Download unit 2: food and nutrition

UNIT 2: FOOD AND NUTRITION.Food is one part of nutrition.
It gives us materials to obtain the matter and the energy that we need. It provides us
with the nutrients necessary for our bodies to grow and carry out vital functions.
Nutrients contain biomolecules.
Classification of nutrients.There are two groups of nutrients:
- Inorganic biomolecules: water and minerals
- Organic biomolecules: carbohydrates, lipids, proteins and vitamins.
Sugar or carbohydrates.They give us the energy that our cells need. We can find sugar in a lot of foods like
bread, cereal, potatoes, pasta and vegetables.
There are two groups of carbohydrates:
1. Simple sugars: they have a sweet flavour, are crystalline and are soluble in
water.
They include:
- Monosaccharides: they are the unit of all sugars, and they give immediate
energy to cells. The most important monosaccharides are glucose (It is the fuel
to cells) and fructose (It is present in fruits and in honey).
- Disaccharides: they are formed by two monosaccharides joined together. They
give us energy too. The most important disaccharides are sucrose, present in
sugar, and lactose, present in milk.
2. Complex sugars or polysaccharides: they are neither sweet nor crystalline, but
they are made up of many simple sugar molecules joined together. So, they must
be broken down for our bodies to use them to obtain energy.
The most important are:
- Starch: principal polysaccharide in our diet. It is of vegetable origin, it is made
up of many glucose molecules and it is the energetic store for plants.
- Glycogen: It is similar to starch but of animal origin.
- Cellulose: It makes up vegetable fibre. It can not be used as a source of energy
because it does no provide any calories.
Lipids or fats.Lipids are a variety of very different substances which are insoluble in water and
soluble in organic solvent and have an oily appearance. They are formed by fatty acid.
Foods rich in lipids are: oil, butter, cream, bacon, etc.
The main groups of lipids are:
- Fats: are high-energy-giving molecules, which because of their chemical
composition, are classified into:
. Saturated fats, which are usually from animals.
.Unsaturated fats, which are from vegetables and are usually liquids, which is
why they are called oils.
The main functions of fats are:
. They store energy in the adipose tissue.
. They are a thermal insulator because they help our bodies avoid losing heat.
- The phospholipids form the membrane of cells together with proteins.
-
Wax: they cover some structures like fruits, feather, leaves, etc, and they
waterproof them.
Regulatory lipids: Includes some vitamins and hormones.
Proteins.They are macromolecules and are the most important organic component in our body.
They are the most important structural molecules.
Proteins are formed by simple molecules called amino-acids joined together. All
proteins are made up of the same types of amino-acids, what varies is the proportion
and the order in which they combine.
To make proteins, the body uses amino-acids which can be obtained from protein-rich
foods like fish, meat, milk, egg, etc.
There are twenty amino-acids in the body. Twelve of these are manufactured by the
body from other amino-acids, so these are found in our bodies even if they are not in
our diet. The other eight amino-acids, called essential amino-acids, can not be made by
our body and must be obtained from the food we eat.
Proteins have the following functions:
- They make a lot of structures like muscles, membranes of cells, hair, nails, etc.
- They transport substances in our body like haemoglobin.
- They do muscular contraction.
- They defend our body against infections: antibodies.
- They send messages: hormones.
- They regulate all the transformations that happen in our body: the enzymes
Vitamins.The most important characteristic of vitamins are:
- They are substances of different chemical compositions, which are vital for the
correct functioning of the body.
- Foods rich in vitamins are fruits and vegetables.
- They have regulator functions, which are different for each vitamin.
- They are needed in very small quantities.
- They are destroyed easily by heat and by time, light and oxygen.
- There are two main groups of vitamins:
. Hydrosoluble vitamins: they are soluble in water but insoluble in lipids. They
don’t accumulate in the body because they can be eliminated through the urine.
Examples of these vitamins are vitamin B1, B2, B12, C.
. Liposoluble vitamins: they are soluble in lipids but insoluble in water. They
accumulate in the liver or in fatty areas of the body, which act as a store of these
vitamins. Examples of these are vitamins A, D, E and K.
- If we have less vitamins than we need, different disorders and illnesses like
scurvy or rickets can develop.
- If we have more liposoluble vitamins than we need, they can build up in fatty
areas of the body and in the liver and can cause damage.
Minerals.- They are inorganic substances that have different functions in our body.
- Some have structural functions, making up important part of our bones and
teeth.
-
Others have regulator functions: they allow our organs to function correctly and
play a part in the regulation of cell metabolism.
Foods rich in minerals are fruits, vegetables, milk, and the water we drink (It has
minerals dissolved in it).
Water.Water is a very important component for living things, because:
- Water is the most abundant molecule in our body (it makes up about 63% of our
body mass).
- A person can survive without water a short time: If we lose 10% of our body’s
water we die.
For these reasons living things have to equilibrate losses and profit in water.
We have profit from drinking water, from food and from metabolic water. And with
urine, sweat, faeces and breathing we lose water.
We need to consume about 2 litres of water per day.
The functions of water are:
- To transport different substances in our body.
- It is the place where the metabolic reactions in the cells happen.
- It is used to regulate temperature.
Nutritional need.We need food to satisfy three types of functions: energetic, structural and regulatory.
1) Energetic function: Food gives energy to maintain the activity of all our cells,
tissues and organs, and to do physical activity.
We obtain the energy we need from energy giving nutrients: sugars and fats.
We obtain the energy by a process called cell respiration that takes place in the
mitochondria. It is a process that needs oxygen.
Different nutrients produce different energy:
. One gram of fat: 9 kcals
. One gram of sugars: about 4 kcals
. One gram of protein: about 4 kcals.
Protein can give energy, but our body only uses proteins in special situations,
like:
. In a long fasting, when sugars and fats are lacking.
. When we eat only proteins.
In normal situations proteins are structural functions.
Our body needs a minimum amount of energy even when we are resting. This is
called the basal metabolic rate, and it is the energy required to keep our vital
functions going: breathing, blood flow, etc. The value of the basal metabolic
rates is expressed in kilocalories per day and it is different for different people. It
depends on body mass, size, age and sex.
2) Structural function:
Food also provides the body with essential substances to build and repair
biological structures.
The most important structural nutrients are proteins, but other are:
. Some lipids (phospholipids) that build cell membranes.
. Some minerals that build bones.
3) Regulatory function:
They are nutrients like vitamins and some minerals that ensure that metabolic
reactions happen effectively. An important group of these nutrients are the
enzymes, a group of proteins.
Diets.The quantity and type of food a person consumes daily is called food intake.
Characteristics:
- A diet is not universal. Each person has eat a different diet. It depends on age,
sex, and activity.
- A diet has to be correctly distributed in time. (The most correctly is to do four or
five meals a day).
- For a diet to be healthy it also needs to be balanced. It must have all the
necessary energy, structural and functional nutrients, in the right quantities.
To have a balanced diet, you should follow the following advice:
. Eat a variety of different foods.
. Eat several times a day.
. Eat fresh vegetables.
. Avoid precooked and refined foods.
. Include unsaturated fats.
. Reduce your intake of foods rich in saturated fats and cholesterol.
. Consume fibre-rich foods every day.
- A food wheel is a diagram which shows us the composition of a balanced diet.
Different types of food are organised into segments according to the nutrients
they provide and their functions in the body.
There are seven groups of foods based on the types of nutrients they contain.
Another form to represent a balanced diet is the food pyramid.
One example of a balanced diet is the Mediterranean diet. It refers to traditional
food from countries in Southern Europe, like Spain. It is considered to be one of
the most balanced and healthy diets.
In a Mediterranean diet the basic types of food are olive oil, cereals, vegetables,
fish, green vegetables and fruits.
-
Special diets.People who have different disorders and illnesses need to follow special diets,
different from a balanced diet.
Some special diets are:
Low or high calorie diets.
Low cholesterol diets.
High fibre diets.
Low fibre diets.
Inadequate diets.An inadequate diet can cause changes in the body and illnesses which can be serious
or even fatal. Examples:
- Malnutrition: This occurs when the quantity of food eaten is not enough to
satisfy the body’s nutritional needs. This includes the wasting or marasmus, and
kwashiorkor.
- Incorrect nutrition: This refers to eating certain types of food which are not good
for us .It includes:
. Vitamin deficiency
. Obesity
. Cholesterol
Dietary habits.For historical, cultural, social and even religious reasons, dietary habits are different all
over the world.
- In many developed countries, nutritional imbalance is common. Illnesses linked
to nutrition are characterised as follows:
.If there is a very high calorie intake which can lead to obesity and certain types
of diabetes.
. Food rich in cholesterol and saturated fat increases the risk of circulatory
problems.
. An excess of refined foods with little waste can cause problems like
constipation.
. Too much protein- rich food.
. Eating processed foods can lead to an excess of additives, which can damage
your health.
- In developing countries the diet is not always adequate, but for different reasons:
. Diets tend to be low in calories so, at times, the body does not get enough
energy.
Diets are often monotonous and because of the lack of variety of food, the body
lacks vital vitamins.
. Protein intake tends to be poor.
. Sanitary conditions during the handling and preserving of food are often poor.
This can lead infectious diseases and food poisoning.
Genetically modified food.They are foods obtained from genetically modified living things by introducing genes
from one organism into another type in order to change the genes and improve the food
it produces.
These types of food have advantages and disadvantages.