energy needs. energy is require for all basic physiological functions breathing digestion ...

Energy needsEnergy needs

Energy needsEnergy needs

Energy is require for all basic physiological Energy is require for all basic physiological functionsfunctions BreathingBreathing DigestionDigestion ExcretionExcretion Muscle functionMuscle function

mobilitymobility heartheart

Brain - most energy demanding Brain - most energy demanding Active transport pumps (cellular level)Active transport pumps (cellular level)

Energy needs:Energy needs:Units of measure of energy

CaloriesCalories: : Traditional unitTraditional unit One calorie of heat raised the temperature of 1g of water One calorie of heat raised the temperature of 1g of water

through 1°Cthrough 1°C Other UnitsOther Units 1 kilocalorie = 1000 calories1 kilocalorie = 1000 calories JoulesJoules

SI unitSI unit measure of energy exertedmeasure of energy exerted

1 calorie = 4.18 joules1 calorie = 4.18 joules 1 kcal = 4.28 kJ1 kcal = 4.28 kJ

Energy needs:Energy needs:How Much Energy do we needHow Much Energy do we need

We need to provide, from our food enough energy to;We need to provide, from our food enough energy to; Provide for body functioningProvide for body functioning Maintain our temperatureMaintain our temperature Sustain physical activitySustain physical activity

No more, no lessNo more, no less If take in too little energy, the body uses reserves it has put If take in too little energy, the body uses reserves it has put

by and we lose weightby and we lose weight If we take in too much energy, the body stores the excess If we take in too much energy, the body stores the excess

food, usually as fat and we put on weightfood, usually as fat and we put on weight

Food possesses energyFood possesses energy Energy is released when food is converted, Energy is released when food is converted,

ultimately into Carbon dioxide and waterultimately into Carbon dioxide and water Energy content depends on food consumedEnergy content depends on food consumed Total energy available is a function of Quantity of Total energy available is a function of Quantity of

food consumedfood consumed

Energy needs:Energy needs:Measurement of Energy Intake

Different foods provide different amounts Different foods provide different amounts of energy for a given weightof energy for a given weight Determined by composition of foodDetermined by composition of food The following contribute to the energy content: The following contribute to the energy content:

CarbohydrateCarbohydrate FatFat ProteinProtein AlcoholAlcohol


The following The following do notdo not contribute to the contribute to the energy content: energy content:

VitaminsVitamins MineralMineral WaterWater

Various methods have been developed to Various methods have been developed to determine the energy content of fooddetermine the energy content of food


Bomb CalorimeterBomb Calorimeter Food is ignited electrically in the presence of Food is ignited electrically in the presence of

oxygenoxygen Heat of combustion is measured from a rise in Heat of combustion is measured from a rise in

water temperaturewater temperature Heat of combustion represents the gross energy Heat of combustion represents the gross energy

of the foodof the food Energy lost during digestion and absorptionEnergy lost during digestion and absorption Affected by illnessAffected by illness



Bomb Calorimeter

Proximate PrinciplesProximate Principles The amount of energy which the body receives The amount of energy which the body receives

from food is known as metabolised energyfrom food is known as metabolised energy Calculated from Proximate principlesCalculated from Proximate principles These are standardised energy contents of food These are standardised energy contents of food

based on typical composition based on typical composition Found from on food composition tablesFound from on food composition tables


KJ/g Kcal/g

Fat 37 9

Alcohol 29 7

Carbohydrates 17 4

Protein 16 4


Metabolic Energy yields


100g of Potato crisps contain:100g of Potato crisps contain: 49.3 g of Carbohydrates49.3 g of Carbohydrates 37.6g of Fat37.6g of Fat 5.6g of Protein5.6g of Protein

49.3 x 16 = 788.8 kJ from Carbohydrate49.3 x 16 = 788.8 kJ from Carbohydrate 37.6 x 37 = 1391.2 kJ from fat37.6 x 37 = 1391.2 kJ from fat 5.6 x 17 =95.2 kJ from protein5.6 x 17 =95.2 kJ from protein TotalTotal 2275.2 kJ 2275.2 kJ

Food Total energy content of

serving (kJ)

% Energy from

carbohydrate

% Energy from

protein

% Energy from fat

Chocolate 1195 43 6 51

Peas 230 47 35 18

Chicken Breast 1138 0 75 24

Potato boiled 535 89 10 1


% Energy from carbohydrates, protein and fat

Diet SurveysDiet Surveys Dietary and nutritional survey of British Adults Dietary and nutritional survey of British Adults

(Gregory 1990)(Gregory 1990) Average UK dietary energy intakeAverage UK dietary energy intake Men 10.2 MJMen 10.2 MJ Women 7.02MJWomen 7.02MJ


Sources of energy in the British diet (adults)


Energy OutputEnergy OutputEnergy of food ATP + Energy of food ATP + Heat LossHeat Loss 50% efficiency50% efficiency

ATP “Work” + ATP “Work” + Heat LossHeat Loss 50% efficiency50% efficiency

““Work” HeatWork” Heat

Energy needs:Energy needs:Measurement of Energy Output

Basal metabolic rateBasal metabolic rate Largest daily energy outputLargest daily energy output Definition: “the sum total of minimal activity of all tissue cells of Definition: “the sum total of minimal activity of all tissue cells of

the body under steady state conditions”the body under steady state conditions” Osmotic pumpsOsmotic pumps Protein synthesisProtein synthesis HeartHeart Respiratory systemRespiratory system Digestive tractDigestive tract

Thermogenesis (Temperature maintenance)Thermogenesis (Temperature maintenance) Physical activityPhysical activity GrowthGrowth

Energy needs:Energy needs:Components of Energy Output

Body weightBody weight Larger the body greater BMRLarger the body greater BMR Lean body massLean body mass Fat massFat mass

AgeAge BMR highest in young infantsBMR highest in young infants Falls with increase in ageFalls with increase in age 2% per decade after age of 302% per decade after age of 30 Decline in activity and proportion of lean tissueDecline in activity and proportion of lean tissue

Energy needs:Energy needs:Basal Metabolic Rate


DiseaseDisease ThyroidThyroid FeverFever TraumaTrauma StressStress Drugs Drugs

increase increase decreasedecrease

UndernutritionUndernutrition

GenderGender Women 10% higher Women 10% higher

body fat than menbody fat than men BMR lower for womenBMR lower for women PregnancyPregnancy LactationLactation

Other FactorsOther Factors GeneticsGenetics ClimateClimate EthnicityEthnicity

BMR (Mj/day)

Males 18 – 29 0.063W + 2.896

30 – 59 0.048W + 3.653

60 – 74 0.0499W + 2.930

Females 18 – 29 0.062W + 2.036

30 – 59 0.034W + 3.538

60 - 74 0.0386W + 2.875


W = body weight (kg)

BMR exampleBMR example

A woman 40 years old, weight 62kgA woman 40 years old, weight 62kg = (0.034 x 62) + 3.538= (0.034 x 62) + 3.538 =2.108 + 3.538 = 5.646=2.108 + 3.538 = 5.646 =5.7 MJ/day =5.7 MJ/day

Physical ActivityPhysical Activity Most controlMost control Differing levels of activityDiffering levels of activity Energy expended relates to body sizeEnergy expended relates to body size Physical activity ratios (PARs)Physical activity ratios (PARs) Physical activity level (PALsPhysical activity level (PALs))



hourper BMR ofcost Energy

hourper activity an ofcost Energy PAR

hours 24over BMR

hours 24over requiredEnergy PAL

Energy needs:Energy needs:Physical Activity Ratios

ActivityActivity PARPAR

SleepSleep 1.01.0

Quiet sittingQuiet sitting 1.21.2

Active sittingActive sitting 1.61.6

Stationary standingStationary standing 1.61.6

General Mixed (personal activities)General Mixed (personal activities) 1.41.4

Activities requiring moving aboutActivities requiring moving about 2.12.1

WalkingWalking 2.82.8

GardeningGardening 3.73.7

SwimmingSwimming 4.84.8

RunningRunning 6.06.0


Bill is aged 40 and weighs 70kgBill is aged 40 and weighs 70kg His BMR is calculate as follows:His BMR is calculate as follows: (0.048 x 70) + 3.653 = 7.01MJ per day(0.048 x 70) + 3.653 = 7.01MJ per day Therefore:- Therefore:- His hourly BMR =7.01/24 292kJ/hourHis hourly BMR =7.01/24 292kJ/hour


He records his daily activity patternHe records his daily activity pattern Sleeping Sleeping 7hours7hours Driving Driving 2hours2hours Personal activities Personal activities 3 hours3 hours Watching TV Watching TV 3hours3hours Playing football Playing football 1 hour1 hour At work sitting at desk At work sitting at desk 8 hours8 hours

Energy needs:Energy needs:Physical Activity Ratios - Example

Activity Duration PAR Duration x PARSleeping 7 1 7Driving 2 1.6 3.2Personal activities 3 1.4 4.2Watching TV 3 1.2 3.6Playing Football 1 6 6Sitting at work 8 1.2 9.6

TOTAL 33.6

BMR/hr = 292 kJ/hrTotal Energy use = 33.6 x 292 = 9811 kJ

energy needs. energy is require for all basic physiological functions breathing digestion ...

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