Sports Nutrition Darwin Deen, MD, MS Albert 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.

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 min

Time to Exhaustion, min.

Substrates Used During Exercise

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

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 B 1, B 6, 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 caco 3 ) 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 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 kcal/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 Clinics in Sports Medicine WB Saunders 1999