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Lesson 2 : Role of Metabolism in Nutrition

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  1. Lesson 2 :Role of Metabolism in Nutrition

  2. Metabolism • Metabolism – process by which living systems acquire and use free energy to carry out vital processes • Catabolism (degradation) • Nutrients and cell constituents are broken down for salvage and/or generation of energy • Exergonic oxidation • Anabolism (biosynthesis) • Endergonic synthesis of biological molecules from simpler precursors • Coupled to exergonic processes through “high-energy” compounds

  3. Role of Metabolism in Nutrition Definition: the sum of all biochemical changes that take place in a living organism. Group these reactions into two types: anabolic catabolic Reactions: require energy release energy Produce: more complex more simple compounds compounds Modus Operandi: Occurs in small steps, each of which is controlled by specific enzymes.

  4. Relationship Between Catabolic and Anabolic Pathways • Catabolic pathways • Complex metabolites are transformed into simpler products • Energy released is conserved by the synthesis of ATP or NADPH • Anabolic pathways • Complex metabolites are made from simple precursors • Energy-rich molecules are used to promote these reactions

  5. Examples of each type of metabolism: Anabolic Pathways Catabolic Pathways Protein Biosynthesis Glycolysis Glycogenesis TCA (Krebs cycle) Gluconeogenesis ß-oxidation Fatty Acid Synthesis Respiratory Chain Other useful generalizations: Some of the steps in the anabolic path (going “uphill”) may not be identical to the catabolic path--but some are shared. ATP Generated Provides Energy FOR

  6. Metabolism: Who Needs It? Average American consumes ~ 1450 lbs ( 600kg) of food each year. Assuming that 98.2% of this energy is metabolizable, 1424 lbs ( 590kg) is used to supply our needs. Supplies roughly 1 x 106 kcals/ year

  7. Energy needs Measurement of Energy Intake Diet Surveys • Dietary and nutritional survey of British Adults (Gregory 1990) • Average UK dietary energy intake • Men 10.2 MJ (2400 kcal/d) • Women 7.02MJ (1650 kcal/d)

  8. How do we employ energy? • MECHANICAL- muscle contraction • ELECTRICAL- maintaining ionic gradients (e.g., Na-K ATPase; 70% of ATP used by kidney & brain used to maintain gradient) • CHEMICAL- biotransformation of molecules (e.g., synthesis degradation, metabolism)

  9. International Unit of Energy: Joule : energy used when 1 Kg is moved 1 meter by a force of 1 Newton : kJ = 103 J; MJ = 106 J : 1 kcal = 4.184 kJ : Protein: 17 kJ or 4 kcal/g CHO: 17 kJ or 4 kcal/g Fat: 37 kJ or 9 kcal/g

  10. Energy needs Measurement of Energy Intake Metabolic Energy Yields

  11. Average Energy Needs: European text: 100 kJ/ day x BW in kg or 24 kcal/day x BW in kg American Biochem text: 129-184 kJ/ kg or 31-44 kcal/kg

  12. Conversion Efficiency: Food to Usable Energy 40% used to make high energy phosphate bonds 60% “lost” (?) as heat

  13. How to measure energy in food • Direct Calorimetry • Direct measurement of heat produced • Bomb calorimeter • Calculate • Calories/g: 4 (cho), 9 (fat) ,4 (prt) and 7 (alcohol) • based: lab analysis of food composition • Calorie chart or nutrient database

  14. Energy needs Measurement of Energy Intake Bomb Calorimeter • Food is ignited electrically in the presence of oxygen • Heat of combustion is measured from a rise in water temperature

  15. Bomb Calorimeter measures heat produced when food is burned

  16. Text view of bomb calorimeter

  17. Energy needs Measurement of Energy Intake Bomb Calorimeter • Heat of combustion represents the gross energy of the food • Energy lost during digestion and absorption • Affected by illness

  18. Energy needs Measurement of Energy Intake % Energy from carbohydrates, protein and fat

  19. Energy Balance: Input vs Output

  20. Energy Balance • Energy In = Energy Out • Weight Maintenance • Energy In > Energy Out • Weight Gain • Energy In < Energy Out • Weight Loss

  21. Energy Balance • Sources of fuel for energy • Input from diet: carbs, fat, prot, alcohol • Stored energy: glycogen, fat, muscle • Energy outgo from: • Basal metabolism • Physical activity • “Dietary thermogenesis”

  22. Energy In • Food and Beverages • Food composition tables • Bomb Calorimetry • Complex social, environmental, physiological control

  23. Energy Out • Energy of food = Body Energy = ATP • Overall efficiency 25%, 75% released heat • Energy out: • 3 main components: • Basal Metabolic Rate • Thermic Effect Food • Physical activity

  24. BMR > Activity > Dietary Thermogenesis

  25. Energy needs Measurement of Energy Output Energy Output Energy of food ATP + Heat Loss • 50% efficiency ATP “Work “+ Heat Loss • 50% efficiency “Work “ Heat

  26. Energy needs Measurement of Energy Output Energy Output • Two methods • direct calorimetry • indirect calorimetry Measurement of heat Measurement of energy used

  27. Energy needs Measurement of Energy Output direct calorimetry • Measurement of heat loss

  28. Energy needs Measurement of Energy Output Indirect calorimetry • Utilisation of oxygen • Oxygen consumption is proportional to ATP synthesis • Use oxygen consumption to determine heat production

  29. Energy needs Measurement of Energy Output Indirect calorimetry • Glucose oxidation • Starch oxidation 6H2O + 6CO 2 C6H12O6 + 6O2 + 15.5 kJ/g of energy 5nH2O + 6nCO 2 (C6H12O5)n + 6nO2 + 17 kJ/g of energy

  30. Energy needs Measurement of Energy Output Indirect calorimetry • Fat oxidation (e.g. glyceryl butro-oleostearate (main fat in butter) C3H5O3.C4H7O.C18H33O. C18H35O + 60O2 + + 43CO2 40H2O 39 kJ/g of energy

  31. Indirect calorimetry Respiratory quotient (RQ) CO 2 Produced / O 2 Consumed RQ for Carbohydrates = 1.0 RQ for fats = 0.71 (average) Energy needs Measurement of Energy Output C6H12O6 + 6O2 6H2O + 6CO 2

  32. Energy needs Measurement of Energy Output Indirect calorimetry • RQ value can be used to find the amount energy produced per litre of oxygen consumed • Metabolic mix

  33. Energy needs Measurement of Energy Output Indirect calorimetry • Respiratory Gas Analysis • Respirmeters • Direct of measurement of O2 and CO2 • Heart Rate Monitoring • Heart rate calibrated against oxygen utilisation • Isotope Method • Labelled water (2H and 18O) • Difference of rates of loss of isotopes loss of CO2

  34. What are the components of energy expenditure? 1 : Basal metabolic rate Definition: Determinants: Calculation:

  35. Energy Out: Basal Metabolism • Largest daily energy output • Definition: “the sum total of minimal activity of all tissue cells of the body under steady sate conditions” • Men estimate: lbs body weight X 11 • Women estimate: lbs body weight X 10 • affected by • Muscle > Fat Male > Female • Young > Old • Temperature: body and environment

  36. Basal Metabolic Rate • BMR = number of calories would need daily simply to stay alive if were totally inactive, in bed, awake for 16 hours & slept for 8 hours • Harris-Benedict Equation: • Women: 661+(4.38 x weight in pounds)+(4.38 x height in inches)-(4.7 x age)=BMR • Men: 67+(6.24 x weight in pounds)+(12.7 x height in inches)- (6.9 x age)=BMR

  37. James & Schofield

  38. 1) Basal Metabolic Rate • 50-70% Energy Expenditure • Maintain basic metabolic processes Cells Muscles Temperature regulation Growth • Osmotic pumps • Protein synthesis • Heart • Respiratory system • Digestive tract • Individual variation • Within individual variation 10%

  39. Factors affecting BMR • 1) Body Size & Composition • Lean tissue BMR • Body weight wt lean tissue (but also fat) • 2) Age: • age Lean tissue • 3) Sex: Men lean • 4) Activity: Exercise lean tissue

  40. Factors affecting BMR • 5) Growth BMR • Children, pregnancy • 6) Fasting/starvation: BMR • 7) Fever/stress BMR • 8) Smoking/caffeine: BMR

  41. 2 : Energy Expenditure Component : THERMIC EFFECT OF FOOD Definition: Determinants: Contribution to Total Energy Expenditure:

  42. 2) Energy Out: Dietary Thermogenesis • Dietary thermogenesis • Energy to digest, absorb, metabolize food • About 10% of calories eaten

  43. 2) Thermic Effect of Food • 3-6 hours following ingestion • ~10% energy intake • 2000 kcal diet = 200 kcal TEF • Affected by: • Meal size/frequency • Composition: Protein > Carbs/fat • Genetics

  44. 3 : Components of Energy Expenditure Physical Activity Contribution to Total Expenditure: 4 : What about accounting for changes in energy expenditure due to injury or trauma?

  45. 3) Energy Out: Physical Activity • Physical Activity affected by: • Intensity -- how vigorous • Time spent • Body weight

  46. 3) Physical Activity • Variable: 20-40% • Working muscles require energy • Heart/lung extra energy • Amt energy used depends on: • Muscle mass • Body weight • Activity nature & duration

  47. Activity Level and Metabolism • Activity can account for 20-30% of metabolism • Sedentary = Multiplier 1.15 x BMR • Light activity (Normal Every day activities) = Multiplier 1.3 x BMR • Moderately Active(exercise 3-4 x’s week) = Multiplier 1.4 x BMR • Very Active (exercise more than 4 x’s week) = Multiplier 1.5 x BMR • Extremely Active (exercise 6-7 x’s week) = Multiplier 1.6 x BMR

  48. Activity Level and Metabolism • If you change Light activity (Normal Every day activities) to Moderately Active(exercise 3-4 x’s week) daily caloric burning goes up 7.7% • If you change Light activity (Normal Every day activities) to Very Active (exercise more than 4 x’s week) daily caloric burning goes up 23% • If you change Light activity (Normal Every day activities) to Extremely Active (exercise 6-7 x’s week) daily caloric burning goes up 38.5%

  49. Full thickness Burns trauma sepsis Who Are The Critically Ill? GI Cardiac Renal Cancer