Energy & Metabolism
Energy derived from food we eat
 Released in chemical reactions (metabolism)



Transferred into ATP
Energy needed:

Keep body alive
– Heart beating/ breathing/ maintaining temperature etc.
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BASAL METABOLIC RATE
Activity
Growth/ repair
Reproduction
Energy balance

Simple Equation

Energy intake > Energy usage = Weight Gain

Energy intake < Energy usage = Weight Loss

Energy intake = Energy usage = No Weight Change
Need to be able to measure energy intake, energy
usage
Energy measurement

Bomb calorimeter allows energy intake
to be accurately determined
Energy Measurement (Food)
Carbohydrate

16 kJ.g-1
Energy content of food
Fat Measured in BOMB CALORIMETER
37 kJ.g-1

Well insulated box with a thermometer
 Food is burned in pure oxygen
Protein
17 kJ.g-1
Heat given out determined from
temperature rise 29 kJ.g-1
Alcohol
 Energy content of food expressed in

– kJ per gram
N.B. 1lb (0.5kg) of body fat contains around 15000KJ (3500 calories)
Calorie content of food
Stella
 Baileys
 Beer
 Vodka

221
129
182
55
Aero Easter Egg
 Big Mac
 Quarter Pounder

1109
492
515
Bomb calorimeter allows energy intake
to be accurately determined
 Energy usage – more difficult

Direct Calorimetry
All energy used by the body ultimately is lost
as heat
 Measurement of heat production by a subject
indicates the energy usage



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
Subject placed in a large insulated box
Heat exchanger (water flowing through pipes) allows
measurement of temperature change in box
Very accurate
Very expensive and difficult
Indirect Calorimetry

Majority of energy (ATP) used by body


from aerobic respiration.
Measure oxygen consumption

indicate energy usage by body

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
Inspired air 20.93% oxygen
Measure oxygen in expired air (16-18%) & volume
of air expired over a given period of time
Calculate oxygen consumption
1l oxygen provides approx. 20kJ energy
Calculate energy used over period of time
Calculation

e.g.
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100l air expired over 10min
21% O2 inspired air
18% O2 expired air
Vol. O2 in inspired air = 21% of 100l = 21l
Vol. O2 in expired air= 18% of 100l = 18l
Vol. O2 used in 10 min =21-18l = 3l
Vol. O2 used per min = 0.3l
1l O2 provides 20kJ energy
Energy expenditure = 20 x 0.3 = 6kJ.min-1
Indirect Calorimetry

Still extremely accurate

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Portable respirometers can be worn
Energy expenditure for various activities can be
measured
Values for activities available in published
tables
 Energy usage diary can give good estimate of
energy expenditure through a day

Correlating HR and EE

Oxygen delivered by CV system

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Linear relationship between HR and O2
consumption


(fitness/activity varies slope)
Measure HR

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As Oxygen needs  HR 
Read oxygen consumption from graph
Portable HR monitor (wrist watch)
Inexpensive, easy, unobtrusive (no face mask,
nose clips etc.)
Energy needs
Age (yrs) Est. Average
Energy needs
(male)
11-14
9.27 MJ/day
15-18
2218 kcal/day
1847 kcal/day
11.51 MJ/day
8.83 Mj/day
2754 kcal/day
19-50
Estimated
average energy
needs (female)
7.72 MJ/day
10.60 MJ/day
2536 kcal/day
2112 kcal/day
8.10 MJ/day
1938 kcal/day
Energy balance

Simple Equation
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Two ways to achieve energy balance

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Reduce intake
Increase output
Easier to increase usage!!!!!!!

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Energy intake > Energy usage = Weight Gain
Energy intake < Energy usage = Weight Loss
Energy intake = Energy usage = No Weight Change
Extreme Calorie reduction diets NOT very good when only
strategy used
Obesity on increase

Energy consumption decreasing in diet!
Change in
dietary mix required
Dietary
Energy
Recommendations

Reduce FAT intake
Fat – energy dense
 Reduce from
38%
to 30%
Food
Standards
Agency
 Fat substitute - OLESTRA


Increase COMPLEX carbohydrate

Increase from 47% to 50%
Changing Energy expenditure

Energy expenditure depends on:
Basal metabolic RATE
 Thermic effect of FOOD
 Physical Activity

BASAL METABOLIC RATE

Regulated by:

Body Size


Bigger bodies bigger BMR
Body Composition
Lean tissue uses more energy than adipose
(fatty) tissue
 For a given weight a more muscular individual
has a higher BMR than a fatter individual

BASAL METABOLIC RATE

Regulated by:

Age


As age increases BMR decreases (2% per
decade)
Sex
BMR higher in males
 Females have more fat (25-30% c.f. 12-15%),
 less metabolically active tissue

BASAL METABOLIC RATE

Regulated by:

Nutritional Status
BMR decreases on a low energy intake
 Loss of lean tissue reduces BMR

– Survival adaptive mechanism

Typically BMR ~50cal per hour (200KJ.h-1)
Thermic effect of Food

Digestion of food uses energy

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Fats use 3% of their energy content
Carbohydrates use 9% of their energy content
Proteins use 17% of their energy content
For a high fat diet – most energy is made
available to body
 This energy is stored (fat) or has to be used


Reduce fat in diet, increase Carbohydrate &
protein and get a double whammy

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Protein/ CHO – 50% energy content per gram
Use up 17%/9% of their energy in digestion
Physical activity
•Pedal
an exercise
 Easiest
of all bike for 13 minutes.
•Practice
someneeded
fast dance
steps for
16 minutes.
 Energy
for activity
depends
on:
Individual
size
•Work in the
gardenbody
for 18
minutes.
– (heavier more energy needed)
•Walk briskly
for
minutes (3.5 mph).
 Type
of 22
activity
– See table p34
•Clean the house for 25 minutes

Intensity & duration
Squash
uses 42kJ/min
•All use –100
calories
(420KJ)
– Golf uses 16.7 kJ/min

Round GOLF uses more energy then 30 min squash
– 3010 kJ c.f 1260 kJ
Benefits of Exercise for Energy
consumption/body composition
Energy expended in activity is used, not
stored
 Following exercise energy consumption
remains elevated for some time

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20-100kJ additional energy expended
Oxygen needed to replenish glycogen stores
Duration of EPOC is increased with more intense exercise
Exercise may increase BMR for a few days
afterwards

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Post exercise oxygen consumption (EPOC)
Regular exercise is therefore important
Change in body composition

Lean tissue higher BMR than fatty
Body Composition

Body mass

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Poor indicator of patient health (prognosis)
Muscle (desirable – heavy), adipose (undesirable –
light)
Better indicator is body composition

Useful to:

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Assess health risk for patient
Monitor weight loss
– Diseases/ dieting

Monitor training
Estimating Body Composition

Body mass Index (BMI)

BMI=weight / (height)2

Weight (kg), height (m)
e.g.
 Weight = 101kg; Height = 1.82m
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BMI=101/(1.82)2
BMI=30.5
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Overwieght – 25.0-29.9
Obese Class I – 30.0-34.9
BMI
Easy, quick
 Unreliable (for some people)

Large muscle bulk classified as obese because
heavy, but still low fat
 Unusual frame – very tall/ small misclassified

Measuring Body Composition

Body consists of two parts
Fat mass (fatty tissues)
 Fat free mass (muscles, bones, water etc.)

DENSITOMETRY
Fat mass density= 1.1g/cm3
 Fat free mass density = 0.9g/cm3
 %fat = 495/density - 450
 Body density = body mass/ body
volume
 Body volume obtained by underwater
weighing (Archimedes’ principle)

Underwater weighing to
obtain volume of body
Air expelled from lungs
 Residual lung capacity (unexpired air volume
calculated)
 Body totally submerged, whilst sitting
underwater on a seat suspended from a
weigh machine – weight underwater (kg)
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Difference between weight in air and weight
underwater = weight of water displaced
(Archimedes Principle)
Density of water = 1kg/l
Volume of water displaced (l) = weight of water
displaced (kg)
Volume of water displaced = volume of body
Correct for residual lung capacity
Calculation

60kg person, weighs 2kg underwater
Volume of water displaced 58l
 Density = 60/58
 1.0345g/cm3

%fat = 495/density – 450

= 495/1.0345-450

=28.5%

Bod Pod
Air displacement method
 Assess body volume by measuring
volume of air displaced

Comparison

BOD POD

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Expensive
Less distressing

UNDERWATER weighing
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Very accurate
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Expensive
Distressing
Complex, difficult & time
consuming
Very accurate
Skinfold Thickness

Widely used

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Calipers used to measure thickness of skinfold
(pinch skin + subcut. Fat)
4 areas – triceps, subscapular, supra iliac, biceps
Sum calculated
Tables consulted to indicate % body fat
 Quick, cheap, relatively easy (but practice
required)
 May not be accurate for unusual individuals
 Difficult in very lean/ obese

Bioelectrical Impedance
Analysis
Fat is an insulator
 Fat free mass is conductive
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Electrical conductivity of body will indicate fat
content
BIA – attach electrodes to feet/ hands
Measure conductivity
Easy (unskilled), quick
Affected by hydration level
Inaccurate in lean/ obese
Waist/ hip ratio

Empirical observation that

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Android (apple) – at risk of CHD, NIDDM (noninsulin dependent diabetes mellitus)
Gynoid (pear) – less risk of CHD, NIDDM
Measure waist/hipt circumference
 Hips smaller than waist (android)

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Suggests extra abdominal fat
Hips greater than waist (gynoid)
 Waist at belly button:
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Men 37-40in, Equivalent risk as BMI of 25-30;
Over 40in, Equivalent risk as BMI >30
OBESITY
Obesity = A chronic condition
MEN high body
characterised14%
by excessively
fat in relation to lean tissue
17% WOMEN
 BMI > 30kg/m2
 On the increase
20% CHILDREN
 Desirable 12-15% fat, male 20-30% fat,
female

OBESITY – Health Risks
CHD – coronary heart disease
 TYPE 2 (non- insulin dependent)
diabetes mellitus
 Cancers (colon, breast)
 Bone & joint disorders
 Respiratory problems

OBESITY - Causes
Reduced physical activity
 High, energy dense fat in diet


Genetic, metabolic & psychological
factors also may play a part
OBESITY – Treatment

Reduce energy intake


Increase energy usage


Or
Or
BOTH
Recap –
Benefits of Exercise for weight Control
Calorie reduction more successful if exercise
included in weight control programme:
 Exercise benefits:




Increased energy usage
More fatty tissue lost, (active) lean tissue augmented
BMR maintained (possibly increased), reducing calorie
intake decreases BMR
Exercise need not be vigorous
 Long duration, moderate intensity (brisk
walk)
 HEBS – 30min exercise over most days
