ENERGY BALANCE and ENERGY EXPENDITURE

M.Prasad NaiduMSc Medical Biochemistry, Ph.D,.

Learning objectives Explain and discuss energy balance

Energy intake

Energy expenditure

Energy balance Relationship between level of energy intake

and expenditureEnergy intake

○ Energy absorbed and maintained by bodyEnergy expenditure

○ Energy used in cellular metabolism or lost from excretory routes

Occurs when energy intake matches energy expenditure

Energy balance equation

Energy balance can eitherNil

○ No change in energy status and weight+ve

○ Energy surplus and potential increase in body weight-ve

○ Energy deficit and potential body weight reduction

Energy balance (%) = energy intake (kcal)/energy expenditure Energy balance (%) = energy intake (kcal)/energy expenditure

(kcal) * 100%(kcal) * 100%

E.g.

Energy intake One component of energy

equationEnergy sources

○ CHO○ protein ○ fat

alcohol

Diet assessment tools to estimate energy intake24hr recallFood diaries

Energy expenditure Other component of energy balance equation

Energy nutrients (CHO, fat, protein) broken down in tissue to power muscle contractions and other cell activitiesResulted in energy released from body in the form of

heat energy (kcal)

1kcal of heat energy○ Amount of heat required to raise temp of 1kg of H2O by 1oC =

4.184 kj

Metabolic rate describes amount of energy released in a given unit of time

Tools for assessment of energy expenditure Direct calorimetry

Metabolic chamber ○ by measuring amount of gases utilized and produced

during energy metabolism directly○ where a person enters an insulated room or metabolic

chamber for a specific periodand heat dissipated by body is measured

○ MechanismHeat release warms a layer of water or other fluid surrounding

chamber, and change in fluid temp reflects person’s energy expenditure

Indirect calorimetryi. Metabolic cart that measures VO2 and VCO2

○ where tubing connects to person while at rest or engaged in physical act

○ MechanismVolume of CO2 produced is divided by volume of O2 consumed

to yield respiratory exchange ration (RER)

- RER- used to predict the contribution made by fat and CHO to total

energy experiment, because oxidations of these nutrients are associated with different ratios of VO2 and CO2

- now used in weight management programms to better predict energy expenditure for diet prescription

ii. Doubly labelled water (DLW)Utilizes water

molecules containing stable isotopes of H2 and O2

Principle of the doubly-labelled water method

Components of Energy Expenditure (EE) Total Energy Expenditure (TEE) =

C1 ○ Resting Metabolic Rate (RMR) +

C2○ Thermic Effect of Activity (TEA) +

C3○ adaptive Thermogenesis (AT)

C1: Basal and RMR Basal metabolism (BM)

energy expended during nonactive restMeasures in a climate-controlled room 12 hrs after a meal

Basal metabolic rate (BMR)Basal metabolism during specific period e.g. 1 hour or 1 day

Resting metabolic rate (RMR)Used interchangeablyRestricts 4 hrs after meal prior to assessment or later in

day10% more than BMR

BMR or RMR Is related to homeostasis including energy

expended for cell turn over, resting heart rate and respiration, urine production, protein synthesis, nucleic acid, etc

About 50-75% or 60-75% of TEE is BMR or RMR respectively

BMR estimation Method 1. Basal energy

BMR=BWx24hrs

Method 2. BMR = 70 x BW75

Method 3. Harris-Benedict formulaMen (BMR)=66+(13.7xBW)+(5xht)-(6.8xage)Women (BMR)=655+(9.6xBW)+(1.7xht)-(4.7xage)

Method 4. FAO/WHO EquationMale (30-60)=11.6xwt+487Female (30-60)=10.5xwt+596

BMR comparison

Male has higher BMR to female due to greater skeletal muscle to adipose tissue ratioGender differences in O2 consumption (VO2)

○ Women consume ~80% of what men consume

Infant has higher BMR to adults due to greater % of FFM than adults and engaged in rapid tissue growth

C2: Thermic Effect of Activity (TEA) This is the skeletal muscle

activity where more ATP demand is required for both muscle contraction and relaxation In addition to physical

movement as walking, talking, running, climbing stairs and maintaining positions and posture

Estimation of TEA can be done by keeping an activity log over a 24hr period then apply energy equivalent

coefficients in the following table

C3: Thermal Effect of Food (TEF) Increase in energy expenditure associated with

consumption of foodRepresents increase in TEF attributed to digestion,

absorption, metabolism and storage of nutrients

Estimated to be 10% of TE intake during a day○ E.g. 250kcal from 2500kcal over a 24hr period

TEF may also be influence bySize (larger – more TEF)Composition of meals (more CHO and protein-more

TEF)

C4: Adaptive Thermogenesis (AT) Energy expenditure increase and even

decrease due to change in environmental tempt and exposure to radiant energyManipulate energy expenditure to regulate body

tempt

E.g. applicable to travel athletes to cool environment, etc

Conclusion

Energy balance

Energy intake (CHO, protein, fat)

Energy expenditure○ BMR or RMR○ TEA○ TEF

AT