Macronutrients
© Food – a fact of life 2009
Extension
Learning objectives
• To understand that macronutrients are needed by
the body.
• To know the functions and sources of carbohydrate,
protein and fat.
• To understand the consequences of malnutrition of
carbohydrate, protein and fat.
© Food – a fact of life 2009
Macronutrients
The macronutrients are:
• carbohydrate;
• protein;
• fat.
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Function and sources of carbohydrate
Carbohydrate provides the main source of energy for
the body.
Some forms of complex carbohydrates may reduce
cholesterol which is beneficial for health.
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Further classification of carbohydrate
There are different ways to classify carbohydrate.
One method is into:
1) sugar;
2) starch.
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Classification of carbohydrate
Sugar
Monosaccharides are the simplest form of
carbohydrate molecules, e.g. glucose, fructose and
galactose.
Disaccharides are formed when two sugar molecules
join together, e.g. sucrose (glucose and fructose),
lactose (glucose and galactose) and maltose (2
molecules of glucose).
Starch
Polysaccharides are made up of many
monosaccharide's molecules joined together, e.g.
starch, glycogen, cellulose and pectin.
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Another classification systems for sugars
Intrinsic can be described as sugars incorporated into
the cellular structure of food,
e.g. sugars in whole fruits and vegetables.
Extrinsic sugars can be described as not bound into
cellular structure,
e.g. lactose in dairy products.
Non-milk extrinsic sugars (NMES) are sugars not bound
into cellular structure and also not found in milk,
e.g. honey, fruit juices, table sugar and confectionery
are all examples of foods containing NMES.
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Excessive consumption of carbohydrate
Increased body weight
When too much carbohydrate is consumed and not
used for energy over an extended period of time, it is
stored as fat. Building up too much fat will increase
body weight.
Increase dental caries
It is important that teeth are brushed twice a day and
foods high in sugar should be eaten with main meals,
rather than in between snacks to prevent dental
caries.
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Lack of carbohydrate
The short term effects of a lack of carbohydrates are
weight loss and lethargy.
Kwashiorkor and Marasmus are two forms of deficiency
disease which can develop in extreme conditions.
These occur where energy and protein are lacking in
the diet over an extended period of time.
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Protein
Protein is needed for growth, development and repair
of the body.
Excess protein can be broken down and used as a
source of energy.
Protein is made up of different combinations of amino
acids. These are the building blocks of protein.
Amino acids are compounds containing
carbon, hydrogen, oxygen, nitrogen
and, in some cases, sulphur.
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Indispensable or dispensable?
The human body is able to make most amino acids
itself and these are known as non-essential or
dispensable amino acids.
There are some amino acids that cannot be made by
the body.
They are called indispensable amino acids (IAA) or
sometimes essential amino acids.
It is essential that these are provided in the diet as the
body cannot make them.
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Body needs
Adults only need 8 indispensable amino acids for
growth and repair.
Children need to obtain 10 indispensable amino acids.
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Biological value and complementation
It is not just the amount of protein, but the quality or
biological value of the protein that needs to be
considered.
If a protein contains all the indispensable amino acids
it is said to have a high biological value.
If a protein does not contain all the indispensable
amino acids it is said to have a low biological value.
The amino acid that is in the shortest supply in relation
to need is termed the limiting amino acid.
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High and low biological value
High biological value (HBV) proteins include:
meat, fish, eggs, cheese, and milk.
Low biological value (LBV) proteins include:
cereals, pulses, some nuts and vegetables.
In general, animal protein sources have a higher
biological value, than vegetable sources.
Vegetarians and vegans need to eat wisely to ensure
they are getting all the indispensable amino acids.
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Protein complementation
Complementation of low biological value (LBV)
protein sources ensures that all essential amino acids
are consumed.
Amino acids of one protein source can compensate
for the limitations of the other, resulting in a
combination to create a high biological value meal.
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An example of protein complementation
Two foods providing vegetable protein are eaten at a
meal e.g. a cereal (bread) and a pulse (baked
beans).
The amino acids of one protein compensates for the
limitations of the other.
This results in a combination of higher biological value.
© Food – a fact of life 2009
The body’s needs for protein
Babies and children have a high need for protein
because they are growing.
Adolescents need protein for their rapid growth spurt.
Pregnant women need more protein than other
adults because of the growing baby.
Nursing mothers also need more protein for lactation.
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Protein deficiency
Protein deficiency is rare, but there is a condition
called PEM – protein energy malnutrition. This can be
seen in infants with stunted growth or thin arms and
legs, and large distended abdomens.
Marasmus - this condition mainly affects infants
causing them to become thin and weak. The body
adapts to the shortage of energy and nutrients. All
energy stores are depleted as it is used to supply vital
organs.
Kwashiorkor - this condition is known to be the body’s
adaption to shortage of energy and nutrients.
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Fat
Fat performs many functions in the body including:
• providing essential fatty acids;
• providing a concentrated source of energy;
• carrying fat soluble vitamins and is important for
their absorption;
• surrounding and protecting body organs;
• forming an insulating layer keeping the body warm.
Fatty Acid 1
Fat is made up of
fatty acids and glycerol.
Fatty Acid 2
Fatty Acid 3
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Glycerol
Essential fatty acids
The body can make most fatty acids.
Essential fatty acids (EFA) are required for important
functions in the body. These must be provided by the
diet because our bodies cannot make them.
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Sources of saturated and unsaturated fats
• Saturated fat
Meat, coconut oil, palm oil, cakes and biscuits, lard.
• Unsaturated fat
* Mono unsaturated fat
Rapeseed oil, avocado and olive oil.
* Polyunsaturated fat
Oily fish, sunflower oil and pine nuts.
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Over consumption of fat
Eating too much saturated fat has become a problem
in our society.
There are many health problems linked with too much
saturated fat in the diet, e.g. coronary heart disease,
and strokes.
© Food – a fact of life 2009
Review of the learning objectives
• To understand that macronutrients are needed by
the body.
• To know the functions and sources of carbohydrate,
protein and fat.
• To understand the consequences of malnutrition of
carbohydrate, protein and fat.
© Food – a fact of life 2009
For more information visit
www.nutrition.org.uk
www.foodafactoflife.org.uk
© Food – a fact of life 2009