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NUTRITION IN ANIMALS
USES OF FOOD
Food is needed for various life activities. The food eaten may be used by the body
for the following activities.
It provides raw material for growth and development
It is needed to yield energy during respiration for various activities like
movement, thinking, breathing, pumping of heart
It may be needed to enable the body to use the raw materials and to
produce energy effectively.
FOOD
It can be defined as any solid or liquid substance which, when taken by the body,
provides it with the necessary materials to enable it to grow, to replace worn out and
damaged parts, and to function normally.
NUTRIENTS
The molecules in the food used by the body to function properly or stay healthy are called
nutrients
Nutrition
The study of nutrients and their relationships with food and living things is called
nutrition.
Diet
Diets means a food that a person eats every day
Balanced diet
Diet that provides the correct amount of nutrients for the needs of an individual.
Malnutrition
Malnutrition means an incorrect or unbalanced intake of nutrients. It may be under
nutrition or over nutrition.
Under nutrition
An insufficient total intake of nutrients is termed as under nutrition.
COMPONENTS OF FOOD
The food contains following important components.
Proteins
Fats
Carbohydrates
Vitamins
Minerals
Dietary fibers
Water
Carbohydrates
Carbohydrates are compounds of “C, H, and O”. Their general formula is
CnH2nOn. They are called hydrated carbons as the proportion of hydrogen and oxygen in
the carbohydrates is same as that of water.
Sources
The principle sources of carbohydrates are the process of photosynthesis in green
plants. It combines atmospheric carbondioxide and water from the soil in their green parts
to make glucose. In this process the light energy is converted to chemical energy. The
glucose synthesized is used for its own metabolic activities, any left glucose is converted
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to starch and is stored in various parts of the plants i.e., grains, fruits, stem, roots or
leaves.
Some principle sources of carbohydrates include
Cereals e.g. wheat, rice, oat barley
Fruits e.g. banana, apple, mangoes
Vegetable e.g. cauliflower, turnip etc.
Classification of carbohydrates
Principally carbohydrates are of three kinds, i.e. monosaccarides, oligosaccharides
and polysaccharide
Monosaccharides
These are simple sugars. They are the basic units that built the other
carbohydrates. They are soluble in water and sweet in taste. They cannot be hydrolysed
into further simple sugars.
Some common monosaccharides
Fructose
It is also called fruit sugar. It is found in fruits, plant juices and honey. The
chemical formula for fructose is same as that for glucose i.e. C6H12O6.
Glucose
It is also called as grape sugar. It is found in ripe fruits and some vegetables e.g.
onions, beetroot. It is the product of digestion of carbohydrates in the body and taken up
into the blood to be supplied to the respiring cells and tissues. It is a six-carbon sugar.
The glucose units may be condensed together to form various complex carbohydrates
like, starch, cellulose and glycogen.
Galactose
It is another simple sugar that makes part of milk sugar, i.e. lactose.
Disaccharides
Disaccharides consist of two simple sugars joined together. Two monosaccharides
usually hexoses are linked together by a glycosidic linkage. They are linked together by a
process known as condensation.
Condensation
Hydrolysis
Disaccharides are soluble in water and lesser sweet than monosaccharides. Some
examples of disaccharides are
Sucrose
Glucose + fructose --------- sucrose
Lactose
Glucose + galactose -------- lactose
Maltose
Glucose + glucose ========= Maltose
Polysaccharides
These are formed from a varying number of monosaccharides units. The repeated
glycosidic bonding between many simple sugar units make polysaccharides. They are
usually insoluble in cold water and are tasteless. They function chiefly as food and
energy stores and as structural materials. They are convenient storage molecule for
several reasons.
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Their larger size makes them more or less insoluble in water, so they do not exert osmotic
or chemical influence in the cell.
Due to longer chains of simple sugar units joined together, they can fold into compact
shapes.
They can easily be hydrolysed to simple sugars, when required.
Starch
Starch is formed from many glucose units joined together by glycosidic linkages.
It is a major fuel store in the plants, but is absent in animals. It can be seen in a plant cell
under an ordinary microscope in the form of starch granules. And can be confirmed with
iodine test, where it gives blue-black color with iodine.
During digestion that starts in the mouth, starch is broken down to maltose and
then into glucose in the intestine, which is absorbed into blood.
Cellulose
Cellulose is formed by plants from glucose units joined together in such a way
that a strong, structural material is produced. It is the most abundant organic compound
present on the earth. It is potentially source of glucose but naturally cannot be digested in
the human body. However some herbivores have cellulase-producing bacteria in their
intestines and can digest cellulose.
FATS
Fats are compounds of fatty acids and glycerols. They are insoluble in water and
soluble in organic solvents like either, chloroform and benzene. They consist of C, H and
O (Carbon, Hydrogen and Oxygen).
3(Fatty acids) + 1(glycerol) ------- 1 Fat
Fatty acids
Fatty acids are hydrocarbon chains with an acidic group at one end (-OOH). Most
of the naturally occurring fatty acids have an even number of carbon atoms that varies
between 14 and 22. They are of two kinds.
Unsaturated fatty acids
Saturated fatty acids
Unsaturated fatty acids
Hydrocarbon chain of the unsaturated fatty acids contains one or more double
bonds. They are present in oils. They are liquid at room temperature. E.g. Oleic acid, a
chief constituent of Olive oil.
Saturated fatty acids
Fatty acids and fats lacking double bonds are called saturated. Saturated fatty
acids are usually solid at room temperature and are found in fats. Palmitic acid for
example is a saturated fatty acid, solid at room temperature.
Alcohols
The most common alcohol in fats is glycerol. The formula for
glycerol is given below.
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Formation of fats
As in the above formula, glycerol has three hydroxyl groups (-OH). These
hydroxyl groups under go condensation reactions with three fatty acids as shown below.
Functions of fats
Fats are an efficient source and storage of energy. It provides double of the energy
produced from the same amount of carbohydrates and proteins.
It acts as an insulating layer under the skin. It prevents excessive heat loss from the body.
They are source of fat soluble vitamins like vitamin A, Vit.K, Vit.E and Vit.D
They are an important compound of cell membranes.
Surrounds and protects certain vital organs, e.g. kidneys
Provide texture and flavour in food and help to make it palatable
Foods containing fats provide feeling of fullness (satiety) after a meal, as fat digestion is
slow.
It helps to reduce water loss from the skin. The oily secretions from the sebaceous glands
spread on the surface of skin from water loss.
PROTEINS
Proteins are compounds of C, H, O and N. sulpher and phosphorous may also be
present in some. Proteins are made up of smaller, basic units called amino acids.
Amino acids
Amino acids consist of an amino group (-NH2) and an acid group
(_OOH)
attached with the centra
l ∞- carbon. The central carbon also bears a side chain of
hydrocarbons denoted by R. different amino acids have differences
in this R group attached. The general formula for amino acids is
given below.
There are at least 22 amino acids known, naturally occurring in plant and animal
proteins. Some of them cannot be synthesized in the human body, and should be taken in
diet, so they are called essential amino acids.
Proteins containing these essential amino acids may be called first class proteins,
high biological value or complete proteins. Meat, cheese, fish, milk and eggs provide first
class proteins.
Proteins that lack one or more essential amino acids are called second class or low
biological value proteins. The followings proteins provide low biological value proteins.
Cereals e.g. wheat, rice, oats
Pulses, e.g. peas, beans, lentils
Amino acids are linked together by peptide bonds. A peptide bond is a linkage between
nitrogen of amino group
of one amino acid and
carbon of carboxylic
group of another amino
acid. This process of
linking of two or more
amino acids in a chain is called condensation.
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Functions of proteins
Our bodies are made up of millions of cells, which are constantly being replaced and
require. New protoplasm is essential for the formation of new cells. So new protoplasm
must be produced. The proteins are needed for
The synthesis of protoplasm, i.e. for growth and repair of worn-out body cells.
The synthesis of enzymes and some hormones.
The formation of antibodies to combat diseases.
Energy producing.
Some examples of proteins and their functions
PROTEIN FUNCTION
Hemoglobin transport of oxygen
Keratinformation of nails and hairs
Myosin
formation of muscles
Collagen
formation of bones and cartilage
Insulin
VITAMINS
Vitamins are group of chemical substances required in small amounts. They are
required to regulate the maintenance and growth of the body, and to control metabolic
reactions in cells. Vitamins cannot be synthesized in human body so they should be taken
in diet. Lack of vitamins causes deficiency diseases. Some common characteristics of
vitamin are as follows.
They are not used as a source of energy.
They do not make part of body structure.
They are essential for normal health and are needed in small amounts.
They usually work in association with enzymes.
At least fifteen different vitamins have been identified and can be classified into two
groups according to the substances in which they dissolve.
Fat soluble vitamins; A, B, E and K.
Water soluble vitamins; vitamin C and the vitamin B-complex.
Vitamin A
(Retinol)
Functions
It is required to make a substance called visual purple, which is formed in the
retina of the eye to enable it to see in dim light. For the normal development of the
epithelial tissue and the mucus membranes in the throat and the digestive, bronchial and
excretory system, Vitamin A is needed. It also helps in the maintenance and development
of skin. Children need it in sufficient amounts for their normal growth, particularly the
bone and teeth formation.
Sources
Animal sources
Being fat soluble it is found in fatty foods or products i.e. milk, cheese, eggs
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(yolk), butter oily fish e.g. herring, sardine, Liver, kidneys, and cod liver oil.
Plant sources
In plant foods it is present in the form of carotene that may be later converted into
retinal in the human body. The plant foods like carrots, spinach, watercress, apricot,
parsley, cabbage, tomatoes and plumes.
Dietary guide for Vit.A
As vitamin A is fat soluble, it is stored in the body. So it is not necessary to be taken in
the daily diet. The excess of vitamin A in the body may be poisonous. It seriously affects
the development of skin and joints. In the growing ages it is very essential to be taken in
the proper amounts. In the pregnant women if they eat liver for vit. A supplies, it may
seriously affect the developing babies. So they should avoid liver, instead they should eat
sufficient fruits and vegetable that provide carotene. It does not lead to damage and
defects in unborn babies.
The people with their gall bladder removed are advised not to take fats in their
diet. They lack vit. A in their diets. The others, who cannot adjust fats, should be given
vit. A through injections.
Deficiency of vitamin A
Deficiency of vit. A leads to night blindness. In sever cases it causes total blindness.
The skin and mucus membranes become dry and infected, and resistance to diseases is
reduced.
Growth of children is retarded.
Vitamin C
(Ascorbic acid)
Functions
It helps in the formation of connective tissue. It also assists the absorption of
mineral iron from the small intestine after digestion. It is needed for the development of
bones and teeth.
Sources
Vitamin C is a water soluble substance. It is mainly found in fresh fruits and
vegetables, which include blackcurrants, green pepper, kiwi fruits, oranges, grape fruits,
lemon, strawberries, cabbage, spinach, Brussels sprout, broccoli and potatoes.
Dietary guide for vitamin C
Although it is a water- soluble vitamin, it is stored in the body in the liver, adrenal
glands and through out the body fluids and tissues. A healthy man has up to 1.5 grams of
ascorbic acid stored in this way. Only 45 mg of it are used daily. A daily supply of
vitamin C is needed to keep the store ‘topped up’. Cooking oxidizes vit. C C and being
water soluble it may be lost during washing and cooking foods. So the fresh food should
be used to avoid lack of vit. C
Deficiency of vit. C
The severe deficiency of it causes scurvy. The symptoms of scurvy include
Bleeding of gums
Loosening of teeth
Impaired wound healing
Anemia
Heart failure
Vitamin D
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It is required for proper development of bones and teeth. It also regulates the absorption
of calcium from the gut.
Sources
It is a fat soluble vitamin and is found in good supply in liver, cod-liver oil. It is
also found in milk and dairy products. An important source of vitamin. D is a precursor in
the skin that is converted to vit. D by U.V light when exposed to sunlight.
Dietary guide for vit. D
If is a fat soluble and can be stored in the body. Most people make enough vitamin D
from the action of sunlight on their skin. So it is not suggested to give addition vitamin D
for school going children, adolescent and adults. Usually deficiency of vitamin does not
occur, however in babies in cold winters when they are packed most of the time and their
skin is not exposed to sun light, and the house bound people or those, whose cover their
body as part of religious custom, are likely to be deficient.
Excess of Vitamin D in the diet can be dangerous. It assists absorption of more
calcium into the blood, if in excess may be deposited in the lungs or kidneys.
Deficiency
Deficiency of vitamin D causes weakening of the bones and bowlegs in children called
rickets. In elderly people softening of bones occurs. So they become liable to fractures
easily. This is called osteomalacia.
MINERALS
Human body consists of at least 20 different elements. Some of them i.e. C, H, O,
and N make larger proportion in the body and their main sources are carbohydrates, fats
and proteins. Seven of these minerals are needed in only trace amounts for good health,
and these are known as trace elements. They include magnesium, copper, zinc and iodine
Calcium
Functions
It is the part of mineral component of the bones and teeth.
It is needed in addition to other substances to initiate blood clotting
It is needed for muscular contraction and transmission of nerve impulse
It play a part in permeability of cells
Sources
Milk is a good source of calcium. The other sources include cheese, bread, bone
of canned fish and hard water.
Dietary guide for calcium
Adults need about 800 mg calcium each day, children, pregnant and lactating
mothers even need higher amounts of calcium.
Fe (IRON)
Functions
Iron is needed fro the formation of RBCs. It is an important component of hemoglobin. It
is also needed for the formation of hydrogen acceptor system of the cells.
Source
Liver, kidney, corned beef, chocolate are good sources of iron. Eggs, spinach, dried
fruits whole grain cereals also provide iron.
Dietary guide
Adults need about 15mg per day. Its absorption into the blood depends up vitamin c.
Vitamin C increases iron absorption from plant sources. So to ensure iron absorption the
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foods contain iron should be taken along vitamin c. in growing children pregnant and
nursing mother more iron is needed.
Deficiency
It leads to anemia, the deficiency of hemoglobin & shortage of RBC’s in the blood due to
iron deficiency causes iron deficiency anemia.
Energy
Energy is needed when a person is awake for the physical activities and even when a
person is asleep to carry on the vital processes of the body i.e. heart beat, breathing etc.
all energy needed is provided by the food, that is oxidized to release energy in the cells
after it is digested absorbed and carried to the tissues.
Uses of energy in the body
In the human body the energy is used in various forms. The primary source o fall these
forms of energy is the sun light which converted into potential energy in food by a
process called photosynthesis the food after it is eaten is digested, absorbed and
transparent to the cells or tissues where it is oxidized to produce energy. The energy
released may be used to maintain the body temperature or to make ATP. ATP is used to
perform various activities in the body. Ti is converted to mechanical energy to bring
about muscular movement or may be transformed into electrical energy for the
transmission of nerve impulse.
Energy Sources
Various kinds of foods are initially the source energy for the body. The carbohydrates in
our diet are the cheapest and readily available source of energy, proteins that should be an
essential part of our diet are usually expensive and produce almost the same energy as
provided by carbohydrates, fats are rich source of energy, they provide double of the
energy released from carbohydrates or proteins.
Energy Release in the body
Oxidation of food releases energy. And will be discussed separately.
Measurement of energy
The amount of energy that can be obtained from food is measured in calories or joules.
1 cal = m4.2 joules the other conversions of these units are
1000 cal = 1 kilo cal and
1000 joules = 1 kilo joules
1 kilo cal = 4.2 kilo joules
Kilo calorie
Amount of heat energy needed to raise the temperature of one kilogram of pure water by
1 degree centigrade
Measurement of energy content of a food provided
In the living cells the energy is released during oxidation. However combustion of food
releases energy in the form of heat. The energy value of any food can be measured based
on an assumption, that the energy released during combustion is equal to the energy
released during oxidation. The energy value is found using a food calorimeter
Procedure
A weighed sample of food is completely burned in an atmosphere of oxygen. The heat
released by this combustion is transferred to a known volume of water, which rises in
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temperature as a result; the energy value of the food can be calculated as follows
Energy value of food in calories per gram = Temperature rise (0C)
Energy values of different foods
The energy values of the organic components of food are given below
Fats 3g kj/g or 9kcal/g
Protein 17 kj/g or 4cal/g
Carbohydrates 16 kg/g or 3.75 kcal/g
Vitamins and dietary fibers are organic components of food but they do not release
energy in the body.
Energy requirement
It requirements of an individual vary from that of the others. The factors that
effect the energy requirement are explained below.
Climate
People living in colder regions tend to lose more heat to the atmosphere so they need
more energy in order to maintain their body temperature. To conserve heat loss thick
insulating layer of fats may be deposited under the skin
Body size
In similar climatic condition, the people of the same sex and age may have different body
sizes and weights.
Age
Young children require more energy for their size than adults as they are growing rapidly
and tend to be very active most of the time. With the increase in age the energy
requirement decrease due to the slowing down of the body metabolism and reduced
physical activity.
Sex
Men have bigger built than the women of the same age, the metabolism is higher in men
so they need more energy
Occupation and physical activity
The amount of energy needed depends upon the basal metabolism and physical activity.
Energy needed = BM + energy needed for physical activity
The physical activity in the adults may be related to their work or occupation
Sedentary office workers, drivers teachers, journalist, doctors, layers, shop workers
energy needed 450 kJ
Moderately active: light industry and assembly plants railway workers, postmen and
women, plumber’s etc. 1500kj
Very active coal miners, steel workers, army recruits, labours (2050kj)
Pregnancy
Pregnant women need extra energy for the growth of the baby, to hold or to carry the
extra burden and the adjustments of the mother’s body to pregnancy.
Balanced diet
A balanced diet contains the right proportion of carbohydrates, protein, fats,
vitamins, minerals, water and roughage to meet the daily requirements of the body
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A balanced diet varies from person to person, the proportion of the nutrients required in
the diet is really affected by the life style, occupation, age, sex and state of the body of a
person, and the food after it is eaten is digested and absorbed. It is oxidized to release
energy and is metabolized for growth and repair of the body. As the energy requirements
and growth state varies from person to person, the balanced diet for various categories
may be discussed as below.
Pregnancy
The developing embryo in the wombs of a mother needs amino acids for building the
proteins of its tissues, calcium for development of skeleton, iron for blood formation and
energy to carry out all these metabolism activities, the developing embryo obtained all
these substances from the blood of mother. So a pregnant woman should increase her
protein, calcium and iron intake. She should also ensure various vitamins in her diet that
are essential for normal development of the embryo.
Lactation
Milk production for feeding the baby is called lactation.
Lactation means the production of breast milk for feeding the baby. The production of
milk depletes protein and minerals from the mother’s body. So she should take extra
amount of proteins and diet containing minerals especially calcium and iron.
Age
The young children require more energy for their active life and growth. So the
food requirements of children in proportion to their body weight are more than adults. In
the children formation of new tissues, blood and development of skeleton demands foods
rich in proteins, iron and calcium. High carbohydrate food should be avoided in children.
Great care should be taken, if vitamin A, D is to be given extra. Their too much amount
may be poisonous however their adequate supply is very essential for normal growth in
children. With the increase in age the growth rate slows down and in old age the people
usually become less active. They lose their teeth and digestion becomes very slow so they
take little food. It may result into lack of many essential amino acids, fatty acids and
minerals and vitamins in their diet. They should be given food that can easily be chewed
and digested and still provide low level of vitamins and minerals.
Malnutrition
Malnutrition means bad feeding. It could include
Eating foods in the wrong proportions, for example very high fat content in the diet.
For an adult the balanced diet on average provides almost 1200 kj of energy. Foods may
be eaten more than it is needed.
Eating too little food than is needed daily.
Over nutrition
If the diet contains more energy than needed by the body for basal metabolism
and physical activities, the excess will be stored as glycogen or fat. However, body can
store a limited amount of glycogen in the body and unlimited amount of fat under skin
and round the vital organs. Its storage above a healthy limit causes obesity and the person
is called obese.
Obesity
Obesity can be defined as a state of individual that has 20% more weight than the
average for some one of its height and overall frame size.
Causes of obesity
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The major factors that result into obesity are
Eating more food
Eating high energy food
Genetic predisposition
Physiological disorders
Physically less active life
Effects of obesity
Obesity can lead to
Cardiovascular diseases
Diseases of the joints
Diabetes
Hernias
Emotional problems
Under nutrition
Under nutrition is not a problem of most developed countries. In the developing
countries like Pakistan, many people have diets, which bear neither adequate nor
balanced. Their diets do not provide enough ener4gy for their metabolism and physical
activity. Some people receive energy just to ‘stay alive’. Food may lack minerals,
vitamins or even essential amino acids or fatty acids in their diets that result into various
deficiency disease4s. Some of them are described below.
Kwashiorkor
The kwashiorkor literally means” the sickness the old baby gets when the new
baby comes”.
Causes of kwashiorkor
As the meaning of kwashiorkor itself explains, its causes can be. The first child is
removed from the breast milk that provides best food for the babies, and switched to
starchy diet that results in protein deficiency.
Signs and symptoms of this disease
The child suffering from kwashiorkor show characteristic appearance.
Hairs
Hairs become white or red. They weaken and fall easily
Moon-faced
Swelling on the lower cheeks gives characteristic moon-faced appearance.
Abdomen
Abdomen swells and enlarges
Skin
The skin turns pale, scaly and rough. Lesions appear and wound healing is also
reduced.
Body size
If the children suffering from kwashiorkor or not given proper treatment, die
before the age of five. Their growth reduces and their muscles become thin.
Treatment
Protein rich diet, vitamin supplement and proper nursing can help to recover from
kwashiorkor.
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