9/17/2009. HPER 3970 Dr. Ayers. (courtesy of Dr. Cheatham)

Transcription

1 REVIEW: General Principles II What is the RDA? Level of intake for essential nutrients determined on the basis of scientific knowledge to be adequate to meet the known nutrient needs of practically all (97%) healthy persons. Energy Chapter 3 HPER 3970 Dr. Ayers (courtesy of Dr. Cheatham) 1

2 What is Energy? Many different forms: Light, chemical, mechanical In physiology: Energy represents the capacity to do work (mechanical energy) work = force x distance (W=F x d) power = work / time (P=W/t) Energy Expenditure (EE): Energy expended in kilojoules (kj) or kilocalories (kcal) per unit of time to produce power During the conversion from one type of energy to another, no energy is ever lost chemical energy mechanical energy + heat Humans are not very efficient: During cycling energy, only 20% of the chemical energy is converted to power The rest is converted to heat Helps to maintain body temperature but can also result in increased internal body temperature 2

3 Units of energy: Often expressed as calories or Joules 1 calorie = the energy needed to raise the temperature of 1 gram (1 ml) of water 1 C (1.8 F) Example: Food containing 200 kcal has enough energy to raise the temperature of 200 L of water 1 C Joule (SI Unit of energy) 1 J moves a mass of 1 gram at a velocity of 1m/sec Conversions: 1 calorie = J 1 kcal = kj 1 kcal = 1000 calories Energetic Efficiency Efficiency (effective work performed after muscle contraction) is expressed as the percentage of total work Humans are 20% efficient Calculating Efficiency Gross Efficiency (GE) GE(%) = (work accomplished/energy expended)x100 Economy: Oxygen uptake required to exercise at a certain intensity walk vs. run example 3

4 Measuring the Energy Content of Food Direct calorimetry is used to measure the energy content of food The food is combusted (oxidized) and the resulting heat is used as the measure of the energy content Usually, 1 gram of food is placed in a bomb calorimeter with high oxygen pressure The resulting heat is the calorie content of the food 4

5 Carbohydrate (CHO) Varies depending on the type of CHO 1 gram of glucose = 3.7 kcal 1 gram of glycogen = 4.2 kcal Generally: 1 gram of CHO = 4 kcal Fat (Lipids) Also depends on the structure / type of fat Generally: 1 gram of Fat = 9 kcal Protein (PRO) Depends on the type of PRO and nitrogen content Generally: 1 gram of PRO = 4 kcal Water (H 2 O): 0 kcal Not all the energy from foods is actually available to humans Incomplete absorption and digestion Fiber content of food Atwater Factors correct for these factors Coefficient of digestibility %% energy in a nutrient available to body 5

6 Coefficients of Digestibility: REVIEW: Write in your notes: One thing you learned today Explain this new information to a friend 6

7 REVIEW: Energy I What are the energy values (kcal/g) for: CHO Fat PRO H 2 0 Measuring Energy Expenditure Methods to measure EE in humans can range from direct (complex) to more indirect (simple) Examples: Direct Calorimetry Indirect Calorimetry Closed circuit spirometry Open circuit spirometry Doubly labeled water Heart rate monitoring 7

8 Direct Calorimetry Measures heat produced during activity Indirect Calorimetry All biochemical reactions ultimately depend on the oxygen supply I.C. refers to the amount of O 2 consumption and CO 2 production, not the measurement of heat Measurement of the Respiratory Exchange Ratio (RER) RER = VCO 2 / VO 2 1 L of O 2 = 482kcal 4.82 Can range from ~ 4.7 kcal to 5.0 kcal depending on the proportion of energy coming from the breakdown of fat and CHO 8

9 Closed & Open circuit Spirometry Methods to measure oxygen consumption and carbon dioxide production Closed circuit and open circuit spirometry (cont d) Breath By Breath Systems 9

10 Indirect Calorimetry and Substrate Utilization Gas exchange measurements allow an estimation of energy expenditure plus the substrate mixture used The substrate used for energy therefore determines the total amount of O 2 required and CO 2 produced Respiratory Quotient (RQ) RQ = VCO 2 / VO 2 Requires steady state state measurements In theory, RQ can range from 0.7 to = 100% fat; 1.0 = 100% CHO Measuring Energy Expenditure CHO C 6 H 12 O 6 + O 2 = CO 2 + H 2 O C 6 H 12 O 6 + 6O 2 = 6CO 2 + 6H 2 O RQ = 6CO 2 / 6O 2 = 1 Fat C 16 H 32 O 2 + O 2 = CO 2 + H 2 O C 16 H 32 O O 2 = 16CO H 2 O RQ = 16CO 2 / 23O 2 = (0.7) Limitations of using RQ Steady state conditions required CO 2 produced must be entirely from the substrate oxidation H + + HCO 3 H 2 CO 3 H 2 O + CO 2 This buffering of H from lactic acid produces CO 2, ergo violates RQ 10

11 Components of Energy Expenditure Energy is needed for different processes in the body: Basal functions Digestion Absorption Metabolism Storage of food Energy for exercise / physical activity Resting Metabolic Rate (RMR) Theenergyrequired energy required for the maintenance of normal body functions and homeostasis in resting conditions Influenced by SNS activity, thyroid hormones, Na K pumps 60 to 75% of daily EE in a relatively inactive person Basal Metabolic Rate (BMR) The lowest oxygen uptake in resting thermoneutral conditions. Strict testing conditions Rarely used anymore 11

12 Diet Induced Thermogenesis (DIT) A.K.A.Thermic Effect of Food (TEF) Increase in EE above RMR that occurs for several hours after the ingestion of a meal Result of digestion, absorption, metabolizing, and storage of food ~10% of the daily EE Factors influencing i magnitude of DIT/TEF: Energy intake of food, size of meal, composition of meal, metabolic fate of meal Storing Fat = ~3% of the energy of the ingested meal Storing CHO = ~7% Synthesis and breakdown of PRO = ~24% Thermic Effect of Exercise (TEE) A.K.A. Energy Expenditure for Activity (EEA) All energy expended above the RMR and DIT Most variable of all the components of daily EE Voluntary Component = Exercise Involuntary Component = shivering, fidgeting, postural control Values: Up to 8,000 kcal/day for very active Much lower for sedentary (100 kcal/day) Averages ~30% of daily EE, but can be upwards of 80% for very active individuals 12

13 Role of PA in Energy Balance Energy Balance Difference between energy intake & expenditure Usually calculated for longer periods of time Positive = Intake> Expenditure Negative = Intake < Expenditure 13

14 Various Sports Energy Intakes Energy Cost of Different Activities 14

15 Energy Cost of Activities/Minute Lower Limits of EE Some athletes in various sports exhibit very low levels of energy intake. Gymnasts, bll ballet dancers, ice dancers Energy intake can be as low as 1,000 to 2,000 kcal/day even though the level of activity is quite high Can be as low as 1.2 to 1.4 times the RMR Sedentary is 1.4 to 1.6 times RMR Why so low? Desire for certain body composition profile Food consumption so low that DIT and RMR might be reduced Effects on nutrient status 15

16 Upper Limits of EE Various sports exhibit extremely high EE s and thus energy intake must be high to maintain energy balance Example: Tour de France ~ 6,000 kcal/day EE (up to 9,000 kcal/day) Energy intake must be equally high to maintain performance, but that is challenging: Limited time for eating Depressed hunger feelings GI problems related to high energy consumption Other sports: Norwegian CC skiers ~ 8,600 kcal/day Ultra Endurance runner ~ 10,750 kcal/day Tour de France Energy Balance Example 16

17 REVIEW: Find a Friend and discuss Something you need to re readread Something you are confident about REVIEW: Energy II What type of energy expenditure assessment uses [O 2 & CO 2 ] in expired respiratory gases? Intake < Expended =? Energy balance? 17