This document discusses nutrients and a healthy diet. It explains that the body needs carbohydrates, fats, proteins, vitamins, minerals, water, and fiber to stay healthy. It provides examples of the chemical structures and roles of each nutrient group. The document emphasizes eating a balanced diet with a variety of nutrients and limiting high-energy snacks to avoid weight gain and related health issues over time.

1. A healthy diet
Chapter 2
Biology

2. Nutrients
• A chemical that is needed by the body to keep it in good health is
called a nutrient.
• The human body needs a large number of different nutrients to keep
it healthy.
• Can you list the five groups of nutrients?
• They are:
Carbohydrates
Fats
Proteins
Vitamins and
Minerals

3. • In addition to these nutrients the body also needs water (70% of the
body)
• Water is important as it:
(a) provides support for the cells
(b) carries dissolved materials around the body and
(c) helps in controlling body temperature.
• Fibre is also needed by the body.

4. A healthy diet
• The body needs the range of nutrients mentioned previously to keep
healthy.
• Everyone should eat a balanced diet to eats those nutrients.
• Regular eating of high energy snacks (sweets, chocolate, ice-cream
and chips) between meals unbalances the diet and can lead to the
body becoming overweight.
• High energy snacks should be kept to a minimum.
• Overweight people have to make more effort than normal to move so
they tend to exercise less, which leads to heart problems over time.
• A food guide pyramid reminds you that you should eat large amounts
of foods at the bottom and small amounts from foods at the top.

7. 1) Carbohydrates
• Structure:
1) Made from the elements of
carbon, hydrogen and oxygen.
2) These atoms are linked
together to form molecules of
sugar
• There are different kinds of
sugar molecules but the most
commonly occurring is glucose.
• Glucose molecules link together
to form starch.
• Glucose and starch are the most
commonly known molecules.
• Other examples of known
carbohydrates is cellulose.

8. 2) Fats
• Structure:
Made large nos. of carbon and
hydrogen atoms linked into long
chains together with a few oxygen
atoms.
• There are 2 kinds of fat:
(a) Solid fat: Produced by animals
ex. Lard
(b) Liquid fat: Oil produced by
plants. Ex. Sunflower
oil.

9. 3) Proteins
• Structure:
Made of carbon, hydrogen,
oxygen and nitrogen atoms.
Some of the proteins also have
sulphur atoms.
The atoms of these elements
join together to form amino
acids.
Amino acids join together to
form proteins.

10. 4) Vitamins
• Structure:
Vitamins are needed in small
amounts.
• When vitamins were first
discovered they were named
after letters of the alphabet.
• Later on, when the chemical
structure of the molecules were
found out, they were given
chemical names.

11. 5) Minerals
• The body needs 20 minerals.
• Some minerals such as calcium
are needed in large amounts.
• Other minerals like zinc are
needed in tiny amounts (trace
elements)

12. How the body uses nutrients

13. 1) Carbohydrates
• Carbohydrates contain a large
amount of energy that can be
released quickly.
• They are used as a fuel to keep
the body alive.

14. 2) Fibre
• Cellulose is a carbohydrate
which makes up the walls of
plant cells.
• The cellulose in food is known as
the dietary fibre.
• It is found in foods such as:
- Whole meal bread
- Fruits and
- Vegetables

15. • We cannot digest fibre but it helps move food along the intestines.
• As the fibre moves through the large intestine bacteria feeds on it
(this adds bulk to the food).
• This helps the muscles of the large intestine push the food along.
• Fibres also take up water like a sponge and this makes the
undigested foods which form the faeces soft and easy to release from
the body.
• If a person’s diet lacks fibre, he may suffer from bowel problems
such as constipation.

16. 3) Fats
• Fat are needed for the formation
of cell membranes.
• They contain even larger
amounts of energy than
carbohydrates, but, energy is
released slower.
• In mammals fat forms a layer
under the skin to insulate the
mammal and keep them warm
in cool conditions

17. 4) Proteins
• Proteins are needed for building
the structures inside cells and in
the formation of tissues and
organs.
• They are needed for the repair
of the body, to repair damages
parts (cut skin) and to replace
tissues that are constantly being
worn away (ex. Lining of the
mouth)
• Enzymes are also made up of
proteins.

18. 5) Minerals
• Each mineral has more than one use.
• Example:
1) Calcium: a) make strong bones and teeth.
b) Needed to make muscles work.
c) Helps blood to clot.
(Lack of calcium can lead to weak bones and
high blood pressure)
2) Iron: Used to make haemoglobin.

20. 6) Water
• About 70% of a humans body is
water.
• The body can survive only for a few
days without a drink of water.
• Every chemical reaction in the body
takes place in water.
• The blood is made mainly of water
(transports blood components
around the body).
• Water cools down the body by
evaporation of sweat from the skin.

21. 7) Vitamins
• Each vitamin has one or more
use in the body.

22. Vitamin Effect on the body Good sources
A 1) Allow the eyes to see in dim light
2) Involved in making the mucus lining to the
respiratory , digestive and excretory systems
(protects against infection from micro-organisms)
Milk, liver, cod-
liver oil
B₁ (Thiamin) 1) Prevents digestive disorders
2) Prevents beriberi disease
Bread, milk,
brown rice,
soybean, potato
C Prevents scurvy disease (gums bleed and circulatory
system is damaged)
Blackcurrant,
orange, lemon,
papaya, guava
D Prevents rickets disease (bones become soft and leg
bones of children may bend).

23. The amount of nutrients in food

24. Keeping a balance
• Amount of nutrients in food has been
found out by experiments and
calculation.
• The amounts are usually for 100 g of
food.
• To remain healthy a person must eat
a balanced diet (all nutrients)

25. Malnutrition
• If a diet provides too few nutrients or too
many nutrients malnutrition occurs.
• Lack of vit. C causes scurvy.
• Lack of iron causes anemia.
• Too much protein is broken down and
converted into glycogen (carb.) which is stored
in the liver and part is turned into urea
(excreted in urine)
• Too much carbohydrates and fats causes
obesity (extremely overweight).
• Anorexia nervosa (Fear of gaining weight and
eat a little) can cause death.