Chapter 15

Body Composition and Nutrition for

Sport

CHAPTER 15 CHAPTER 15 OverviewOverview

• 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 SportBody Composition in Sport

• Body composition: body’s chemical and molecular composition

• General models of body composition– Chemical model– Anatomical model– Two-compartment model

Figure 15.1Figure 15.1

Body Composition in Sport:Body Composition in Sport:AssessmentAssessment

• 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


• 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


• 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 15.3Figure 15.3aa

Figure 15.3Figure 15.3bb


• 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

Body Composition in Sport:Body Composition in Sport:Sport PerformanceSport 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:Body Composition in Sport:Weight StandardsWeight 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


• 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:Body Composition in Sport:Risks With Severe Weight LossRisks 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:Body Composition in Sport: Risks With Severe Weight Loss 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:Body Composition in Sport: Risks With Severe Weight Loss 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-body-

weight, or endurance sports– Skating, dance, gymnastics, running, swimming


• 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 15.1Table 15.1

Body Composition in Sport:Body Composition in Sport:Achieving Optimal WeightAchieving 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 SportNutrition 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:Nutrition and Sport:Classification of NutrientsClassification 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:Nutrition and Sport:Classification of NutrientsClassification of Nutrients

• Carbohydrate (CHO)

• Fat (lipid)

• Protein

• Vitamins

• Minerals

• Water

Nutrition and Sport:Nutrition and Sport:Classification of Nutrients—CHOClassification 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:Nutrition and Sport:Classification of Nutrients—CHOClassification 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

Nutrition and Sport:Nutrition and Sport:Classification of Nutrients—CHO 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


• 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


• 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


• 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

Nutrition and Sport:Nutrition and Sport:Classification of Nutrients—Fat 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:Nutrition and Sport:Classification of Nutrients—Fat 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:Nutrition and Sport:Classification of Nutrients—ProteinClassification 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

Nutrition and Sport:Nutrition and Sport:Classification of Nutrients—Protein 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:Nutrition and Sport:Classification of Nutrients—Vitamins 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:Nutrition and Sport:Classification of Nutrients—Vitamins 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 Nutrition and Sport: Classification of Nutrients—Antioxidantsof 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, -carotene

Nutrition and Sport:Nutrition and Sport:Classification of Nutrients—Minerals 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:Nutrition and Sport:Classification of Nutrients—Minerals 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:Nutrition and Sport:Classification of Nutrients—Water 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:Nutrition and Sport:Water and Electrolyte BalanceWater 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:Nutrition and Sport:Water and Electrolyte BalanceWater 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

Nutrition and Sport: Dehydration Nutrition and Sport: Dehydration and Exercise Performanceand 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


• 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 15.5Table 15.5aa

Table 15.5Table 15.5bb


• 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

Nutrition and Sport: Dehydration and Nutrition and Sport: Dehydration and Exercise PerformanceExercise 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:Nutrition and Sport:The Athlete’s DietThe 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


• 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


• 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

Nutrition and Sport:Nutrition and Sport:Sport DrinksSport 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:Nutrition and Sport:Sport DrinksSport 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

Chapter 15

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