The need for energy
Energy is required for:• the basal requirements which keep the body
alive. This is known as the Basal Metabolic
Rate (BMR)
• movement – muscle contraction
• Synthesis of enzymes and other cellular materials
to allow growth and repair of body tissues.
• Pregnancy and lactation.
Energy comes from the foods we eat: CHO, fat,
protein, and is released in respiration to produce
Energy measurement
16 kJ per gram
37 kJ per gram
17 kJ per gram
29 kJ per gram
To find out how much energy a particular food provides,
the food is burnt in a bomb calorimeter. This breaks the
chemical bonds holding the atoms together resulting in
the release of heat energy which can be measured
Used to ensure even
distribution of heat
to give accurate
measurement of
temperature changes
by thermometer
Used to light food in
sealed chamber
Chamber highly
insulated to prevent
heat loss
Food burned
in pure oxygen to
release all available
Energy Balance
When the energy obtained from
food equals the total amount of
energy expenditure, the body is in
energy balance.
Negative energy balance
When the diet
provides less energy
then the body needs,
the fat stores are
used to make up for
this energy deficit
and the person loses
weight – a negative
energy balance.
Positive energy balance
• This is when the
diet provides more
energy then the
body is using.
Excess is stored as
fat and the person
gains weight.
Dietary recommendations for
• A small positive energy balance over a long
period of time will lead to being
overweight, obese, and so increases CVD,
high BP, stroke and type 2 diabetes
• There has been a marked increase in obesity
levels in the U.K in the last 50yrs,
particularly in the last 10-20 yrs.

Lesson 14 Energy balance and measurement