Energy & Metabolism

Energy & MetabolismEnergy & Metabolism Energy derived from food we eatEnergy derived from food we eat Released in chemical reactions Released in chemical reactions

(metabolism)(metabolism) Transferred into ATPTransferred into ATP

Energy needed:Energy needed: Keep body aliveKeep body alive

– Heart beating/ breathing/ maintaining temperature etc.Heart beating/ breathing/ maintaining temperature etc. BASAL METABOLIC RATEBASAL METABOLIC RATE

ActivityActivity Growth/ repairGrowth/ repair ReproductionReproduction

Energy balanceEnergy balance

Simple EquationSimple Equation

Energy intake > Energy usage = Weight GainEnergy intake > Energy usage = Weight Gain

Energy intake < Energy usage = Weight LossEnergy intake < Energy usage = Weight Loss

Energy intake = Energy usage = No Weight Energy intake = Energy usage = No Weight ChangeChangeNeed to be able to measure energy intake, energy

usage

Energy measurement Energy measurement

Bomb calorimeter allows energy Bomb calorimeter allows energy intake to be accurately determinedintake to be accurately determined

Energy Measurement Energy Measurement (Food)(Food)

Energy content of foodEnergy content of food Measured in BOMB CALORIMETERMeasured in BOMB CALORIMETER

Well insulated box with a thermometerWell insulated box with a thermometer Food is burned in pure oxygenFood is burned in pure oxygen Heat given out determined from Heat given out determined from

temperature risetemperature rise Energy content of food expressed in Energy content of food expressed in

– kJ per gramkJ per gram

Carbohydrate 16 kJ.g-

1

Fat 37 kJ.g-

1

Protein 17 kJ.g-

1

Alcohol 29 kJ.g-1N.B. 1lb (0.5kg) of body fat contains around 15000KJ (3500 calories)

Calorie content of foodCalorie content of food

StellaStella 221221 BaileysBaileys 129129 BeerBeer 182182 VodkaVodka 5555

Aero Easter EggAero Easter Egg11091109

Big MacBig Mac492492

Quarter PounderQuarter Pounder515515

Bomb calorimeter allows energy Bomb calorimeter allows energy intake to be accurately determinedintake to be accurately determined

Energy usage – more difficultEnergy usage – more difficult

Direct CalorimetryDirect Calorimetry

All energy used by the body ultimately All energy used by the body ultimately is lost as heatis lost as heat

Measurement of heat production by a Measurement of heat production by a subject indicates the energy usagesubject indicates the energy usage

Subject placed in a large insulated boxSubject placed in a large insulated box Heat exchanger (water flowing through pipes) Heat exchanger (water flowing through pipes)

allows measurement of temperature change in allows measurement of temperature change in boxbox

Very accurateVery accurate Very expensive and difficultVery expensive and difficult

Indirect CalorimetryIndirect Calorimetry

Majority of energy (ATP) used by bodyMajority of energy (ATP) used by body from aerobic respiration.from aerobic respiration.

Measure oxygen consumptionMeasure oxygen consumption indicate energy usage by bodyindicate energy usage by body

Inspired air 20.93% oxygenInspired air 20.93% oxygen Measure oxygen in expired air (16-18%) & Measure oxygen in expired air (16-18%) &

volume of air expired over a given period of volume of air expired over a given period of timetime

Calculate oxygen consumptionCalculate oxygen consumption 1l oxygen provides approx. 20kJ energy1l oxygen provides approx. 20kJ energy Calculate energy used over period of timeCalculate energy used over period of time

CalculationCalculation

e.g.e.g. 100l air expired over 10min100l air expired over 10min 21% O21% O22 inspired air inspired air 18% O18% O22 expired air expired air

Vol. OVol. O22 in inspired air = 21% of 100l = 21l in inspired air = 21% of 100l = 21l Vol. OVol. O22 in expired air= 18% of 100l = 18l in expired air= 18% of 100l = 18l Vol. OVol. O22 used in 10 min =21-18l = 3l used in 10 min =21-18l = 3l Vol. OVol. O22 used per min = 0.3l used per min = 0.3l 1l O1l O22 provides 20kJ energy provides 20kJ energy Energy expenditure = 20 x 0.3 = 6kJ.minEnergy expenditure = 20 x 0.3 = 6kJ.min-1-1

Indirect Calorimetry Indirect Calorimetry

Still extremely accurateStill extremely accurate Portable respirometers can be wornPortable respirometers can be worn Energy expenditure for various activities Energy expenditure for various activities

can be measuredcan be measured

Values for activities available in Values for activities available in published tablespublished tables

Energy usage diary can give good Energy usage diary can give good estimate of energy expenditure through estimate of energy expenditure through a daya day

Correlating HR and EECorrelating HR and EE Oxygen delivered by CV systemOxygen delivered by CV system

As Oxygen needs As Oxygen needs HR HR Linear relationship between HR and OLinear relationship between HR and O22

consumptionconsumption (fitness/activity varies slope)(fitness/activity varies slope)

Measure HRMeasure HR Read oxygen consumption from graphRead oxygen consumption from graph Portable HR monitor (wrist watch)Portable HR monitor (wrist watch)

Inexpensive, easy, unobtrusive (no face Inexpensive, easy, unobtrusive (no face mask, nose clips etc.)mask, nose clips etc.)

Energy needsEnergy needsAge Age (yrs)(yrs)

Est. Average Est. Average Energy needs Energy needs (male)(male)

Estimated Estimated average average energy needs energy needs (female)(female)

11-1411-14 9.27 MJ/day9.27 MJ/day 7.72 MJ/day7.72 MJ/day

15-1815-18 11.51 MJ/day11.51 MJ/day 8.83 Mj/day8.83 Mj/day

19-5019-50 10.60 MJ/day10.60 MJ/day 8.10 MJ/day8.10 MJ/day

2218 kcal/day 1847 kcal/day

2754 kcal/day 2112 kcal/day

2536 kcal/day 1938 kcal/day

Energy balanceEnergy balance Simple EquationSimple Equation

Energy intake > Energy usage = Weight GainEnergy intake > Energy usage = Weight Gain Energy intake < Energy usage = Weight LossEnergy intake < Energy usage = Weight Loss Energy intake = Energy usage = No Weight ChangeEnergy intake = Energy usage = No Weight Change

Two ways to achieve energy balanceTwo ways to achieve energy balance Reduce intakeReduce intake Increase outputIncrease output

Easier to increase usage!!!!!!!Easier to increase usage!!!!!!! Extreme Calorie reduction diets NOT very good when only strategy Extreme Calorie reduction diets NOT very good when only strategy

usedused Obesity on increaseObesity on increase

Energy consumption decreasing in diet!Energy consumption decreasing in diet!

Dietary Energy Dietary Energy RecommendationsRecommendations

Reduce FAT intakeReduce FAT intake Fat – energy denseFat – energy dense Reduce from 38% to 30%Reduce from 38% to 30% Fat substitute - OLESTRAFat substitute - OLESTRA

Increase COMPLEX carbohydrateIncrease COMPLEX carbohydrate Increase from 47% to 50%Increase from 47% to 50%

Change in dietary mix requiredChange in dietary mix required

Food Standards Agency

Changing Energy Changing Energy expenditureexpenditure

Energy expenditure depends on:Energy expenditure depends on: Basal metabolic RATEBasal metabolic RATE Thermic effect of FOODThermic effect of FOOD Physical ActivityPhysical Activity

BASAL METABOLIC RATEBASAL METABOLIC RATE

Regulated by:Regulated by: Body SizeBody Size

Bigger bodies bigger BMRBigger bodies bigger BMR Body CompositionBody Composition

Lean tissue uses more energy than Lean tissue uses more energy than adipose (fatty) tissueadipose (fatty) tissue

For a given weight a more muscular For a given weight a more muscular individual has a higher BMR than a fatter individual has a higher BMR than a fatter individualindividual

BASAL METABOLIC RATEBASAL METABOLIC RATE

Regulated by:Regulated by: AgeAge

As age increases BMR decreases (2% per As age increases BMR decreases (2% per decade)decade)

SexSex BMR higher in malesBMR higher in males Females have more fat (25-30% c.f. 12-Females have more fat (25-30% c.f. 12-

15%),15%), less metabolically active tissueless metabolically active tissue

BASAL METABOLIC RATEBASAL METABOLIC RATE

Regulated by:Regulated by: Nutritional StatusNutritional Status

BMR decreases on a low energy intakeBMR decreases on a low energy intake Loss of lean tissue reduces BMRLoss of lean tissue reduces BMR

– Survival adaptive mechanismSurvival adaptive mechanism

Typically BMR ~50cal per hour Typically BMR ~50cal per hour (200KJ.h(200KJ.h-1-1))

Thermic effect of FoodThermic effect of Food Digestion of food uses energyDigestion of food uses energy

Fats use 3% of their energy contentFats use 3% of their energy content Carbohydrates use 9% of their energy contentCarbohydrates use 9% of their energy content Proteins use 17% of their energy contentProteins use 17% of their energy content

For a high fat diet – most energy is made For a high fat diet – most energy is made available to bodyavailable to body

This energy is stored (fat) or has to be This energy is stored (fat) or has to be usedused Reduce fat in diet, increase Carbohydrate & Reduce fat in diet, increase Carbohydrate &

protein and get a double whammyprotein and get a double whammy Protein/ CHO – 50% energy content per gramProtein/ CHO – 50% energy content per gram Use up 17%/9% of their energy in digestionUse up 17%/9% of their energy in digestion

Physical activityPhysical activity

Easiest of allEasiest of all Energy needed for activity depends on:Energy needed for activity depends on:

Individual body sizeIndividual body size– (heavier more energy needed)(heavier more energy needed)

Type of activityType of activity– See table p34See table p34

Intensity Intensity & & durationduration– Squash uses 42kJ/minSquash uses 42kJ/min– Golf uses 16.7 kJ/minGolf uses 16.7 kJ/min

Round GOLF uses more energy then 30 min squashRound GOLF uses more energy then 30 min squash– 3010 kJ c.f 1260 kJ3010 kJ c.f 1260 kJ

•Pedal an exercise bike for 13 minutes.

•Practice some fast dance steps for 16 minutes.

•Work in the garden for 18 minutes.

•Walk briskly for 22 minutes (3.5 mph).

•Clean the house for 25 minutes

•All use 100 calories (420KJ)

Benefits of Exercise for Energy Benefits of Exercise for Energy consumption/body consumption/body compositioncomposition

Energy expended in activity is used, not storedEnergy expended in activity is used, not stored Following exercise energy consumption Following exercise energy consumption

remains elevated for some timeremains elevated for some time Post exercise oxygen consumption Post exercise oxygen consumption (EPOC)(EPOC) 20-100kJ additional energy expended20-100kJ additional energy expended Oxygen needed to replenish glycogen storesOxygen needed to replenish glycogen stores Duration of EPOC is increased with more intense exerciseDuration of EPOC is increased with more intense exercise

Exercise mayExercise may increase increase BMR for a few days BMR for a few days afterwards afterwards Regular exercise is therefore importantRegular exercise is therefore important

Change in body compositionChange in body composition Lean tissue higher BMR than fattyLean tissue higher BMR than fatty

Body CompositionBody Composition

Body massBody mass Poor indicator of patient health (prognosis)Poor indicator of patient health (prognosis) Muscle (desirable – heavy), adipose Muscle (desirable – heavy), adipose

(undesirable – light)(undesirable – light) Better indicator is body compositionBetter indicator is body composition

Useful to:Useful to: Assess health risk for patientAssess health risk for patient Monitor weight lossMonitor weight loss

– Diseases/ dietingDiseases/ dieting Monitor trainingMonitor training

Estimating Body Estimating Body CompositionComposition

Body mass Index (BMI)Body mass Index (BMI) BMI=weight / (height)BMI=weight / (height)22

Weight (kg), height (m)Weight (kg), height (m)

e.g.e.g. Weight = 101kg; Height = 1.82mWeight = 101kg; Height = 1.82m

BMI=101/(1.82)BMI=101/(1.82)22

BMI=30.5BMI=30.5 Overwieght – 25.0-29.9Overwieght – 25.0-29.9 Obese Class I – 30.0-34.9Obese Class I – 30.0-34.9

BMIBMI

Easy, quickEasy, quick Unreliable (for some people)Unreliable (for some people)

Large muscle bulk classified as obese Large muscle bulk classified as obese because heavy, but still low fatbecause heavy, but still low fat

Unusual frame – very tall/ small Unusual frame – very tall/ small misclassifiedmisclassified

Measuring Body Measuring Body CompositionComposition

Body consists of two partsBody consists of two parts Fat mass (fatty tissues)Fat mass (fatty tissues) Fat free mass (muscles, bones, water Fat free mass (muscles, bones, water

etc.)etc.)

DENSITOMETRYDENSITOMETRY

Fat mass density= 1.1g/cmFat mass density= 1.1g/cm33

Fat free mass density = 0.9g/cmFat free mass density = 0.9g/cm33

%fat = 495/density - 450%fat = 495/density - 450 Body density = body mass/ body Body density = body mass/ body

volumevolume Body volume obtained by Body volume obtained by

underwater weighing (Archimedes’ underwater weighing (Archimedes’ principle)principle)

Underwater weighing to Underwater weighing to obtain volume of bodyobtain volume of body

Air expelled from lungsAir expelled from lungs Residual lung capacity (unexpired air volume Residual lung capacity (unexpired air volume

calculated)calculated) Body totally submerged, whilst sitting underwater Body totally submerged, whilst sitting underwater

on a seat suspended from a weigh machine – on a seat suspended from a weigh machine – weight underwater (kg)weight underwater (kg) Difference between weight in air and weight underwater Difference between weight in air and weight underwater

= weight of water displaced (Archimedes Principle)= weight of water displaced (Archimedes Principle) Density of water = 1kg/lDensity of water = 1kg/l Volume of water displaced (l) = weight of water Volume of water displaced (l) = weight of water

displaced (kg)displaced (kg) Volume of water displaced = volume of bodyVolume of water displaced = volume of body Correct for residual lung capacityCorrect for residual lung capacity

CalculationCalculation

60kg person, weighs 2kg 60kg person, weighs 2kg underwaterunderwater Volume of water displaced 58lVolume of water displaced 58l Density = 60/58Density = 60/58 1.0345g/cm1.0345g/cm33

%fat = 495/density – 450%fat = 495/density – 450 = 495/1.0345-450= 495/1.0345-450 =28.5%=28.5%

Bod PodBod Pod

Air displacement methodAir displacement method Assess body volume by measuring Assess body volume by measuring

volume of air displacedvolume of air displaced

ComparisonComparison

BOD PODBOD POD ExpensiveExpensive Less distressingLess distressing

Very accurateVery accurate

UNDERWATER UNDERWATER weighingweighing ExpensiveExpensive DistressingDistressing Complex, difficult & Complex, difficult &

time consumingtime consuming

Very accurateVery accurate

Skinfold ThicknessSkinfold Thickness Widely usedWidely used

Calipers used to measure thickness of skinfold Calipers used to measure thickness of skinfold (pinch skin + subcut. Fat)(pinch skin + subcut. Fat)

4 areas – triceps, subscapular, supra iliac, biceps4 areas – triceps, subscapular, supra iliac, biceps Sum calculatedSum calculated

Tables consulted to indicate % body fatTables consulted to indicate % body fat Quick, cheap, relatively easy (but practice Quick, cheap, relatively easy (but practice

required)required) May not be accurate for unusual individualsMay not be accurate for unusual individuals Difficult in very lean/ obese Difficult in very lean/ obese

Bioelectrical Impedance Bioelectrical Impedance AnalysisAnalysis

Fat is an insulatorFat is an insulator Fat free mass is conductiveFat free mass is conductive

Electrical conductivity of body will indicate Electrical conductivity of body will indicate fat contentfat content

BIA – attach electrodes to feet/ handsBIA – attach electrodes to feet/ hands Measure conductivityMeasure conductivity Easy (unskilled), quickEasy (unskilled), quick Affected by hydration levelAffected by hydration level Inaccurate in lean/ obeseInaccurate in lean/ obese

Waist/ hip ratioWaist/ hip ratio Empirical observation thatEmpirical observation that

Android (apple) – at risk of CHD, NIDDM (non-insulin Android (apple) – at risk of CHD, NIDDM (non-insulin dependent diabetes mellitus)dependent diabetes mellitus)

Gynoid (pear) – less risk of CHD, NIDDMGynoid (pear) – less risk of CHD, NIDDM Measure waist/hipt circumferenceMeasure waist/hipt circumference Hips smaller than waist (android)Hips smaller than waist (android)

Suggests extra abdominal fatSuggests extra abdominal fat Hips greater than waist (gynoid)Hips greater than waist (gynoid) Waist at belly button:Waist at belly button:

Men 37-40in, Equivalent risk as BMI of 25-30; Over Men 37-40in, Equivalent risk as BMI of 25-30; Over 40in, Equivalent risk as BMI >3040in, Equivalent risk as BMI >30

Women 32-35in, >35in resp.Women 32-35in, >35in resp.

OBESITYOBESITY

Obesity = A chronic condition Obesity = A chronic condition characterised by excessively high characterised by excessively high body fat in relation to lean tissuebody fat in relation to lean tissue

BMI > 30kg/mBMI > 30kg/m22

On the increaseOn the increase Desirable 12-15% fat, male 20-Desirable 12-15% fat, male 20-

30% fat, female 30% fat, female

14% MEN

17% WOMEN

20% CHILDREN

OBESITY – Health RisksOBESITY – Health Risks

CHD – coronary heart diseaseCHD – coronary heart disease TYPE 2 (non- insulin dependent) TYPE 2 (non- insulin dependent)

diabetes mellitusdiabetes mellitus Cancers (colon, breast)Cancers (colon, breast) Bone & joint disordersBone & joint disorders Respiratory problemsRespiratory problems

OBESITY - CausesOBESITY - Causes

Reduced physical activityReduced physical activity High, energy dense fat in dietHigh, energy dense fat in diet

Genetic, metabolic & psychological Genetic, metabolic & psychological factors also may play a part factors also may play a part

OBESITY – TreatmentOBESITY – Treatment

Reduce energy intake Reduce energy intake

OrOr

Increase energy usageIncrease energy usage

OrOr

BOTHBOTH

Recap – Recap – Benefits of Exercise for weight Benefits of Exercise for weight ControlControl

Calorie reduction more successful if exercise Calorie reduction more successful if exercise included in weight control programme:included in weight control programme:

Exercise benefits:Exercise benefits: Increased energy usageIncreased energy usage More fatty tissue lost, (active) lean tissue augmentedMore fatty tissue lost, (active) lean tissue augmented BMR maintained (possibly increased), reducing calorie BMR maintained (possibly increased), reducing calorie

intake decreases BMRintake decreases BMR

Exercise need not be vigorousExercise need not be vigorous Long duration, moderate intensity (brisk Long duration, moderate intensity (brisk

walk)walk) HEBS – 30min exercise over most days HEBS – 30min exercise over most days