2. Dietary fibre (roughage)
•Dietary fibre consists mainly of cellulose that is
indigestible because we do not have enzymes to digest
•Fruits and vegetable are rich in dietary fibre.
•Importance of dietary fibre:
a.Provides bulk to the intestinal contents.
b.Stimulates peristalsis (rhythmic muscular contractions
passing along the digestive tract)
•Lack of dietary fibre in the diet leads to constipation
(failure to pass motions)
•Water is a very essential for life because 60% to 70%
of our body weight is water.
•We can survive for several weeks without food but
would be die in a few days without water.
•Importance of water:
a.Act as a solvent in which chemicals dissolve
b.Acts as a transporting agent for digested food,
excretory products, hormones and antibodies.
c.Takes part in biochemical reactions (for example,
4. d. A major component of blood, body fluids,
digestive juices and urine.
e. Regulates body temperature by
evaporation of sweat from the skin.
•We require at least 1.5 litres of water daily to
replace water lost in sweat, urine faeces and
5. The Importance of a Balance Diet
•Diet refers to the food we eat.
•A balance diet is a diet that contains all the seven classes
of food in the right amount.
•The amount of food or energy that a person needs
depends on several factors:
•Age – a teenager needs more food, especially proteins
than an old man who is no longer growing.
•Body size – people with bigger body sizes require more
energy than those with smaller body sizes.
•Sex – males require more energy than females because
males have a smaller amounts of fatty tissues in their
body. Thus, heat loss is faster in males than in females.
7. •Occupation – a person who does heavy work
needs much more energy than a person who is
only moderately active.
8. •Climate – people living in cold countries lose more
heat to their surrounding compared with those living
in the tropics. They need more energy in order to
maintain their body temperature.
9. •State of health – a person suffering from hyperthyroidism (over activity
of the thyroid gland in the neck) requires more energy.
•The amount of food eaten must balance the quantity of energy used. If
we eat too much, we will gain weight and become obese. If we eat too
little, we will lose weight. Feel weak and may suffer from difficiency
11. Calorific value of food
•The energy content of food is indicated by its calorific
or energy value.
•Carbohydrates, fats and protein supply us with
•The energy value of food is measured with a
•The unit of energy in food can be measured in
calories (cal) or joules (J) where 1 cal is equals 4.2 J.
1 cal = 4.2 J
12. Class of food Energy value (kJ g⁻₁
Energy value of carbohydrates,
proteins and fats