SCIENCE FORM 2 CHAPTER 3 (3.2)

CHAPTER 2 :
NUTRITION

3.2 IMPORTANCE OF A BALANCED DIET

1. A balanced diet contains the right amount of the seven classes

of food to meet the daily requirements of the body.

2. A balanced diet is necessary for:
a. supplying the required energy
b. balanced body growth
c. maintaining the health of the body
d.preventing deficiency diseases such as scurvy and rickets

FACTOR THE GROUP REQUIRING MORE REASON
ENERGY

A.Gender Men requiring more energy of Men are more

the same age and body size active

B. Age Babies, children and teenagers This group is more

require more energy active and the life

process are faster

FACTOR THE GROUP REQUIRING MORE REASON
ENERGY
c. Body size
Big sized individuals Big sized individuals
d.Physical require more energy size require more energy
activity compared to small sized for their life process.
individuals.

An individual who does Heavy work require
heavy work uses more more energy to
energy compared to another perform.
who does light work

FACTOR THE GROUP REQUIRING MORE REASON
ENERGY

e. Weather Individuals living in places with More energy is
cold weather require more required to maintain
energy compared to individuals the body temperature
living in places with warm in a cold place.
weather

1. The calorific value of food is the total energy
produced when one gram of food is completely
burnt.

2. The quantity of energy in a food is measured in
calorie (cal) or joule (j)

1 calorie (cal) = 4.2 joule (j)
1 kilocalorie (kcal) = 4.2 kilojoules (kJ)

Energy value of main food classes

Classes of food Energy value (kJ/g)
Carbohydrates 17
18
Proteins 39
Fats

content Amount per
275 g

Carbohydrate 30.3 g

Protein 9.6 g

Fat 3.7 g

If the calorific value of rice is 16 kJ/g, what is
the calorific value in 100 g of rice??

• Solution: 100 g x 16 kJ/g = 1 600 kJ

• Example 1: The table below shows the calorific value

of certain type of food.

Food Calorific value (kJ/100g)

Rice 1500 kJ

Fried egg 950kJ

Apple 160kJ

• A boy eats 200 g of rice, 100 g of fried egg, and 50 g of apple.
• The calorific value of the boy’s breakfast is:
• (1500 x 2) + (950 ) + (160 ÷ 2) = 4030 kJ.