A healthy dietChapter 2

Biology

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:CarbohydratesFatsProteinsVitamins and Minerals

• 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.

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.

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.

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.

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.

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.

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)

How the body uses nutrients

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.

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

• 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.

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

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.

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.

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.

7) Vitamins• Each vitamin has one or more

use in the body.

Vitamin Effect on the body Good sourcesA 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 disorders2) 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).

The amount of nutrients in food

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)

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.