Issues in Sports Nutrition

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. Untrained Trained 0% 50% 100% Blood Glucose Triglyceride Glycogen Plasma FFA Substrate Utilization During Exercise * • Carbohydrateloaded • Blood sugar maintained • Serum fatty acids low • Protein utilization low • % Of maximum workload maintained • Carbohydratedepleted • Blood sugar declines • Serum fatty acids rise • Protein utilization increases • % 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% Rest LightHighHighModerate intensity intensity Sprint Endurance Protein Glycogen Fat 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 • • • • • • 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 • • • • • • • • 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 Steen. Aspen Publ. 1998 by WD McArdle, FI Katch, VL Katch. Lippincott, Williams, & Wilkins, 1999 by JR Berning, SN • Nutrition for Sport & Exercise • Clinics in Sports Medicine WB Saunders 1999