Transcript Sports Nutrition - وبسایت تخصصی تربیت بدنی

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Sports Nutrition
Darwin Deen, MD, MS
Albert Einstein College of Medicine
Sept. 2000
Issues in Sports Nutrition
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Exercise physiology and nutrition
Carbohydrates as fuel
Protein requirements
Fats and exercise
Vitamins and Minerals
Fluid needs
Ergonomic aids
Eating disorders
School-age athletes
Substrates Used/produced During Exercise
• Strenuous
exercise
• Anaerobic:
• Glucose is cleaved
into 2 molecules of
pyvruate
• Pyruvate is
converted to lactate
• Lactate is recycled
by the liver
• Light/moderate
exercise
• Aerobic:
• Pyruvate is broken
down to carbon
dioxide and water
• Requires oxidative
phosphorylation in
the mitochondria
Substrate Utilization During Exercise
• Given adequate stores, carbohydrate is
the preferred fuel.
• Triglycerides provide between 30 and
80% of the energy for physical activity.
• How much fat is used is determined by
the person’s nutritional and fitness
status and the intensity and duration of
exercise.
Substrate Utilization During Exercise
• During the first minute of maximal
exercise, most energy is generated
anaerobically.
• By the second minute, 50% of energy is
from aerobic metabolism.
• By 30 minutes, 95% is aerobic.
• Over the time course of a marathon,
only 20% of the energy comes from
triglycerides.
Substrate Utilization During Exercise
• With
training,
fat
utilization
becomes
more
efficient.
Untrained
Trained
0%
Blood Glucose
Triglyceride
50%
100%
Glycogen
Plasma FFA
Substrate Utilization During Exercise *
• Carbohydrate-loaded • Carbohydrate• Blood sugar
depleted
maintained
• Blood sugar declines
• Serum fatty acids
• Serum fatty acids
low
rise
• Protein utilization
• Protein utilization
low
increases
• % Of maximum
workload maintained • % Of maximum
workload declines
• *Within 20-40 min
Time to Exhaustion, min.
Minutes
200
150
100
50
0
Low Normal High
CHO
Diet CHO
Substrates Used During Exercise
100%
90%
80%
70%
60%
50%
40%
30%
20%
10%
0%
Protein
Glycogen
Fat
Rest
LightHighHighModerate intensity intensity
Sprint Endurance
Protein Requirements for Exercise
• Inadequate
protein intake will
lead to muscle
breakdown
• Excess protein
intake will be
used for energy
• Protein
requirements vary
for different
activities
1.7
Strength
Endurance
Vegetarian
Sedentary
1.2
0.9
0.8
0
1
g/kg
2
Diet Periodization
• Alternating periods of carbohydrate
restriction with carbohydrate loading
• Little good data
• Probably not harmful thought also
probably not helpful
• Avoid long-term complications of highfat diets
Vitamin and Mineral Intake in Athletes
• Anti-oxidant
vitamins
– Vitamin C
– Vitamin E
• B vitamins
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Calcium
Magnesium
Phosphate
Iron
Zinc
Chromium
Evidence-based supplementation
• Deficiencies hinder performance.
• Studies document that athletes only
suffer deficiencies if they follow
restrictive diets.
• Supplements given to non-deficient
athletes do not improve performance.
• Most blood levels of vitamins do not
change much with supplementation.
Anti-oxidant vitamins
• Vitamin C
– Supplements have
been shown to
reduce lipid peroxide
formation during
strenuous exercise.
– Vit C has been
unsuccessful in
preventing the
relative
immunosupression
caused by endurance
exercise.
• Vitamin E
– Supplements of 200
IU daily have been
recommended to
prevent endurance
exercise induced lipid
peroxidation.
– Vitamin E is
redistributed to
muscles after
exercise.
– Supplement don’t
have much effect.
B vitamins
• In a study comparing 55 athletes with
20 sedentary controls, the athletes had
higher dietary intakes but lower serum
levels of B1, B6, and E.
• Reduced levels of pyridoxal 5phosphate were found in both groups
but supplementation only improved this
level in the sedentary group.
Iron
• Prevalence of low ferritin levels is greater in
female athletes than non-athletes
• Supplements are indicated when low ferritin
levels are documented
• In addition to inadequate intake, athletes
may lose iron via sweat and GI bleeding
• No effect on performance has been found in
non-anemic subjects
Calcium
• Both calcium intake and physical activity
determine peak bone mass
• Many females fail to consume adequate
calcium (1200 mg/d)
• Calcium supplement should be consumed
between meals (except caco3)
• Calcium supplements may interfere with nonheme iron absorption (except citrate)
Chromium
• Chromium was dubbed “the nutrient of
the 90s” by the supplement industry.
• A few small studies indicated more
rapid gain of LBM in female athletes
with Cr supplements.
• Cr Picolinate assists insulin binding to
its receptor.
• A role for Cr in weight loss or sports has
not been established.
Fluid Needs of Athletes
• Exercise doubles daily fluid loss in warm
weather (3300 to 6600 ml)
• ACSM guidelines recommend consumption of
16 oz of fluids within 2 hours of exercise
• Hydration fluids are absorbed more rapidly if
they contain some sodium chloride
• Hydration promotes cooling and improves
performance
Proposed Ergonomic Aids
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Creatine
Caffeine
Beta-hydroxy beta-methylbuterate
DHEA
Boron
Branched chain amino acids
Choline
Amino Acid Supplements
Creatine
• Creatine-phosphate supplies energy to
ATP in muscle
• Supplementing with 20-30 g/d of
creatine for 4-6 days can increase
muscle concentrations for weeks
• Has been shown to enhance
performance of repeated bouts of highintensity exercise
Eating Disorders in Athletes
• Pressure to be competitive leads to
disorders eating.
• Female gymnasts & male wrestlers are
particularly at risk.
• Athletes try to hide this problem and
will rarely ask for help.
• Eating disorders impact performance.
Considerations for the School-aged Athlete
• The nutrient needs for growth and sport
must both be considered.
• Adequate body fat for pubertal
development is important.
• Monitor growth and maturation
• Ensure adequate hydration.
• Be alert for inappropriate attempts to
control body weight.
“Bulking-up”
• If a physician determines that an athlete has the
potential to increase lean body mass, the following
components are necessary for success:
– An appropriate progressive resistance-training
program.
– Adequate rest and sleep.
– Adequate energy intake (an additional 750900kcal/d).
– Five to nine eating occasions a day.
– Increased amount of food if possible.
– High energy supplements.
– Adequate protein intake.
References
• Sports & Exercise Nutrition
by WD McArdle, FI
Katch, VL Katch. Lippincott, Williams, & Wilkins, 1999
• Nutrition for Sport & Exercise
by JR Berning, SN
Steen. Aspen Publ. 1998
• Clinics in Sports Medicine WB Saunders 1999
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