Energy needs

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Energy needs
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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)

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Energy needsUnits of measure of energy

• Calories
• Traditional unit
• One calorie of heat raised the temperature of 1g
  of water through 1C
• Other Units
• 1 kilocalorie 1000 calories
• Joules
• SI unit
• measure of energy exerted
• 1 calorie 4.18 joules
• 1 kcal 4.28 kJ

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Energy needsHow 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

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Energy needsMeasurement 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 needsMeasurement 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

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Energy needsMeasurement 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

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Energy needsMeasurement 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

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Energy needsMeasurement of Energy Intake
Bomb Calorimeter
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Energy needsMeasurement 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

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Energy needsMeasurement of Energy Intake
Metabolic Energy yields
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Energy needsMeasurement 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 needsMeasurement of Energy Intake
Energy from carbohydrates, protein and fat
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Energy needsMeasurement 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

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Energy needsMeasurement of Energy Intake
Sources of energy in the British diet (adults)
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Energy needsMeasurement of Energy Output

• Energy Output
• Energy of food ATP Heat Loss
• 50 efficiency
• ATP Work Heat
  Loss
• 50 efficiency
• Work Heat

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Energy needsComponents 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

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Energy needsBasal 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

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Energy needsBasal 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

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Energy needsBasal Metabolic Rate
W body weight (kg)
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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 needsComponents 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)

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Energy needsComponents of Energy Output
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Energy needsPhysical 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
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Energy needsPhysical 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 needsPhysical 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 needsPhysical Activity Ratios - Example
BMR/hr 292 kJ/hr Total Energy use 33.6 x 292
9811 kJ