Energy Balance

Prof. K. Sivapalan

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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.

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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

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Energy Transfer

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Energy for Growth

• Body composition:• Water 60 %.• Protein 18-20 % [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

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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 4.184 joules

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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.

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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.

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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 = CO2 produced / O2 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 CO2 excreted / O2 intake. This can be different from RQ.

Energy Equalance of Oxygen

• When metabolized in 1 liter of oxygen, the amount of energy released:

• Glucose- 5.01 Calories• Fat- 4.7 Calories• Protein- 4.6 Calories

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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.

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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

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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.

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Metabolic Need. [Heat Output]

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Metabolic Rate.

• Amount of energy utilized per unit time per unit body weight or body surface area.

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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.

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Basal Metabolic Rate.

• Metabolic rate at basal conditions-• Post absorptive state.• Physically and mentally relaxed.• Comfortable environmental temperature.• Minimal clothing.• 40 kcal/m2/h.• BMR = 3.52W0.75

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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.

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Energy Requirement.

• Depends on metabolic rate and factors that affect it.

• Adult males- 2000-3000 kcal/day• Adult females- 1800-2500 kcal/day

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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.

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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.

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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.

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Regulation of energy expenditure.

• ? Brown adipose tissue.- [ temperature regulation in babies]

• Determined by energy requirement.

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Obesity and wasting.

• Body mass index: Wt[Kg] / Ht [M2]– 20 – 25 normal.– 25 – 30 towards obesity.– Above 30 – obesity.

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Starvation.