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Energy needs
Energy needs

Energy is require for all basic physiological
functions
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Breathing
Digestion
Excretion
Muscle function
 mobility
 heart
Brain - most energy demanding
Active transport pumps (cellular level)
Energy needs:
Units of measure of energy
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Calories:
Traditional unit
One calorie of heat raised the temperature of 1g of water
through 1°C
Other Units
1 kilocalorie = 1000 calories
Joules
 SI unit
 measure of energy exerted
1 calorie = 4.18 joules
1 kcal = 4.28 kJ
Energy needs:
How Much Energy do we need
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We need to provide, from our food enough energy to;
 Provide for body functioning
 Maintain our temperature
 Sustain physical activity
No more, no less
If take in too little energy, the body uses reserves it has put
by and we lose weight
If we take in too much energy, the body stores the excess
food, usually as fat and we put on weight
Energy needs:
Measurement of Energy Intake
Food possesses energy
 Energy is released when food is converted,
ultimately into Carbon dioxide and water
 Energy content depends on food consumed
 Total energy available is a function of Quantity of
food consumed
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Energy needs:
Measurement of Energy Intake
Different foods provide different amounts
of energy for a given weight
 Determined
by composition of food
 The following contribute to the energy content:
 Carbohydrate
 Fat
 Protein
 Alcohol
Energy needs:
Measurement of Energy Intake
The following do not contribute to the
energy content:
 Vitamins
 Mineral
 Water
 Various
methods have been developed to
determine the energy content of food
Energy needs:
Measurement of Energy Intake
Bomb Calorimeter
 Food is ignited electrically in the presence of
oxygen
 Heat of combustion is measured from a rise in
water temperature
 Heat of combustion represents the gross energy
of the food
 Energy lost during digestion and absorption
 Affected by illness
Energy needs:
Measurement of Energy Intake
Bomb Calorimeter
Energy needs:
Measurement of Energy Intake
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Proximate Principles
 The amount of energy which the body receives
from food is known as metabolised energy
 Calculated from Proximate principles
 These are standardised energy contents of food
based on typical composition
 Found from on food composition tables
Energy needs:
Measurement of Energy Intake
Metabolic Energy yields
KJ/g
Kcal/g
Fat
37
9
Alcohol
29
7
Carbohydrates
17
4
Protein
16
4
Energy needs:
Measurement of Energy Intake
100g of Potato crisps contain:
 49.3 g of Carbohydrates
 37.6g of Fat
 5.6g of Protein
 49.3 x 16 = 788.8 kJ from Carbohydrate
 37.6 x 37 = 1391.2 kJ from fat
 5.6 x 17 =95.2 kJ from protein
 Total
2275.2 kJ
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Energy needs:
Measurement of Energy Intake
% Energy from carbohydrates, protein and fat
Food
Total energy
% Energy
content of
from
serving (kJ) 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 needs:
Measurement of Energy Intake
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Diet Surveys
 Dietary and nutritional survey of British Adults
(Gregory 1990)
 Average UK dietary energy intake
 Men 10.2 MJ
 Women 7.02MJ
Energy needs:
Measurement of Energy Intake
Sources of energy in the British diet (adults)
Energy needs:
Measurement of Energy Output
Energy Output
Energy of food
 50% efficiency
ATP + Heat Loss
ATP
 50% efficiency
“Work” + Heat Loss
“Work”
Heat
Energy needs:
Components of Energy Output
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Basal metabolic rate
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Largest daily energy output
Definition: “the sum total of minimal activity of all tissue cells of
the body under steady state conditions”
Osmotic pumps
Protein synthesis
Heart
Respiratory system
Digestive tract
Thermogenesis (Temperature maintenance)
Physical activity
Growth
Energy needs:
Basal Metabolic Rate
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Body weight
 Larger the body greater BMR
 Lean body mass
 Fat mass
Age
 BMR highest in young infants
 Falls with increase in age
 2% per decade after age of 30
 Decline in activity and proportion of lean tissue
Energy needs:
Basal Metabolic Rate
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Disease
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Thyroid
Fever
Trauma
Stress
Drugs
 increase
 decrease
Undernutrition
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Gender
 Women 10% higher
body fat than men
 BMR lower for women
 Pregnancy
 Lactation
Other Factors
 Genetics
 Climate
 Ethnicity
Energy needs:
Basal Metabolic Rate
BMR (Mj/day)
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
Males
W = body weight (kg)
BMR example
A woman 40 years old, weight 62kg
 = (0.034 x 62) + 3.538
 =2.108 + 3.538 = 5.646
 =5.7 MJ/day
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Energy needs:
Components of Energy Output
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Physical Activity
 Most control
 Differing levels of activity
 Energy expended relates to body size
 Physical activity ratios (PARs)
 Physical activity level (PALs)
Energy needs:
Components of Energy Output
Energycost of an activityper hour
PAR 
Energycost of BMR per hour
Energy required over 24 hours
PAL 
BMR over 24 hours
Energy needs:
Physical Activity Ratios
Activity
PAR
Sleep
1.0
Quiet sitting
1.2
Active sitting
1.6
Stationary standing
1.6
General Mixed (personal activities)
1.4
Activities requiring moving about
2.1
Walking
2.8
Gardening
3.7
Swimming
4.8
Running
6.0
Energy needs:
Physical Activity Ratios
Bill is aged 40 and weighs 70kg
 His BMR is calculate as follows:
 (0.048 x 70) + 3.653 = 7.01MJ per day
 Therefore: His hourly BMR =7.01/24 292kJ/hour
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Energy needs:
Physical Activity Ratios
He records his daily activity pattern
 Sleeping
7hours
 Driving
2hours
 Personal activities
3 hours
 Watching TV
3hours
 Playing football
1 hour
 At work sitting at desk
8 hours
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Energy needs:
Physical Activity Ratios - Example
Activity
Sleeping
Driving
Personal activities
Watching TV
Playing Football
Sitting at work
Duration
7
2
3
3
1
8
PAR
Duration x PAR
1
7
1.6
3.2
1.4
4.2
1.2
3.6
6
6
1.2
9.6
TOTAL
33.6
BMR/hr = 292 kJ/hr
Total Energy use = 33.6 x 292 = 9811 kJ