BIOLOGY UNIT 1: NUTRIENTS AND FOOD part I
1. INTRODUCTION
Nutrients are chemical substances that are essential for the body, most of these nutrients are
obtained from food, but the oxygen (O2) is a nutrient that we obtain through the respiratory system.
Food provides us with different biomolecules: inorganic biomolecules (water and minerals) and
organic biomolecules (carbohydrates, lipids, proteins and vitamins), most food contain a mixture of
these biomolecules, all of these are essential nutrients for our cells and for the normal functioning of
our body because our cells need these nutrients for making their own matter and for obtaining energy
(with this energy and matter made in our cells, they can carry out their vital functions). Our body can
obtain energy with a series of chemical reactions using carbohydrates, lipids and proteins. The other
nutrients (water, mineral salts and vitamins) do not provide us with energy. The energy that we
obtain from the nutrients in our food is measured in calories or joules (we normally use kilocalories or
kilojoules because a calorie is a very small unit). We need about 2,000 to 3,000 kilocalories a day (it
depends on your size, age, the exercises you do…). When we buy a packet of food in the
supermarket we can check the kilocalories it contains and the amount of nutrients (carbohydrates,
lipids, proteins…) on the nutritional label. Examples of nutritional labels:
Exercises: 1) Why are nutrients essential for the body?
2) What nutrients provide us with energy?
3) What is your daily energy value?
(See table to the right)
1
2. VARIED AND BALANCED DIET
Every type of food contains different concentration of nutrients for example an orange
is rich in vitamin C and sugars but is poor in proteins, lipids and some vitamins, so if we only
eat oranges we would have a deficiency in proteins, lipids and some vitamins and an excess of
sugars and we should eat some food that provide us with the nutrients that the orange do not
contain. To have a balanced diet (with all the nutrients we need in the right amounts) we need
to eat different types of food (varied diet). In conclusion, to have a balanced diet without an
excess or deficiency in any nutrients, our diet should be varied.
The amount and type of food you eat has a major influence on your health. If you eat a
well-balanced diet, it can reduce your risk of various diseases as well as help you to maintain a
healthy weight. A good balanced diet includes mainly plant-based foods (olive oil, vegetables,
legumes, fruits and cereal grains) and small amounts of animal products (better more fish than
meat). It is important that the food is natural (avoid processed food) and not to eat too much
(only the amounts you need, don’t eat when you are not hungry).
A doctor of the early 16th century called Paracelsus is often referred to as “the father of
toxicology”. He said “the dose makes a poison”, it means that we need a right concentration of
each nutrient because a high dose (excess) or a low dose (deficiency) can be harmful. For
example a lack or deficiency of vitamin D cause weak bones and an excess of sugars can lead
to obesity, diabetes, cardiovascular disease…
In developed countries some common nutritional imbalances are an excess of sugars,
animal proteins and animal lipids, salt, omega-6 fatty acids and a deficiency of plant-based
food, omega-3 fatty acids and fibre. These nutritional imbalances are a major contributor to the
chronic diseases that are so common in developed countries.
Exercise: Why should we have a varied diet?
What should include a
balanced diet?
2
3. INORGANIC BIOMOLECULES (WATER AND MINERALS)
3.1 WATER
Water is the most abundant compound in living things. It composes about 65% of the mass of
the human body (90% of cell cytoplasm, 92% of blood plasma, 97% of tissue fluid and lymph ). Water is known
as the “Universal Solvent”. It dissolves many molecules; this way materials (nutrients and waste)
are transported within living things by water and allows chemical reactions to take place in living
beings. Water is a good absorber of heat energy. It absorbs heat slowly and releases heat slowly. This
allows the tissues of living things to maintain a constant temperature. We need about 3 litres of water
a day, of these, one and a half litres comes from food and the rest we must drink.
Exercises: 1) What are the three functions of water?
2) What would happen if water were unable to dissolve most organic substances?
3.2 MINERALS OR MINERAL SALTS (SALES MINERALES)
Mineral nutrients are inorganic salts that contain elements essential for our body functions
which we only need in small quantities in comparison to proteins, carbohydrates and lipids. They do
not provide us with energy. Examples of mineral salts are sodium (Na), potassium (K), calcium (Ca),
iron (Fe)…We obtain most minerals from the food we eat and some from the water we drink. They
have different functions in the body for example calcium builds and gives strength and density to
hard parts (teeth and bone), our red blood cells contain iron that binds to oxygen so that it can be
transported, most minerals such as sodium, chlorine and potassium are soluble in the body’s liquids
and they help to maintain the correct water balance in the cell (water goes where the salt
concentration is higher: when the salt concentration is higher in the interior of the cell than the external environment,
water enters the cell and when the salt concentration is lower in the interior of the cell than the external environment,
water leaves the cell). The most common mineral salt is sodium chloride (NaCl) of table salt. There is an
excess of NaCl in processed food and you should not eat more than 3g a day of NaCl (may cause
problems in the excretory system and increase blood pressure.
Exercise: There is a
disease
called
osteoporosis
(weakening of the bones). What
is missing in the bones?
3
4. ORGANIC BIOMOLECULES (CARBOHYDRATES, LIPIDS AND PROTEINS)
4.1 VITAMINS (VITAMINAS)
These are different chemical substances that are needed in very small quantities for the
correct functioning of the body. They are not made by the body (but vitamin D can be produced in
skin exposed to UV light) so they have to be ingested in nutrition. There are 2 general types of
vitamins:
- Water-soluble vitamins: These are vitamins that are soluble in water. Examples: vitamin C (is
needed to make and maintain connective tissue), vitamin B1, vitamin B2 and vitamin B3 (B1, B2 and
B3 are needed to obtain energy from nutrients).
- Fat-soluble vitamins: These are vitamins that are not soluble in water (These vitamins are soluble in
fat). Examples: vitamin A (helps with sight) and vitamin D (is needed for bone formation).
Vitamins are destroyed easily by heat (light and oxygen can destroy them too so it is
important to eat fresh food soon after buying it). To obtain the vitamins we need everyday it is
important to eat raw food everyday such as fruits and salads (tomatoes, lettuce, onion, carrots…).
Exercise: Why should we eat raw food everyday?
4
4.2 PROTEINS (PROTEÍNAS)
They are the most important structural molecules: your hair, muscles, bones contain structural
proteins. Some proteins called enzymes are necessary to produce chemical reactions in the body.
Other proteins have specific functions like contracting (muscle proteins) and transporting oxygen
(blood protein. Proteins contain 4 calories per-gram, although, their function is not to obtain energy,
when our body needs energy it uses mainly carbohydrates, lipids are used to obtain energy mainly
when the amount of carbohydrates decreases and proteins are used to obtain energy in case of an
emergency (for example: if you are fasting). Our kilocaloric intake should be made up of no more
than 10% of proteins.
All proteins are made up of single molecules called amino acids,
there are twenty different types of amino acids forming all the proteins,
twelve of these do not need to be obtained from food because they can be
made by the body from other amino acids. The other eight amino acids
are called essential amino acids because they can not be made by the
body, and must be obtained from food.
Protein-rich food are legumes (legumbres: lentejas (lentils),
habichuelas (beans), garbanzos (chickpeas)…), meat, fish and eggs. In
developed countries we eat an excess of meat and proteins.
Meat also contains a lot of fat related to obesity. It is better to obtain most of the proteins you need
from plant-based food and from fish than from meat (meat also contains toxics: antibiotics, hormones, etc.).
4.3 LIPIDS (LÍPIDOS)
They are very diverse substances that are insoluble in water. Lipids contain 9 kcal/g. It is
recommended that 25-30% of the calories in our diet should come from lipids. The most known
lipids are cholesterol and fats. Cholesterol has a structural function because it is present in animal cell
membranes. Fats are the most abundant lipids, they have an energetic function. We accumulate fats
in our body as an energy store. We have accumulation of fat under the skin that isolates the body
from the cold. In general, men accumulate fat mainly around the waist, and women tend to
accumulate fat in the lower body (buttocks, thighs, hips). An excess of fat in our body causes obesity.
An excess of carbohydrates or proteins can not be stored, so they are made into fats.
Fats contain chemical substances called fatty acids, according to their chemical composition,
fatty acids are classified as saturated fatty acids and unsaturated fatty acids. Fats that contain mainly
saturated fatty acids are called saturated fats, these are solid and usually obtained from animals
(saturated fats are abundant in eggs, meat, butter…) and fats that contain mainly unsaturated fatty
5
acids are called unsaturated fats, these typically come from vegetables and they are liquid and are
also called oils (unsaturated fats are abundant in olive oil, sunflower oil…). Two types of unsaturated
fatty acids called omega-6 and omega-3 are essential fatty acids because they can not be made by
the body and must be obtained from food.
Meat contains a lot of cholesterol and saturated fats. Our meat intake must be reduced to
avoid the excess of protein and animal lipids that typically occurs in developed countries. This excess
is linked or related to many chronic diseases in developed countries such as cardiovascular diseases.
Exercise: What are the differences between saturated and unsaturated fats?
4.4 CARBOHYDRATES (GLÚCIDOS O HIDRATOS DE CARBONO)
They are the most important source of energy for your body. Carbohydrates contain 4 calories
per gram. There are two types: simple carbohydrates (sugars) or complex carbohydrates, depending
on their chemical structure:
 Simple carbohydrates are small biomolecules, they are also called sugars because they
are sweet. The most important one is glucose (glucosa) that is the blood sugar and the main source of
energy for our cells. Other sugars are fructose (glucose and fructose are present in fruits), lactose
(present in milk) and sucrose (sacarosa) that is the sugar that we buy in the supermarket and the main
sugar added during food processing. Sodas (soft drinks such as
cokes), sweets (candy, cakes) and industrial food such as
biscuits, muffins… contain large amounts of simple
carbohydrates, mainly sucrose, an excess of simple
carbohydrates leads to obesity (see insulin and obesity) and
chronic diseases in developed countries such as diabetes,
cardiovascular diseases, cancer...
Exercise: See the coke
ingredients and the nutrition
facts, the only nutrient that
gives calories are simple
carbohydrates; it does not
contain proteins, lipids or
vitamins. What is your body
going to do with the excess of
sugar?
6
 Complex carbohydrates are made up of many glucose molecules that are linked together,
they are not sweet. The most important one is starch (almidón) because it is the most common
nutrient in human diets. It is recommended that about 60% of our kilocaloric intake must be complex
carbohydrates (starch). We do not really need any sugars from our diet because we obtain glucose for
our cells from the digestion of starch (starch is made up of glucoses and your digestive system
digests carbohydrates into glucose). Starch is produced by most green plants as an energy store
(glucose reserve). Starch is contained in large amounts in food such as potatoes, cereal grains (wheat,
corn, rice…) and legumes. Bread, pasta (bread and pasta are made up of wheat or another cereal), potatoes and
rice are the most common foods in a human diet and the most abundant nutrient in all of these foods
is starch.
Another complex carbohydrate is glycogen (glucógeno). This is a glucose reserve for
animals. Glycogen is stored in the muscles and liver.
Another complex carbohydrate is cellulose. It has a structural function in plants: it forms
plant cell walls. Paper, cardboard, wood, cotton and the fibre in our diet are made up of cellulose.
Fibre can not be digested in our digestive system so it does not provide us with energy (herbivores can
digest fibre because they have, in their digestive system, microorganisms that are capable of digesting it) but is very
important for our health (see fibre and health). Many of the complex carbohydrates are good sources
of fibre providing that they have not been refined (see whole grains versus refined grains).
Exercise: Complete the table:
Nutrient
Kcal/g
% daily Kcal
recommended
Examples of molecules
Food rich in this nutrient
Carbohydrates
Proteins
Lipids
7