Introduction to nutrients
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Learning objectives
• To introduce macronutrients and micronutrients.
• To explain the functions and sources of
carbohydrate, protein and fat.
• To explain the functions and sources of different
vitamins and minerals.
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Nutrients
Our body needs energy and nutrients from food and drinks to:
• stay alive
• be active
• grow
• keep warm.
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Nutrients
Food is eaten and digested in the body to allow the absorption of energy
and nutrients.
There are two different types of nutrients:
1) macronutrients;
2) micronutrients.
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Macronutrients
There are three different types of macronutrients essential for health.
These are:
• carbohydrate;
• protein;
• fat.
Macronutrients are measured in grams (g).
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Energy
Energy is provided by the carbohydrate, protein and fat present in the
food and drinks we consume. It is measured in kilojoules (kJ). Energy
can also be expressed as calories or kcal
1 gram of carbohydrate provides 16kJ.
1 gram of protein provides 17kJ.
1 gram of fat provides 37kJ.
.
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Carbohydrate
Carbohydrate provides the major source of energy for the body.
There are three types of carbohydrate: monosaccharides, disaccahrides
and polysaccharides.
Carbohydrate provides 16kJ (4kcal) per gram.
The two main types of carbohydrate are:
1) sugar;
2) starch.
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Sources of carbohydrate
Some examples of food sources of the sugar type of carbohydrate are:
Table sugar (sucrose)
Fruit (fructose)
Milk (lactose)
Some examples of food sources for starchy carbohydrate are:
bread
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rice
potatoes
pasta
cereal
Protein
Protein provides amino acids (building blocks of proteins), some of which
the body cannot make itself.
It is needed for growth, development and repair of the body. There is an
extra requirement for protein for growth in infants and children and for
pregnant and breast feeding women.
Protein provides 16kJ (4kcal) per gram.
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Sources of protein
Protein is found in meat, fish, eggs, poultry and dairy foods.
Protein is also found in non-meat sources, e.g. cereal products, tofu,
nuts, beans and pulses.
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Fat
Fat provides essential fatty acids (that the body cannot make itself)
which are needed for health in small amounts. It also provides energy.
Fat is a carrier for the important fat-soluble vitamins A, D, E and K.
Fat also provides protection for the major organs in the body.
One gram of fat provides 37kJ (9kcal).
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Fat
Fat is made up of fatty acids and glycerol.
Types of fatty acids include:
• Saturated;
• Unsaturated;
- Monounsaturated;
- Polyunsaturated.
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Sources of fat in the diet
Saturated fat can be found in meat, coconut oil, palm oil, butter, ghee,
lard, cream, ice cream, cheese, pastries, cakes and biscuits.
Monounsaturated and polyunsaturated fat can be found in rapeseed oil,
olive oil, oily fish, avocado and some margarines and low fat spreads.
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Micronutrients
The micronutrients are divided into:
• vitamins;
• minerals.
Micronutrients are needed in smaller amounts. These are measured in
milligrams (1mg = 0.001g) and micrograms (1μg = 0.001mg).
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Vitamins
Vitamins are found in a wide variety of foods and they have many uses
within the body.
There are two groups of vitamins:
• Fat-soluble vitamins, e.g. vitamins A, D, E and K.
• Water-soluble vitamins, e.g. B vitamins and vitamin C.
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Fat-soluble vitamins: Vitamin A
Vitamin A is needed for the normal structure and functioning of body
linings and is also involved in keeping the immune system healthy.
Vitamin A is important for vision in dim lighting. Night blindness may
develop if a deficiency occurs.
Vitamin A is found in liver, whole milk, dark green leafy vegetables,
carrots and orange coloured fruits.
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Fat-soluble vitamins: Vitamin D
Vitamin D is needed for the absorption of calcium and phosphorus from
foods which helps to keep bones healthy.
A lack of vitamin D causes rickets in children, where the legs are bent,
and causes osteomalacia in adults, which causes pain in the bones and
muscle weakness.
Most vitamin D is absorbed through the action of sunlight on our skin
during the summer months. Food sources of vitamin D include oily fish,
eggs, fortified breakfast cereals, red meat and margarine.
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Fat-soluble vitamins: Vitamin E
Vitamin E acts as an antioxidant to protect the cells in our bodies
against damage.
Good sources of Vitamin E include plant oils such as soya, corn and
olive oil, nuts, seeds and wheatgerm.
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Fat-soluble vitamins: Vitamin K
Vitamin K is needed for the normal clotting of blood and is required for
normal bone structure.
Good sources include green leafy vegetables, meat and dairy products.
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Water-soluble vitamins: B vitamins
B vitamins are water soluble and needed for the
release of energy from food.
There are many different B vitamins and each has a
specific function in the body.
The B vitamins can be found in a variety of foods,
such as bread, cereals, milk, meat, eggs, and
fortified breakfast cereals.
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Water-soluble vitamins: Vitamin C
Vitamin C acts as an antioxidant and is important for the
normal structure and functioning of body tissues. Vitamin
C is needed for the production of collagen, an important
protein which helps bones to grow and wounds to heal.
It also helps the body absorb iron from non-meat sources
such as vegetables.
Good sources of vitamin C include citrus fruits and
berries, green vegetables, peppers, tomatoes and
potatoes (especially new potatoes).
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Minerals
Minerals have many uses in the body such as:
• forming bones and teeth
• being part of our body fluids
• helping nerves work.
The amount of different minerals needed by the body changes over time.
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Calcium
Calcium is important for the formation and maintenance
of strong bones and teeth. It is also needed for the
normal functioning of nerves and muscles. Calcium is
required for blood clotting.
Sources of calcium include milk, cheese and other dairy
products, edible soft bones of fish, green leafy
vegetables, fortified soya products and bread.
A diet with adequate amounts of calcium will reduce the
risk of developing osteoporosis.
Vitamin D helps the body to absorb calcium.
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Sodium
Sodium helps to regulate water content and the balance of
electrolytes in the body. Sodium is required for the
absorption of certain nutrients and water from the gut.
Sodium is involved in the use of energy and the normal
functioning of nerves.
Most people in the UK are eating too much sodium in their
diet. High intakes of sodium are linked to high blood
pressure which increases the risk of stroke and coronary
heart disease.
Sodium is found in very small amounts in raw foods. It is
often added as salt during processing, preparation,
preservation and serving.
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Iron
Iron is required for making haemoglobin in red blood
cells which transport oxygen around the body.
It is also required for normal metabolism and the
functioning of enzymes to remove waste substances
from the body.
Adolescent girls and women need more iron than boys
because they lose blood each month through
menstruation.
A lack of iron leads to iron deficiency anaemia.
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Sources of iron
Iron is found in animal and plant sources.
Iron from meat sources is easier for the body to
absorb. Vitamin C helps the body to absorb iron from
plants.
Food sources of iron include liver, red meat, beans,
nuts, dried fruits, poultry, fish, whole grains and dark
green leafy vegetables.
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