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Energy needs
Energy needs
Energy is require for all basic physiological
functions
Breathing
Digestion
Excretion
Muscle function
mobility
heart
Brain - most energy demanding
Active transport pumps (cellular level)
Energy needs:
Units of measure of energy
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
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
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
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
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
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
Basal metabolic rate
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
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
Disease
Thyroid
Fever
Trauma
Stress
Drugs
increase
decrease
Undernutrition
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
Energy needs:
Components of Energy Output
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
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
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