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Body Composition and Nutrition for Sport CHAPTER 15 Overview • Body composition in sport – Assessment – Sport performance – Weight standards – Achieving optimal weight • Nutrition and sport – Classification of nutrients – Water and electrolyte balance – Dehydration and exercise performance – Athlete’s diet – Sport drinks Body Composition in Sport • Body composition: body’s chemical and molecular composition • General models of body composition – Chemical model – Anatomical model – Two-compartment model Figure 15.1 Body Composition in Sport: Assessment • Provides more information – Height and weight not enough to know fitness status – Percent body fat, performance • Body composition measured several ways – – – – – Densitometry/hydrostatic weighing DEXA Air plethysmography Skinfold Bioelectric impedance Body Composition in Sport: Assessment • Densitometry: measures body density – Hydrostatic (underwater) weighing – Muscle heavier than water, fat lighter than water – Most commonly used method • Limitations of hydrostatic weighing – Lung air volume confounding – Conversion of body density to percent fat – Fat-free density varies among people Figure 15.2 Body Composition in Sport: Assessment • DEXA – Dual-energy X-ray absorptiometry – Quantifies bone and soft-tissue composition – Precise and reliable but expensive and technical • Air plethysmography (Bod Pod) – Another densitometry technique – Air displacement (instead of water) – Easy for subject, difficult for operator, expensive Figure 15.3a Figure 15.3b Figure 15.4 Body Composition in Sport: Assessment • Skinfold – Most widely used field technique – Measures thickness at a minimum of three sites – Uses quadratic equations, reasonably accurate • Bioelectric impedance – – – – Electrodes on ankle, foot, wrist, hand Current passes from proximal to distal sites Fat-free mass good conductor, fat poor conductor Reasonably accurate, could be better Figure 15.5 Figure 15.6 Body Composition in Sport: Sport Performance • Fat-free mass (includes muscle) – Important variable for athletes to know – Good for power, strength, muscle endurance – But bad for aerobic endurance (more mass to carry) • Relative body fat (percent body fat) – Fat: dead weight but useful energy store – Less fat usually = better performance – Exceptions: sumo wrestler, swimmer, weight lifter Body Composition in Sport: Weight Standards • Guide for optimal body size and composition for a given sport • Can be misleading – Elite athletes define optimal performance – But do elite athletes define optimal body? – Not always the case Figure 15.7 Body Composition in Sport: Weight Standards • Inappropriate use of weight standards – Seriously abused by coaches, players – Misconception that small weight loss good, large weight loss better – Can lead to performance, eating disorders • Making weight: severe weight loss – Wrestling, boxing, etc. – Weight classes can force extreme weight loss – Compete in class too low injury, poor health Body Composition in Sport: Risks With Severe Weight Loss • Dehydration – Fasting, extreme caloric restriction water loss – 2 to 4% weight loss as water impaired performance – Risk of kidney, cardiovascular dysfunction, death • Chronic fatigue – Underweight fatigue performance, injury – Mimics overtraining and chronic fatigue syndromes – Underweight substrate depletion Body Composition in Sport: Risks With Severe Weight Loss • Eating disorders – Weight standards can disordered eating – Anorexia nervosa, bulimia nervosa – More prevalent with women in lean sports • Menstrual dysfunction – Delayed menarche, oligomenorrhea, or amenorrhea – Prevalent in low-body-weight sports – Due to caloric intake < caloric expenditure Body Composition in Sport: Risks With Severe Weight Loss • Bone mineral loss – Serious consequence of athletic amenorrhea – Anorexia fracture rate 7 times higher • Female athlete triad – Eating + menstrual + bone mineral disorders – Seen with women in lean-physique, low-bodyweight, or endurance sports – Skating, dance, gymnastics, running, swimming Body Composition in Sport: Weight Standards • Appropriate weight standards – – – – Inappropriate standard risks athlete health Body composition, not total body weight Optimal range of percent body fat Account for sex differences • Weight standards not always appropriate – Technical measurement errors – Not all athletes perform best at ideal composition Table 15.1 Body Composition in Sport: Achieving Optimal Weight • Avoid fasting and crash diets – Cause more water and muscle loss, less fat loss – Ketosis accelerates water loss • Optimal weight loss: fat mass, FFM – – – – Moderate caloric restriction + exercise Caloric deficit ~200 to 500 kcal/day Lose no more than 0.5 to 1 kg/week When near goal, slow weight loss further Nutrition and Sport • Recommended macronutrient balance – Carbohydrate: 55 to 60% of daily kilocalories – Fat: <35% (<10% saturated) – Protein: 10 to 15% • Optimal for both performance and health Nutrition and Sport: Classification of Nutrients • Recommended Daily Allowance (RDA) – Outdated—not bad, just insufficient – Estimated safe, adequate dietary intakes and minimum vitamin and mineral requirements • Daily Recommended Intake (DRI) – Current standard – Groups intakes by nutrient function, classification – Four reference values: EAR, RDA, UL, AI Nutrition and Sport: Classification of Nutrients • Carbohydrate (CHO) • Fat (lipid) • Protein • Vitamins • Minerals • Water Nutrition and Sport: Classification of Nutrients—CHO • Molecular composition – Monosaccharide, disaccharide, or polysaccharide – Monosaccharides: glucose, fructose, galactose • Functions in body – Energy source (sole source for nervous system) – Regulate fat and protein metabolism • Consumption and storage – Excess CHO stored as glycogen – Dietary CHO intake determines glycogen stores Nutrition and Sport: Classification of Nutrients—CHO • Determinants of glycogen replacement – CHO intake – Exercise type (eccentric glycogen synthesis) • Glycogen maintenance – Requires 5 to 13 g CHO/kg body weight per day – In athletes, hunger often insufficient drive for CHO consumption – Insufficient CHO intake heavy, tired feeling Figure 15.8 Figure 15.9 Nutrition and Sport: Classification of Nutrients—CHO • Glycemic index (GI) categorizes food based on glycemic (blood sugar) response • High GI (GI >70): sport drinks, jelly beans, baked/fried potatoes, cornflakes, pretzels • Moderate GI (GI 56-70): pastry, pita bread, white rice, bananas, soda, ice cream • Low GI (GI ≤55): spaghetti, legumes, milk, apples/pears, peanuts, M&M’s, yogurt Nutrition and Sport: Classification of Nutrients—CHO • GI not perfect – – – – Individual GI response varies Some complex CHOs have high GI Fat + high GI = lower GI GI calculations differ depending on reference food (glucose vs. white bread) • Glycemic load (GL) – Improved CHO index – GL = (GI x CHO, g)/100 Nutrition and Sport: Classification of Nutrients—CHO • CHO factors that exercise time – Normoglycemia, low-GI preexercise snack – CHO loading (1-3 days prior) – CHO feedings during exercise • CHO factors that exercise time – Hypoglycemia, high-GI preexercise snack – No CHO loading (lower glycogen stores) – No CHO feeding during exercise Figure 15.10 Figure 15.11 Nutrition and Sport: Classification of Nutrients—CHO • CHO during exercise – Unlike preexercise CHO, does not trigger hypoglycemia – Improved muscle permeability to glucose? – Insulin-binding sites altered during exercise? • CHO intake after exercise essential – Glycogen resynthesis high <2 h after exercise – Protein + CHO intake enhances glycogen stores – Stimulates muscle tissue repair Figure 15.12 Nutrition and Sport: Classification of Nutrients—Fat • Fat essential for body function – Fuel substrate (triglycerides FFAs + glycerol) – Component of cell membranes and nerve fibers – Required by steroid hormones and fat-soluble vitamins • Saturated versus unsaturated FFAs – Total fat <35% of total daily kilocalories (0 trans fat) – Saturated fat <10% total daily kilocalories – Cholesterol <300 mg/day Nutrition and Sport: Classification of Nutrients—Fat • FFAs important fuel during exercise – Delay exhaustion after glycogen depletion – Body cannot metabolize triglycerides (dietary fat) – Must break down triglycerides into FFAs • High-fat versus high-CHO diets – High-fat intake circulating FFAs (good) – High-fat intake glycogen storage (bad) – No conclusive evidence on high-fat diets Nutrition and Sport: Classification of Nutrients—Protein • Protein essential for body function – Cell structure, growth, repair, and maintenance – Used to produce enzymes, hormones, antibodies, and as buffer – Controls plasma volume via oncotic pressure • 20 amino acids: essential versus nonessential • Protein consumption – 15% of total daily kilocalories – ~0.80 g protein/kg body weight per day Table 15.2 Nutrition and Sport: Classification of Nutrients—Protein • Protein requirements higher for athletes – 1.2 to 1.7 g protein/kg body weight per day – Endurance training: may use as fuel substrate – Strength training: needed for building muscle • Excessive protein intake health risks • CHO + protein after exercise improved glycogen and muscle protein synthesis Nutrition and Sport: Classification of Nutrients—Vitamins • Small but essential organic molecules – Enable use of other ingested nutrients – Act as catalysts and cofactors in chemical reactions • Fat soluble versus water soluble – Fat soluble stored, can reach toxic accumulations – Water soluble excrete, toxicity difficult to reach • In general, unless vitamin deficiency exists, supplementation not helpful Nutrition and Sport: Classification of Nutrients—Vitamins • B-complex vitamins (12+ total) – Essential for cellular metabolism, ATP production – Needed for pyruvate acetyl-CoA, formation of FAD and NADP, erythropoiesis • Vitamin C – Important for collagen maintenance, antioxidant – Also, adrenal hormone synthesis, iron absorption • Vitamin E – Stored in muscle and fat – Potent antioxidant Nutrition and Sport: Classification of Nutrients—Antioxidants • Free radicals – Cellular by-product of oxidative phosphorylation – Highly reactive, may precipitate fatigue • Antioxidants – Quench free radicals, prevent oxidant damage – Muscle antioxidant enzymes – Dietary antioxidants: vitamins E and C, b-carotene Nutrition and Sport: Classification of Nutrients—Minerals • Minerals – Inorganic substances needed for cellular function – Macrominerals versus microminerals (trace elements) • Calcium – Bone density, nerve and muscle function – Concerns: osteopenia, osteoporosis • Phosphorus – Bound to calcium in bones – Important for metabolism, cell membranes, buffers, bioenergetics Nutrition and Sport: Classification of Nutrients—Minerals • Iron – Critical for hemoglobin, myoglobin (O2 transport) – Deficiency anemia – Excess iron toxicity • Sodium, potassium, chloride – Na+, Cl- found primarily in interstitial fluid – K+ in intracellular fluid – Needed for nerve impulses, cardiac rhythm, fluid and pH balance – Excess intake dangerous Nutrition and Sport: Classification of Nutrients—Water • 50 to 60% of total body weight – Fat-free mass 73% water versus fat mass 10% water – 1 to 6% body weight loss in sweat common for athletes – 9 to 12% loss can be fatal – 2/3 body water intracellular, 1/3 extracellular • Medium for transportation, diffusion • Regulates temperature • Maintains blood pressure Nutrition and Sport: Water and Electrolyte Balance • Water gain at rest (33 ml/kg/day) – 60% from beverages – 30% from food – 10% from cellular respiration • Water loss at rest – – – – Evaporation from skin, respiratory tract (30%) Excretion from kidneys (60%) Excretion from large intestine (5%) Sweat (5%) Nutrition and Sport: Water and Electrolyte Balance • Dehydration during exercise – Sweat due to higher body temperature – Water loss > water gain • Body temperature and sweating affected by – – – – – Environmental temperature, radiant heat load Humidity Air velocity Body size Metabolic rate Table 15.4 Figure 15.13 Nutrition and Sport: Dehydration and Exercise Performance • Impairs aerobic performance – Temperature sweat loss performance – Plasma volume cardiovascular function – Plasma volume thermoregulatory function • Effect of dehydration on anaerobic and strength performance unclear Figure 15.14 Nutrition and Sport: Dehydration and Exercise Performance • Electrolyte loss in sweat – Sweat similar to (and derived from) plasma – Mostly Na+, Cl- (concentrations will vary) – Remaining ions in body must redistribute • Electrolyte loss in urine – Kidneys regulate electrolyte excretion – Urine production = electrolyte excretion – Aldosterone Na+ retention thirst and drinking Table 15.5a Table 15.5b Table 15.6 Nutrition and Sport: Dehydration and Exercise Performance • Thirst – – – – Osmoreceptors (high blood osmolality) Baroreceptors (low blood volume) Thirst not well calibrated to hydration levels 24 to 48 h to completely rehydrate • Benefits of fluids during exercise – Minimize dehydration and water loss – Performance and cardiovascular function maintained Figure 15.15 Nutrition and Sport: Dehydration and Exercise Performance • Hyponatremia – Serum Na+ <135 mmol/L – Excessive Na+ loss + excessive rehydration – Relatively rare (e.g., ultramarathoners) • Symptoms – Mild: bloating/puffiness, nausea/vomiting, headache – More severe: cerebral edema, cognitive/central nervous system dysfunction, pulmonary edema, coma, death Nutrition and Sport: The Athlete’s Diet • Vegetarian diets – Vegan, lacto, lacto-ovo – Lacto-ovo fewer nutrition deficiencies – Need sufficient essential amino acids, total kilocalories, vitamin A, riboflavin, vitamin B12, vitamin D, Ca2+, zinc, iron • Precompetition meal – 200 to 500 kcal at least 2 h before competition – Mostly CHOs: cereal, milk, juice, toast – Liquid meals Nutrition and Sport: The Athlete’s Diet • Maximal glycogen stores performance • Carbohydrate (glycogen) loading – – – – Tapering training week before event Days 6 to 4 before event: normal CHO diet Days 3 to 1 before event: high CHO diet Muscle glycogen stores doubled Figure 15.16 Nutrition and Sport: The Athlete’s Diet • Diet prepares liver for endurance exercise – CHO loading greatly increases liver glycogen, reduces hypoglycemia – 1 g glycogen stored with 2.6 g water – CHO loading glycogen water weight gain • Back-to-back competition – Liver glycogen resynthesized quickly – Muscle glycogen resynthesized slowly – CHO + protein intake <2 h after competition Figure 15.17 Nutrition and Sport: Sport Drinks • Composition of sport drinks – Water + energy (CHO) + electrolytes – Widespread performance benefits • CHO concentration: energy delivery – CHO content slows gastric emptying – Most drinks have 6 to 8 g CHO per 100 ml fluid – Mostly glucose, glucose polymers Nutrition and Sport: Sport Drinks • Na+ concentration: aids rehydration – – – – Glucose and Na+ stimulate water absorption Na+ thirst and palatability Na+ retention promotes water retention 20 to 60 mmol/L • What works best? – Light flavor, no strong aftertaste – Taste, composition ad libitum consumption