Sports Nutrition

Darwin Deen, MD, MSAlbert Einstein College of Medicine

Sept. 2000

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

Time to Exhaustion, min.

050

100150200

LowCHO

NormalDiet

HighCHO

Minutes

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.

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