Nutrition and Metabolism

Metabolism Metabolism – process by which living systems acquire and use free energy to carry out vital processes Catabolism (degradation) Breakdown of nutrients and cell constituents and generation of energy (Exergonic oxidation) Anabolism (biosynthesis) Endergonic synthesis of biological molecules from simpler precursors Coupled to exergonic processes through “high-energy” compounds

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 ATP Generated Provides Energy FOR

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)

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

Energy needs Measurement of Energy Intake Metabolic Energy Yields

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 31-44 kcal/kg

How to measure energy in food Direct Calorimetry Direct measurement of heat produced Bomb calorimeter Calculate Calories/g: 4 (CHO), 9 (Fat) ,4 (Pro) and 7 (Alch) based: lab analysis of food composition Calorie chart or nutrient database

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

Bomb Calorimeter measures heat produced when food is burned

Text view of bomb calorimeter

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

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

Energy Balance: Input vs Output

Energy Balance Energy In = Energy Out Energy In > Energy Out Weight Maintenance Energy In > Energy Out Weight Gain Energy In < Energy Out Weight Loss

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”

Energy In Food Complex social, environmental, physiological control Food composition tables Bomb Calorimetry Complex social, environmental, physiological control

Energy Out Energy of food = Body Energy = ATP Energy out: 3 main components: Basal Metabolic Rate Thermic Effect Food Physical activity

BMR > Activity > Dietary Thermogenesis

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

Energy needs Measurement of Energy Output direct calorimetry Measurement of heat loss

Energy needs Measurement of Energy Output Indirect calorimetry Utilization of oxygen Oxygen consumption is proportional to ATP synthesis Use oxygen consumption to determine heat production

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

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

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

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

James & Schofield