A balanced diet Flashcards
The food that we eat is called our diet. No matter what you like to eat
your dis must include the following five groups of food substances if your body is to work properly and stay healthy - carbohydrates
Carbohydrates
Carbohydrates only make up about 1% of the mass of the human body
but they have a very important role. They are the body’s main ‘fuel’ for supplying cells with energy. Cells release this energy by oxidising a sugar called glucose
Glucose is found naturally in many sweet-tasting foods
such as fruits and vegetables. Other foods contain different sugars
We can get all the sugar we need from natural foods such as fruits and vegetables
and from the digestion of starch. Many processed foods contain large amounts of added sugar. For example
In fact
we get most of the carbohydrate in our diet not from sugars
Starch is only found in plant tissues
but animal cells sometimes contain a very similar carbohydrate called glycogen. This is also a polymer of glucose
As you will see
large carbohydrates such as starch and glycogen have to be broken down into simple sugars during digestion
Another carbohydrate that is a polymer of glucose is cellulose
the material that makes up plant cell walls. Humans are not able to digest cellulose
Lipids
Lipids contain the same three elements as carbohydrates - carbon
hydrogen and oxygen - but the proportion of oxygen in a lipid is much lower than in a carbohydrate. For example
The chemical ‘building blocks’ of lipids are two types of molecule called glycerol and fatty acids. Glycerol is an oily liquid. It is also known as glycerine
and is used in many types of cosmetics. In lipids
These substances have been linked to heart disease
Proteins
Proteins make up about 18% of the mass of the body. This is the second largest percentage after water. All cells contain protein
so we need it for growth and repair of tissues. Many compounds in the body are made from protein
Most foods contain some protein
but certain foods such as meat
However
we don’t need much protein in our diet to stay healthy. Doctors recommend a maximum daily intake of about 70g. In more economically developed countries
Like starch
proteins are also polymers
Minerals
All the foods you have read about so far are made from just five chemical elements: carbon
hydrogen
Some are present in large amounts in the body
for example calcium
Table 4.1 shows just a few of these minerals and the reasons they are needed.If a person doesn’t get enough of a mineral from their diet
they will show the symptoms of a ‘mineral deficiency disease’. For example
Similarly
16-year-olds need about 12 mg of iron in their daily food intake.
If they don’t get this amount
they can’t make enough haemoglobin for their red blood cells . This causes a condition called anaemia.
People who are anaemic become tired and lack energy
because their blood doesn’t carry enough oxygen.
During the early part of the twentieth century
experiments were carried out that identified another class of food substances. When young laboratory rats were fed a diet of pure carbohydrate
Vitamin A is needed to make a light-sensitive chemical in the retina of the eye.. A lack of this vitamin causes night blindness
where the person finds it difficult to see in dim light. Vitamin C is needed to make fibres of a material called connective tissue. This acts as a ‘glue’
Lack of vitamin C causes scurvy
where the mouth and gums become damaged and bleed.
Vitamin B is not a single substance
but a collection of many different substances called the vitamin B group. It includes vitamins B1 (thiamine)
The main vitamins
their role in the body and some foods which are good sources of each
Notice that the amounts of vitamins that we need are very small
but we cannot stay healthy without them.
