Unit 2: Food and nutrition                                                1   2   3   4   5

1. Foods and nutrients

Nutrition is the joint of processes that allow living beings obtain the matter and the energy necessary to stay alive.

Matter is used to build and to renew our biological structures and energy to carry out the vital functions. Nutrition is an involuntary and unconscious process in which act different organs and organs systems.

Nutrients are the substances contained into foods which are essential for life.

Feeding is the process by which humans obtain food from the environment. Unlike nutrition, feeding is a voluntary and conscious act.

Food provides us with the nutrients necessary for our bodies to grow and carry out vital functions. These nutrients include biomolecules (sugars, lipids, proteins, vitamins) as well as minerals and water.

a) Water

     Water is the most abundant molecule in our bodies (it makes up about 65%

     of our body mass).

     It acts as:

          - a solvent for most of the other nutrients, which is vital for the body

            to carry out metabolism.

- a carrier for substances between different parts of the body.

- a regulator of body temperature.

     We have water from food and as drinking water. We need to consume

     2 litres of water a day.

b) Mineral salts

     These are small inorganic substances with variable composition (e.g. salt)

     that have different functions in our body:

          - In solid state they are structural, making up an important part

            of our bones and teeth.

- In dissolution they are regulatory and allow our organs to function

   correctly and intervene in the regulation of cell metabolism.

     Mineral salts are present in variable quantities in all our food, especially

     in fruit and vegetables, and some of them are in the water we drink.

c) Glucids (sugars or carbohydrates)

     They are molecules composed by carbon (C), hydrogen (H) and oxygen (O).

     These are energetic and structural substances found in many foods

     that we eat daily, such as bread, cereals, vegetables, pasta and potatoes.

     They have to be the 55% of our daily ingestion.

     There are two groups:  

- Simple sugars have a sweet flavour and are crystalline and soluble in water.

        - Monosaccharides. They are the simplest ones. These are used

          directly by our cells.      

             E.g. glucose and fructose present in honey and fruit.

        - Disaccharides. They are formed by two monosaccharides

          joined together.

          E.g. sucrose present in sugar and lactose present in milk.

- Complex sugars (Polysaccharides) are neither sweet nor

   crystalline and they are not soluble in water, although they are 

   made upof many simple sugar molecules joined together.

   From the nutritional point of view, the most important ones are:

         - Starch. It is made up of glucose molecules. It is a source of energy.

         - Cellulose, which makes up vegetable fibre. It forms the plant

            cellular wall. Humans are unable to digest it.

d) Lipids

     Their general composition is carbon (C), hydrogen (H), oxygen(O) and

     sometimes, sulphur (S) and phosphor (P).

     These are a variety of very different substances which are insoluble

     in water and have an oily appearance.

     There are different groups within lipids:

            - Simple lipids or fats are high -energy -giving molecules which,

            because of their chemical composition, are classified into:

                                   - Saturated fats (lards and butter): They are solids and come from

                animals.

              - Unsaturated fats (oils): They are almost always from plants

                and usually liquids.

         - Complex lipids, for example:

- Phospholipids and cholesterol that make upthe membranes

  of cells and organelles.

- Some vitamins and hormones that have regulatory function.

     They must be the 30% of our daily diet.

e) Proteins

     The chemical components of proteins are carbon (C), hydrogen (H), oxygen (O)

     and nitrogen (N).

     They are formed by single molecules, called amino acids, joining together

     forming long chains. All proteins are made up of the same types of amino acids;

     what varies is the proportion and the order in which they combine.

     There are twenty different amino acids. Twelve of these are manufactured

     by the body itself, so these are found in our bodies even if they

     are not in our diet. The other eight amino acids, called essential amino acids,

     cannot be made by our body and must be obtained from the food we eat.

     Many animal products (meat, fish, eggs and milk) and some vegetables

     (pulses) are rich in protein.

     The main functions of proteins are structural and regulatory (some

     hormones and vitamins, and antibodies, enzymes, etc.)

     The daily amount of protein has to be the 15% of the diet.

           - Hydrosoluble vitamins: These are soluble in water, but insoluble in lipids.

       They don't accumulate in the body.

       Examples of these are: vitamins B₁, B₂, B₁₂ and C.

1.1. What are the differences between feeding and nutrition?

1.2. Indicate what of the following substances nutrients are and

        what food are: orange, steak, chocolate, water, spinach, salt,

      ham, oxygen, tomato, anchovy, amino acids, olive oil.

1.3. What the difference is between:

       a. Simple glucids – Complex glucids

       b. Saturated fats – Unsaturated fats

       c. Hydrosoluble vitamins – Liposoluble vitamins

       d. Essential amino acids – Non-essential amino acids

1.4. Explain why to drink water is so important.

1.5. Indicate what quantity of each nutrient we need daily.