Energy Balance Prof. K. Sivapalan

Energy balance2 Energy Exchange Forms of Energy: electric, heat, light, sound, mechanical, atomic and chemical energies. Law of conservation of energy –Energy can neither be created nor destroyed. –It can be converted. Energy flows from high to low levels. This can be used to get work done. In the body, as in vehicles, chemical energy is converted to mechanical and heat energies. Large amount of energy released within a short time results in explosion. Combustion in engine of vehicles yields desired work output. But if outside the carburetor, it is burnt. In the body, combustion is carried out by series of enzymes resulting in ATP and heat. ATP – energy currency of the body- high energy phosphate bond is used to energize body mechanisms.

Energy balance3 Mechanical efficiency. ME = Work done / energy used. Motor vehicles- ≈ 30 %. Easily determined by Kilometers per liter of fuel. In the body, 00 % for isometric contractions and Close to 50 % for isotonic contractions

Energy balance4

Energy balance5 Energy Transfer

Energy balance6 Energy for Growth Body composition: Water 60 %. Protein % [Energy]. Fat M-15 %, F- 25 % [Energy]. Carbohydrate 2 % [Energy]. Minerals. Total amount of the above increases as fertilized ovum grows into an adult. Body energy content increases during growth

Energy balance7 Measurement of Energy As all forms of energy can be equated, It is customary to measure it as equivalent of heat energy. Unit of Measurement: calorie, Calorie, kilocalorie, joules and kilo joules. calorie is the amount of heat needed to raise one gram of water from 15°C to 16°C Calorie = 1000 calories [kilocalorie] Calorie = 1000 x joules

Energy balance8 Measurement of energy intake. Energy consumed = energy in substances consumed [food, drinks, snacks]. Energy absorbed = energy consumed – energy in feces [unabsorbed materiels]. Energy excreted = energy in feces and urine [urea, glucose, protein]. Metaboilzable energy intake = energy consumed – energy excreted.

Energy balance9 Measurement of energy consumed Diary method. Weighing food and composition table. Energy content- heat of combustion [Calories per gram]. –Carbohydrate- 4.1[4.1] –Fat- 9.4[9.3] –Protein – 5.65[4.35] –Alcohol – 7. Samples are combusted in Bomb Calorimeter to determine exact energy content.

Energy balance10 Measurement of energy expenditure. Direct calorimetry is measuring heat output: subject is placed in insulated chamber and heat out put is measured. Lots of limitations. Indirect calorimetry is assessing energy expenditure from measurement of oxygen consumption. Energy equivalence of oxygen depends on the food combusted. Respiratory Quotient indicates the fuel. RQ = CO 2 produced / O 2 utilized in oxidation. [Carbohydrate- 1.0, protein- 0.85, and fat-0.7 ]. Actual energy equivalence can be obtained from a normogram if RQ is measured. Respiratory Exchange Ratio is CO 2 excreted / O 2 intake. This can be different from RQ.

Energy Equalance of Oxygen When metabolized in 1 liter of oxygen, the amount of energy released: Glucose Calories Fat- 4.7 Calories Protein- 4.6 Calories Energy balance11

Energy balance12 Measurement of oxygen consumption. Spirometer method. Convert to STP. [Water vapor.] Energy equivalence of oxygen [energy released by 1 liter of oxygen] is obtained from a normogram – read against R.Q. Limitations- Actual RQ cannot measured. Instrument cannot be moved. Cannot do experiment for longer period because oxygen will be consumed in short time.

Energy balance13 Use of Weir’s Formula Collect expiratory air over period of time in a Dougless bag or use a Max Plank Respirometer and measure the volume and gas concentrations. Oxygen in inspired air = Vi Oi Oxygen in expired air = VeOe. Oxygen consumption = Vi Oi – Ve Oe. Assume Vi = Ve [error] Assume RQ [error] Weir’s formula: E = Ve (Oi-Oe) 21.1 kJ [5.04 kcal] It is accurate because two opposite errors cancel out.

Prediction of Metabolic Rate Energy balance14

Energy balance15 Measurement of body energy. Carbohydrate, protein and fat are the energy containing substances in the body. Dry the body, and determine energy content by combustion of samples in bomb calorimeter. Determine body water, lean tissue and fat content and calculate energy content. Determine body fat and lean body mass using Archimedes principle or skin fold. Change in body weight of adults indicates change in body energy because it is adipose tissue. Other causes of change in body weight- Body water.

Energy balance16 Metabolic Need. [Heat Output]

Energy balance17 Metabolic Rate. Amount of energy utilized per unit time per unit body weight or body surface area.

Energy balance18 Factors Affecting the Metabolic Rate. Height, weight, surface area, sex, age Muscular exercise. Oxygen debt. Specific dynamic action. Environmental temperature.[ U shaped curve] Body temperature. Growth, pregnancy, lactation State of Conciousness [meditation, sleep ↓10% of BMR] Emotional state, thyroid function, catecholamines. Starvation ↓40 % of BMR.

Energy balance19 Basal Metabolic Rate. Metabolic rate at basal conditions- Post absorptive state. Physically and mentally relaxed. Comfortable environmental temperature. Minimal clothing. 40 kcal/m 2 /h. BMR = 3.52W 0.75

Energy balance20

Energy balance21 Specific Dynamic Action Increase in metabolism due to assimilation of food into body [heat increment of food]. 100 kcal protein increases MR by 30 kcal, carbohydrate- 6 kcal and fat- 4 kcal. SDA may last for more than 6 hours, longest for protein. Mastication, secretion, absorption, storage, metabolic stimulants.

Energy balance22 Energy Requirement. Depends on metabolic rate and factors that affect it. Adult males kcal/day Adult females kcal/day

Energy balance23

Energy balance24 Energy Balance. Energy expenditure = Energy intake ± Change in body energy content. Regulation is not by chance. If EI – EE = 50 kcal/day, deposited fat = 50/9 = 5.5 g Increase in body weight ≈ 6 g. Over a year, 6 x 365 = 2190 g. Over 20 years, 44kg - this does not happen. Evidence for the presence of regulation is indirect. Examples of positive and negative energy balances.

Energy balance25 Regulation of energy intake. Non physiological- –Flavor. –mood. Physiological- –Blood glucose. –Free fatty acids. –Distension of stomach. –CCK. –Peptide YY –ghrelin Long term- body fat- Leptin from Adipose tissue. Centre- appetite and satiety centers in hypothalamus.

Energy balance26 Regulation of body energy content. Body fat- –structural fat –constant. –storage fat. (Leptin) Body Protein: –Structural protein- constant –storage protein- labile protein. ? Sensors of Body weight.

Energy balance27 Regulation of energy expenditure. ? Brown adipose tissue.- [ temperature regulation in babies] Determined by energy requirement.

Energy balance28 Obesity and wasting. Body mass index: Wt[Kg] / Ht [M 2 ] –20 – 25 normal. –25 – 30 towards obesity. –Above 30 – obesity.

Energy balance29 Starvation.