1.

3 Nutrition

Objectives

By the end of the subtopic, learners will be able to:

 Define balanced diet.

 List component of balanced diet.

 Name functions of nutrients.

Diet

 The food eaten every day by an individual or an organism is called a diet. It should
contain seven components.

 The seven required components are carbohydrates, proteins, fats, water, fibre,
vitamins and minerals.

 A diet that provides the required amounts of all the necessary nutrients in the right
proportions for healthy growth and activity is called a balanced diet.

 Dietary requirements however depend on age, sex and activity.

Age

 Growth requires an ever increasing demand for nutrients.

 Growing children need more;

o protein per unit mass of body weight than adults do because of active growth in
their bodies.

o calcium per unit mass of body weight than adults because of massive
development of bone and tooth tissue.

o iron per unit mass of body weight than adults because of higher rate of blood
production.

 Young children and teens need a protein rich diet to enable them to grow and repair
wounded tissue.
Fig 1.3.1: Playing children

Sex

 Males use up more energy than females, so they require a carbohydrate rich diet.

 Sexually mature females require diets rich in iron to replace blood lost during
menstruation.

 Pregnant women need extra nutrients for the development of the foetus:

o Proteins for cell and tissue development

o Calcium for bone development

o Iron for production of blood

Table 1.3.1: Three main nutrients in food

Nutrient made from main uses

carbohydrates simple sugars such as glucose and starch high energy source

fatty acids and glycerol high energy source

Fats

amino acids growth and repair

Proteins

 Proteins and fats are also used as an energy source if the diet lacks enough
carbohydrates in it but they are very difficult to breakdown since they are not soluble
in water easily.

 A balanced diet will also include nutrients that do not provide energy, such as:
 o Minerals like iron, to make haemoglobin in blood.

o Vitamins, such as vitamin C, which strengthens gum tissues in the mouth.

o Fibre, which improves (peristalsis) movement of food along the digestive system.

o Water, which acts as the medium for most reactions in the body.

Fig 1.3.2: A balanced diet

Carbohydrates

 A balanced diet will have enough carbohydrates to provide adequate energy for the
activities being done by the human.

 Cereals and grains form the greater source of carbohydrates for example bread, rice
(mupunga), sadza/isitshwala and potatoes (mbatatisi/amagwili)).

 Carbohydrates are first digested in the mouth when food is chewed and mixed with
 saliva.

 Saliva contains an enzyme that acts on starch, a carbohydrate.

 Carbohydrates are finally digested in the small intestine and absorbed as glucose.

 Refined sugars are absorbed more rapidly than starches.

 Refined sugars give a sudden boost of an energy source while starch that is slowly
digested may be called a slow release carbohydrate.

 Energy requirements depend mainly on the activities of the human being.

 A sports person would requires more carbohydrates to burn during exercise as

compared to an office worker who would spend a greater day seated on a computer
desk.

 If excess carbohydrates are consumed, they may be converted to a sugar called

glucose.

 Glucose may further be changed into glycogen which can be stored under the skin.

 Excess glycogen results in overweight and obesity.

 It is a condition beyond overweight where a person has accumulated too much body
fat that it might have a negative effect on their health.

Fig 1.3.3: An obese person

 Overweight people may suffer from health problems, including:

 arthritis - an illness in which the joints become worn, inflamed and painful.
 heart disease.
 breast cancer and
 diabetes - an illness in which the body is unable to control the amount of sugar in the
blood.

Lipids (fats and oils)

Fig 1.3.4: Food rich in lipids.

 Lipids are digested in the small intestines and absorbed as fatty acids and glycerol.
 They are mainly derived from animal (fats) and plant (lipids) tissue.
 Meat and animal products such as milk eggs and cheese are sources of cholesterol
and saturated fats.
 The body may store very large amounts of fats resulting in obesity.
Fig 1.3.5: Stored fats result in obesity

 An excess of cholesterol may lead to diseases of the circulatory system.

 Plant products such as peanuts and sunflower seeds provide unsaturated lipids.
 Plant lipids are usually referred to as oils because they are usually liquid at room
temperature.
 Oils and fats have a very high capacity of energy content, but are generally difficult
to breakdown in the body, because they are insoluble in water.
 Lipids provide insulation around nerve cells. They are also thermal insulators and
shock absorbers that protect essential organs in the body.
 Fats stored under the skin also act as heat insulators to help maintain the body
temperature in extremely cold times.
 Lipids may also be used by marine animals in assisting them to float well in water.
 Cholesterol from lipids forms part of cell membranes. It is however hazardous if
allowed to accumulate in the blood vessels of the heart.
 Cholesterol that has accumulated in blood vessels may cause serious circulatory
problems that may lead to cardiac arrest and elevated blood pressures.

Proteins

Fig 1.3.6: Protein rich foods

 Proteins are readily available in lean meat, fish eggs and legumes such as beans and
peas.
 Soya beans is one of the best sources of protein.
 It contains less fat and so consuming lots of soya beans would not put a person at
the risk of high cholesterol levels as compared to meat.
 Proteins are used by the body to make enzymes, structural materials such as
muscle, hormones and defence mechanisms such as antibodies.
 Proteins are very important in ensuring the development and growth of humans.
 They are digested in the stomach and small intestines where they are absorbed as
amino acids.
 Growing up children need a lot of protein.
 However in developing countries people may not get enough protein in their diet.

Fig 1.3.7: Children with kwashiorkor

 A lack of protein is called protein deficiency, it can lead to a disease called

kwashiorkor, which causes a swollen abdomen and thin limbs associated with poor
physical development.

Vitamins and minerals

 Most fresh foods contain enough vitamins to nourish humans.

 Vitamins are essential nutrients that enable the body to use other nutrients
efficiently.
 They are needed in very small amounts.
 It is good nutritional practice to start a day with fresh vegetables and fruits in order
to maintain a constant source of vitamins in your diet.

a. Zinc

 Zinc is a mineral element that plays a central role in the immune system.
 It can be found in sea food and some vegetables.
 Zinc deficiency in humans would cause growth retardation, delayed sexual and bone
maturation, skin lesions, diarrhoea, loss of appetite and poor wound healing.

b. Iron

Fig 1.3.8: Sources of iron

 Iron can be found in liver and in some vegetables such as spinach.

 Iron is a mineral that helps in the carrying of oxygen to the tissues from the lungs by
haemoglobin in red blood cell.

c. Calcium

 Calcium is usually found from edible bone tissue such as fish and cartilage, it is also
abundant in fresh milk and some milk products.
 Calcium provides the rigidity and strength of the skeleton in the form of calcium
compounds with other elements in the body.
 Calcium is the material that helps in the formation of tooth enamel.
d. Vitamin C

 Vitamin C is also referred to as ascorbic acid, it is readily available in most citrus

fruits.

 Vitamin C can also be found in cherries and some wild berries that are edible.
 It is essential in prevention of scurvy.

e. Vitamin D

 It is found in dairy products, egg, and fish liver oil.

 Vitamin D can also be made by the body under the dark skin if there is plenty of
sunlight.
 Vitamin D is needed for the absorption of calcium by the body.
 The deficiency of vitamin D may lead to a deficiency of calcium resulting in the
formation of rickets due to soft bones.

Water

 Water enables all the chemical reactions of life to take place in the body.
 Water is neither a mineral nor a nutrient. It is however very essential in our diets
because it contributes more than 66% of the human body.
 Two thirds of the water is in the cytoplasm of our cells and the other third is in our
blood plasma and tissue fluid.
 It is very important to drink adequate amounts of water to keep the water levels
balanced.
 Some excess water is lost as sweat, water vapour in exhaled air and moisture in
faeces.
 It is therefore necessary to replace lost water in the diet.
 Water can be replaced in three main ways:

o In foods such as tomatoes and salads.

o Metabolic processes such as the breakdown of carbohydrates.
o As a drink.

Dietary fibre
 It is yet another material that is not a nutrient but is of equal importance to nutrients.
 Dietary fibre is the indigestible part of food such as cellulose from plants and fibres
from fruits like mangoes.
 Plenty of fibre stretches the muscles of the gut wall helping peristalsis to push the
food more easily.
 A diet short of fibre may result in constipation which may result in bowel cancer and
a lot of other ailments of the bowels and colon.
 Constipation is an acute or chronic condition in which bowel movements occur less
often than usual or consist of hard, dry stools that are painful or difficult to pass.
 To ensure a well-balanced diet, it is important to maintain the consumption of a
variety of natural organic foods and avoid processed foods that do not contain
mixtures of nutrients and artificial none nutritive additives.

Malnutrition

 Malnutrition is eating food without correct amount of nutrients (it is eating an

unbalanced diet).
 It is also wrong nutrition, resulting from not having enough to eat, not eating enough
of the correct food, or being unable to use the food that one does eat.
 Malnutrition is different from starvation!
 Starvation is when one does not have anything to eat or is not eating enough food
for a long period of time.
 Starvation can lead to malnutrition because starving people start to eat whatever
food they find even if the food is of the same type since they want to survive.

 Malnutrition exists in two forms; undernutrition and overnutrition.

 Undernutrition is a form of malnutrition resulting from a reduced supply or deficiency
(lacking) of necessary nutrients.
 Overnutrition is a form of malnutrition whereby the intake of nutrients is
oversupplied. The amount of nutrients exceeds the amount required for normal
growth, development, and metabolism.

 Malnutrition results in:

1. Obesity due to too much food (carbohydrate, fat or protein)

2. Coronary heart disease caused by too much saturated/animal fat in the diet
which results in high cholesterol levels.

o Cholesterol can stick to the walls of arteries, gradually blocking them.

o If coronary arteries become blocked, the results can be angina and coronary
 heart disease.

3. Extreme slimming, such as those that avoid carbohydrate foods, can result in the
disease anorexia nervosa.
4. Childhood protein-energy deficiency (kwashiorkor).

Wrong proportion of nutrients for example, too much carbohydrates (starchy

foods) and a lack of protein can lead to kwashiorkor in young children.

5. Vitamin, mineral and fibre deficiency diseases.

6. Lacking key nutrients.