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Nutrients and
Energy in Food
Macronutrients
Micronutrients
Energy
Nutrients

Micronutrients

Vitamins and Minerals
– are need to effectively extract energy from the
macronutrients via catabolism

Macronutrients
– Protein, Carbohydrate and Lipids
–Contain stored energy
Energy Content

Carbohydrate contain 16 kj/gram

Protein contain 17 kj/gram

Fat contains 37 kj/gram

Alcohol contains 29 kj/gram
How is energy content of food
measured?
– Bomb calorimeter
 Measures the energy released when the
food is burnt.

This includes energy from indigestible foods as
well as digestible food .

The energy content of this "fibre" must be
subtracted from the bomb calorimeter
measurement.
Bomb Calorimeter
Stirrer
Ignition fuse
Water
Thermometer
Food Sample
Bomb
Water Tank
The extraction of energy from
food

Catabolism

Repackaging energy in ATP packets
– Glucose = approx 100 ATP
– But catabolism maximum yield is 38 ATP /
glucose
– as little as 0 ATP as in Brown Adipose Tissue
The rest is lost as heat
Energy Needs of the Body

Total Kilojoule Requirements
The average day can be dived into three stages:
•
Rest, Work and
Play
Energy need for each stage are
about:
•
Rest, 2000kj
Work 3-4000kj
Play 3-4000kj
•
Over all per day = from 6000kj for total bed rest
to 14,000 for a very active individual
•
The need depend on body mass and sex
Basal Metabolism
– The energy needs of the body at complete
rest
 Used for all Internal energy needs
Recycle tissue
Immunity
Body warmth
Reduced by Tissue decrease
Is not really “basal” as it can change
due to: temperature
•
and diet.
Measure of energy needs
of the body

Indirect Calorimetry
measuring the amount of CO2 breathed out .
People can have a respirometer
attached while moving

Whole body:
people can be housed in a room
connected to CO2 monitors for air In and out
Which nutrients are used
first for energy?

Actually all macronutrients are used for
energy all the time.
Different material in different tissues
eg.:
The brain needs glucose
Aerobic Muscles use fat
The liver uses mainly excess protein.
• Ideal Body Weight
Obese
Calculate Body Mass Index
(BMI)

From % Body fat
– Measured with

Skinfold thickness

buoyancy

Electrical conduction
Desire % Body Fat
Body Condition Female
 Unhealthy
<15%
 Lean
17-22%
 Normal
22-25%
 Above Average 25-29%
 Over weight
29-35%
 Obese
35+%

Male
<10%
10-15
15-18%
18-20%
20-25%
25+%
Dangers of Under and
Over weight

Framington study
– indicated obesity increased

chance of early death

cardiovascular disease

diabetes
Framington Study
From Kennel and Gordon 1974
Underweight

Framington study indicated underweight
increased
– chance of early death
– infectious disease
– cancer

Anorexia nervosa and bulimia nervosa
Energy Use In Body
Weight Loss
Dieting
Fat distribution
Effect of fat distribution
type

Andomorphs
– More likely to suffer cardiovascular
disease

Gynomorphs
– Less likely to suffer cardiovascular
disease
Benefits of Obesity

Obese people do not get osteoporosis.
This may be due to their higher insulin secretion reducing
calcium lost in the urine.
Causes of Obesity
– Nurture versus Nature
Nurture Theories
Obesity may be caused by phycology
•
Eating to satisfy :
Boredom
• Parents
•
•
Stress
•
Culture
•
Effect of age
•
Ego
 Most obese adults were slim when young
Nature Theories

Obesity caused by physiology
Dieting does not help
Muscle tone
Diet induced Thermogenesis
Glycogen storage variations
Ageing
Need large food intake to maintain Nitrogen Balance
Benefits of Obesity

Obese people do not get osteoporosis.
This may be due to their higher insulin secretion reducing
calcium lost in the urine.
Causes of Obesity
– Nurture versus Nature
Why Dieting Doesn't Work

Reduced energy intake causes the body
to adapt:

lowers “basal metabolism”

burns up fat

reduces energy using tissue
– lean body mass

When you go off the diet

use less energy

get fatter than before