Post on 13-Dec-2015
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Issues in Sports Nutrition
• 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.
0% 50% 100%
Trained
Untrained
Blood Glucose GlycogenTriglyceride Plasma FFA
Substrate Utilization During Exercise *
• Carbohydrate-loaded
• Blood sugar maintained
• Serum fatty acids low
• Protein utilization low
• % Of maximum workload maintained
• Carbohydrate-depleted
• Blood sugar declines
• Serum fatty acids rise
• Protein utilization increases
• % Of maximum workload declines
• *Within 20-40 min
Substrates Used During Exercise
0%10%20%30%40%50%60%70%80%90%
100%
Rest Light-Moderate
High-intensitySprint
High-intensity
Endurance
ProteinGlycogenFat
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
0.8
0.9
1.2
1.7
0 1 2g/kg
Strength
Endurance
Vegetarian
Sedentary
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
high-fat diets
Vitamin and Mineral Intake in Athletes
• Anti-oxidant vitamins– Vitamin C– Vitamin E
• B vitamins
• 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 5-phosphate 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 non-heme 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
• 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 high-intensity 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 750-
900kcal/d). – Five to nine eating occasions a day.– Increased amount of food if possible. – High energy supplements. – Adequate protein intake.