more
glucose.
Duration of activity affects fat
use…
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At start of activity, blood concentration
of fatty acids fall
Norepinephrine signals fat cells to break
stored triglycerides apart to release
fatty acids into the blood.
After 20 minutes, blood concentration
of fatty acids rises above normal resting
concentration.
Affect of duration of activity
on fat use continued
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Only during this phase of sustained,
moderate activity after the first 20
minutes, do the fat cells shrink and
empty out their stored fat.
Training-repeated aerobic activity,
stimulates the muscles to develop more
fat-burning enzymes.
Fat as energy continued
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Trained muscles burn fat more readily.
Heart and lungs become better at
supplying oxygen during high intensities
and enables muscle to burn more fat.
Protein builds muscle
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Athletes use protein to build and
maintain muscle and other lean
structures.
After physical activity, muscles increase
rate of protein synthesis – they build
more muscle to perform the activity.
To rebuild itself, muscle must first be
broken down then rebuilt.
Protein for muscle building
continued…
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Physical activity with a slight overload
results in larger muscles.
Dietary protein supplies the amino acids
to build protein
Genetic code in nuclei of muscles know
when protein is needed and which type
of protein to support each type of
activity.
Protein continued
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Intensity and pattern of muscle contractions
initiate signals for the muscles cells to
develop specific proteins
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E.g., weight lifter – more muscle fibers for bulk
and strength and more enzymes for making and
storing glycogen.
A jogger’s cells respond by producing proteins for
aerobic oxidation of fat and glucose.
Protein used for fuel
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A weight lifter may add between ¼ oz
and 1 oz (7 and 28g) of protein each
day to muscle mass. This protein comes
from dietary protein.
Athletes retain more protein and use a
little more as fuel than untrained
people.
Protein use for fuel continued
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The body speeds up its use of amino
acids for energy during physical activity.
Protein contributes about 10% to total
energy.
Factors that regulate protein use:
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Carbohydrate intake
Intensity and duration of activity
Degree of training
How much protein is needed?
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Athletes require only a small amount
more than untrained people.
Joint paper by American Dietetic
Association and Dietitians of Canada
recommends:
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1.0 to 1.5g per kg of body weight per day.
Vitamins and Minerals
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B vitamins – Thiamine, riboflavin and niacin
are important to energy release from
nutrients.
Vitamin B6 and B12 play key roles in the
release of energy, liberation of glucose from
glycogen and formation of haemoglobin.
No evidence to support increases in any of
the above vitamins will enhance performance.
Vitamins and Minerals
continued
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Vitamins C and E- potent antioxidants.
High intensity activity increases oxygen
consumption tenfold which enhances
production of damaging free radicals in
the body.
Vitamin C protects Vitamin E from
oxidation which protects cell
membranes against oxidation.
Vitamins C and E continued
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Evidence indicates supplements with
Vitamins C and E or E alone might
benefit performance.
No recommended level as yet, still
under investigation.
Minerals continued
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Endurance athletes, especially women
at high risk for iron deficiency.
Physical activity impairs iron status:
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Iron excreted in sweat
Iron lost through red blood cell destruction
from high impact sports
Physical activity impairs iron
status continued
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Irion lost in some athletes through small
blood losses in digestive tract.
High iron demands of muscles for aerobic
metabolism
Habitually low iron intakes, vegetarianism
Sports anaemia
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Early in training, athletes can develop low
blood haemoglobin called sports anaemia.
This is a normal adaptation to physical
activity
Aerobic training promotes increases in fluid in
blood which dilutes concentration of red
blood cells in a unit of blood.
Sports anaemia goes away by itself even with
continued training. True anaemia does not.
Calcium
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Calcium intakes of females athletes are often
low due to calorie restriction, particularly in
dancers and gymnasts where weight is
important.
Female athletes at risk for osteoporosis and
increased risk for stress fractures.
Though activity generally builds bone mass,
extremes of activity may be detrimental to
bone health.
Chromium, zinc, copper,
magnesium
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Chromium, zinc and copper have specific
roles in physical activity
The excretion of all 3 increases during
physical activity, but not enough is known
about effect this has.
Magnesium deficiency affects muscle gains in
a given amount of training.
Losses in sweat are the same for trained and
untrained individuals.
Sodium and potassium
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Untrained people lose more
electrolytes: sodium, potassium and
chloride than trained people.
With regular physical activity, body
adapts and conserves these minerals.
Profuse sweating can deplete body of
potassium, but it is easily replaced with
a few fruits and vegetables.
Fluids and body temperature
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Need for water exceeds all other nutrients.
Physical activity accelerates water loss
through sweat and breathing (water exhaled
as vapor).
A loss of even 1-2% of body weight can
reduce a person’s capacity to do work.
A loss of 7% of body weight can lead to
collapse.
Temperature regulation
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Heat stroke – dangerous accumulation
of body heat with accompanying fluid
loss.
Athletes need to drink enough fluid
before, during and after an event to
prevent dehydration and heat stroke.
Temperature regulation
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Hypotehermia –significant loss of
body heat. Even in cold weather, sweat
losses occur.
Athletes need to drink warm or
beverages at room temperature to
prevent heat loss and dehydration when
engaging in cold weather activities like
cross-country skiing.
Fluid needs of athletes
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Endurance athlete can lose 2L or more
of water in every hour of activity.
Digestive system can only absorb about
1L per hour.
Athletes need to drink more in
preparation for competition. Extra water
is not retained in the body, but ensures
maximum hydration at time of event.
Water versus Sports Drinks
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Plain cool water is sufficient for most athletes
as water:
1) rapidly leaves the digestive tract and
enters tissues and
2) water cools the body from the inside out.
Endurance athletes are exception. Need
water and carbohydrate to replenish glucose
stores.
Sports drinks - benefits
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Taste good , so people drink more
Provide psychological benefits and some
essential nutrients for endurance athletes.
Provide fluid to prevent dehydration
Provide glucose in right proportion – about
7%. CHO concentration greater than 10%
delays gastric emptying and delivery of water
to tissues.
Sports drinks continued
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Contain sodium and other electrolytes
to help replace those lost in sweat.
Sodium helps to accelerate rate of fluid
absorption from the digestive tract.
Athletes can replace lost electrolytes
from activity with a meal following the
activity.
Sports drinks continued
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In strenuous activity in hot, humid
conditions, heavy sweating coupled
with plain water can dangerously dilute
sodium in the blood.
In this instance, electrolytes need to be
replaced during the activity—sports
drinks can do this.
Other beverages- Caffeine
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Caffeine in beverages in moderate
amounts (2 cups) can enhance athletic
performance.
Caffeine may stimulate release of fatty
acids early into blood thereby
conserving glycogen.
Caffeine
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Also a diuretic, can cause headaches,
stomach upset, diarrhea, constricts
blood vessels and raises blood pressure
all of which negatively impacts
performance.
Caffeine in national/international sports
restricted to <800 mg (5-6cups strong
coffee) 2 hours before an event.
Beverages continued
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Carbonated beverages – not a good idea.
Carbonation bubbles take up room in the
stomach, so drink less.
Alcohol – dehydrates and promotes excretion
of vitamins such as thiamin, riboflavin, folate,
calcium, magnesium and potassium.
Alcohol alters perception, reduces strength,
slows reaction and impairs judgement.
Choosing a performance diet
Key concepts:
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Nutrient density – foods with maximum
nutrients, vitamins, minerals for the
energy that they provide. E.g. meat
sandwich versus bowl of salad.
Choosing a performance diet
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Balance – Athletes need to eat for
energy as energy needs are immense3000 to 5000 calories per day. But,
must still chose foods from all 4 food
groups to prevent disease.
Diet should be based on Canada’s Food
Guide To Healthy Eating
Pre-Game meal
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Food should be CHO-rich and the meal light
(300 – 500 calories)
Meal should be easy to digest and should
contain fluids. E.g., bread, pasta, potatoes
and fruit juice.
Avoid high protein, high fat, high fibre foods
before a game –take too long to digest and
may cause stomach upset during game.
Pre-Game meal continued
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Meal should be completed 3-4 hours
before competition to allow stomach to
empty.
Special food bars do not provide all
nutrients, offer no advantage over food
and are expensive.
Male athletes and weight
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Some sports such as wrestling and horse
jockeys need to “make weight”. This can lead
to unhealthy practices of fasting, dehydration
through sweat in steam rooms and diuretics
to shed water before an event.
These practices are dangerous and diminish
performance during and for days after an
event.
Female athlete triad
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Disordered eating: coaches and athletes
have unrealistic expectations for weight
for performance.
Coaches may not understand that an
athlete’s body is denser: more muscle
and bone mass than non athlete,
therefore cannot use general population
standards for weight
Female athlete triad continued
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Amenorrhea: loss of menstrual cycles.
In normal population, may occur in
about 2% of pre-menopausal women,
but in female athletes, prevalence as
high as 66%.
Amenorrhea is not a normal adaptation
to physical activity – symptom of
something wrong.
Female athlete triad continued
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Amenorrhea characterized by low blood
estrogen levels, infertility and bone
mineral losses.
May be due to very low body fat.
May be due to vigorous training
combined with low food energy which
can result in low estrogen.
Female athlete triad continued
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Osteoporosis - Low estrogen contributes to
stress fractures and osteoporosis in later life.
Women with anorexia nervosa particularly at
risk.
Women with bulimia rarely cease
menstruating so may be spared bone loss.