Energy

1
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.
• BASAL METABOLIC RATE
• Activity
• Growth/ repair
• Reproduction

2
Energy balance

• Simple Equation
• Energy intake gt Energy usage Weight Gain
• Energy intake lt Energy usage Weight Loss
• Energy intake Energy usage No Weight Change

Need to be able to measure energy intake, energy
usage
3
(No Transcript)
4
Energy measurement

• Bomb calorimeter allows energy intake to be
  accurately determined

5
Energy Measurement (Food)
Carbohydrate 16 kJ.g-1 Fat 37
kJ.g-1 Protein 17 kJ.g-1 Alcohol 29 kJ.g-1

• Energy content of food
• Measured in BOMB CALORIMETER
• Well insulated box with a thermometer
• Food is burned in pure oxygen
• Heat given out determined from temperature rise
• Energy content of food expressed in
• kJ per gram

N.B. 1lb (0.5kg) of body fat contains around
15000KJ (3500 calories)
6
Calorie content of food

• Stella 221
• Baileys 129
• Beer 182
• Vodka 55

• Aero Easter Egg 1109
• Big Mac 492
• Quarter Pounder 515

7

• Bomb calorimeter allows energy intake to be
  accurately determined
• Energy usage more difficult

8
Direct Calorimetry

• All energy used by the body ultimately is lost as
  heat
• Measurement of heat production by a subject
  indicates the energy usage
• 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

9
Indirect Calorimetry

• Majority of energy (ATP) used by body
• from aerobic respiration.
• Measure oxygen consumption
• indicate energy usage by body
• 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

10
Calculation

• e.g.
• 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

11
Indirect Calorimetry

• Still extremely accurate
• 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

12
Correlating HR and EE

• Oxygen delivered by CV system
• As Oxygen needs ? HR ?
• Linear relationship between HR and O2 consumption
• (fitness/activity varies slope)
• Measure HR
• Read oxygen consumption from graph
• Portable HR monitor (wrist watch)
• Inexpensive, easy, unobtrusive (no face mask,
  nose clips etc.)

13
Energy needs
Age (yrs) Est. Average Energy needs (male) Estimated average energy needs (female)
11-14 9.27 MJ/day 7.72 MJ/day
15-18 11.51 MJ/day 8.83 Mj/day
19-50 10.60 MJ/day 8.10 MJ/day
2218 kcal/day 1847 kcal/day 2754 kcal/day
2112 kcal/day 2536 kcal/day 1938 kcal/day
14
Energy balance

• Simple Equation
• Energy intake gt Energy usage Weight Gain
• Energy intake lt Energy usage Weight Loss
• Energy intake Energy usage No Weight Change
• Two ways to achieve energy balance
• Reduce intake
• Increase output
• Easier to increase usage!!!!!!!
• Extreme Calorie reduction diets NOT very good
  when only strategy used
• Obesity on increase
• Energy consumption decreasing in diet!

15
Dietary Energy Recommendations
Change in dietary mix required

• Reduce FAT intake
• Fat energy dense
• Reduce from 38 to 30
• Fat substitute - OLESTRA
• Increase COMPLEX carbohydrate
• Increase from 47 to 50

Food Standards Agency
16
Changing Energy expenditure

• Energy expenditure depends on
• Basal metabolic RATE
• Thermic effect of FOOD
• Physical Activity

17
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

18
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

19
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)

20
Thermic effect of Food

• Digestion of food uses energy
• 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
• Protein/ CHO 50 energy content per gram
• Use up 17/9 of their energy in digestion

21
Physical activity

• Easiest of all
• Energy needed for activity depends on
• Individual body size
• (heavier more energy needed)
• Type of activity
• See table p34
• Intensity duration
• Squash uses 42kJ/min
• Golf uses 16.7 kJ/min
• Round GOLF uses more energy then 30 min squash
• 3010 kJ c.f 1260 kJ

22
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
• Post exercise oxygen consumption (EPOC)
• 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
• Regular exercise is therefore important
• Change in body composition
• Lean tissue higher BMR than fatty

23
Body Composition

• Body mass
• Poor indicator of patient health (prognosis)
• Muscle (desirable heavy), adipose (undesirable
  light)
• Better indicator is body composition
• Useful to
• Assess health risk for patient
• Monitor weight loss
• Diseases/ dieting
• Monitor training

24
Estimating Body Composition

• Body mass Index (BMI)
• BMIweight / (height)2
• Weight (kg), height (m)
• e.g.
• Weight 101kg Height 1.82m
• BMI101/(1.82)2
• BMI30.5
• Overwieght 25.0-29.9
• Obese Class I 30.0-34.9

25
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

26
Measuring Body Composition

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

27
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)

28
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)
• 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

29
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

30
Bod Pod

• Air displacement method
• Assess body volume by measuring volume of air
  displaced

31
Comparison

• BOD POD
• Expensive
• Less distressing
• Very accurate

• UNDERWATER weighing
• Expensive
• Distressing
• Complex, difficult time consuming
• Very accurate

32
Skinfold Thickness

• Widely used
• 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

33
Bioelectrical Impedance Analysis

• Fat is an insulator
• Fat free mass is conductive
• 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

34
Waist/ hip ratio

• Empirical observation that
• Android (apple) at risk of CHD, NIDDM
  (non-insulin dependent diabetes mellitus)
• Gynoid (pear) less risk of CHD, NIDDM
• Measure waist/hipt circumference
• Hips smaller than waist (android)
• Suggests extra abdominal fat
• Hips greater than waist (gynoid)
• Waist at belly button
• Men 37-40in, Equivalent risk as BMI of 25-30
  Over 40in, Equivalent risk as BMI gt30
• Women 32-35in, gt35in resp.

35
OBESITY

• Obesity A chronic condition characterised by
  excessively high body fat in relation to lean
  tissue
• BMI gt 30kg/m2
• On the increase
• Desirable 12-15 fat, male 20-30 fat, female

14 MEN 17 WOMEN 20 CHILDREN
36
OBESITY Health Risks

• CHD coronary heart disease
• TYPE 2 (non- insulin dependent) diabetes mellitus
• Cancers (colon, breast)
• Bone joint disorders
• Respiratory problems

37
OBESITY - Causes

• Reduced physical activity
• High, energy dense fat in diet
• Genetic, metabolic psychological factors also
  may play a part

38
OBESITY Treatment

• Reduce energy intake
• Or
• Increase energy usage
• Or
• BOTH

39
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