Biology REVISION OF Constituents of FOOD Division FOR NDA


It is the material, which is required by all living organisms for the production of energy, growth,
repairing of tissues and regulation of other life process·cs.

Balanced Diet

• Balanced diet is the diet that contains all the essential components required by the body in the optimum
proportions and quantity suitable for maintaining the body in perfect state of health, activity and development.

• Various substances of balanced diet are carbohydrates (60%), proteins (15%), fats (25%), mineral, vitamins,
water, roughage, etc.

• Balanced diet should have carbohydrate, proteins and fats in the ratio of 3/5 : 1/5: 1/5, respectively.
' The components of a ballanced diet are:

1. Water

It is the main component of the body. Human body contains about 65% water and about 70% of this water
is protoplasm.

An average adult needs 5-6 glasses of water daily for the normal functioning of the body. The amount of water

required varies with temperature and humidity of the air and the degree of phy,ical work. Babies/infants under 6 months
are not advised to take water as their kidneys are not that matured to meet the intoxication and sodium present in the

Functions of water are as follows

(i) To control the body temperature.

(ii) To act as an important medium in the excretional activities.

(iii) To regulate almost all biochemical reactions.

2. Carbohydrates

• They are the m<.in energy producers or fuel substance's in our body. They arc stored in plants and animals in the
form of starch, glucose or glycogen.

• These constitute the 1.5'% part of body.

• Carbon, hydrogen and oxygen arc the main components of carbohydrates.

• Carbohydrates ac polymers of smaller units, i.e. glucose.

• Depending on t:1e number of monomers present,

carbohydrats an: of three types

(i) monosaccharides (e.g. glucose, fructose),

(ii) disacc:harides (e.g. sucrose, lactose, maltose),

(iii) oligosaccharides and polysaccharides

(e.g. glycogen, starch, cellulose).

The disaccharide units bound together by glycosidic

(i) Maltose (malt sugar) = Glucose + Glucose

(ii) Lactose (milk sugar) = Glucose + Galactose

(iii) Sucrose (cane sugar) = Glucose + Fructose

• Cotton and paper are pure cellulose.

• Cellulose is a polymer of glucose.

• Animals like cow, buffalo, goat can digest cellulose, but human is devoid of it.

• Starch is converted into maltose in saliva of human beings by an enzyme ptyalin or salivary amylase.

• Its 1.0 g gives 4 kcal energy.

• Living cells receive carbohydrate from blood mostly in the form of glucose.

• Excess of glucose is stored in liver and muscles as glycogen, by the process of glycogenesis.

• When level of blood glucose falls, glycogen in liver is hydrolysed to produce it, i.e. glycogenolysis takes place.

• Excess c2.rbohydrate of food is changed into fat through the process of lipogenesis.

• Cereals (wheat, rice and maize), sugarcane, milk (lactose sugar), fruits, honey (fructose sugar), beet, etc., are the sources of carbohydrates.

• An adult requires 500 g carbohydrates per day.

• This requirement increases in sports persons and lactating mother.

Functions of Carbohydrates

• To supply energy to the body by the oxidation of food.

• To construct the external skeletons of insects and cell wall of plants.

• To form nucleic acids (ribose and deoxyribose sugars).

3. Lipids

• Lipids made of fatty acids and glycerols.

• Lipids are generally of two types; simple, e.g. fat and oil and compound, e.g. lecithin and glycolipid.

• They provide two times more energy (9 kcal!g) than carbohydrates. Oxidation of 1 g fat yields 9.3 kcal

• Fat is the major stored food kept in adipose tissue.

• At 20°C fat is called lipid.

• Stored food is used as fuel, when glucose is not available.

• Lipase enzyme digests fat and breaks it into fatty acids and glycerol.

There arc two types of fatty acids

(i) Saturated These are solid at room temperature.

(ii) Umaturated These are liquid at room temperature.

• Our diet should contain less saturated fats, e.g. butter, ghee hydrogenated vegetable oils, etc.

• Excess of saturated fats in diet may lead to heart attack as they increase blood cholesterol. This disease is known as hypercholesterolemia.

• The unsaturated fatty acids should be more in diet as they cannot synthesised in the body itself. These fatty
acids are called <:ssential fatty acids (e.g. linoleic acid, linolenic acid, etc.).

• Excessive intake of fats may cause obesity. Its symptoms are fat accumulation in tissues, high blood pressure,
cardiac disorder and proneness to diabetes. Functions of Lipids

• Stored source of energy.

• Fat functions as a cuskon and shock absorber for eyeballs, gonads, kidney, etc.

• It provides insulation to the animals living in colder

4. Proteins

• The term 'protein' was coined by Mulder in 1838.

• They are made up of carbon, hydrogen, oxygen, nitrogen and sulphur. Thus, these are required for protein
formation in body.

• They play a vital role in growth, development and repair of the body. All enzymes are protins except ribozymes.

• Tney are digested in alimentary canal by the action of pepsin and trypsin enzymes.

• They are the building block substances of body.

• Proteins are polymers of amino acids.

Amino acids are of two types

(i) Essential cannot be synthesised in the body and must be taken in diet, e.g. lysine, methionine, valine,
tryptophan, pheny.'.alanine, etc.

(ii ) Non-essential synthesised in the body and do not need to be taken f:om outside, e.g. alanine, arginine,
aspartic acid, glutamin, cysteine, proline, serine, hystidine, tyrosine.

• In stomach proteins ;1re first broken down in amino acids then are digested. Hence, amino acids are the
substances, which are never excreted out through urine under normal circumstances in any healthy individual.

• 10 g of protein may yield 5.65 kcal energy.

• Daily requirement of protein is 70-100 g.

• Excessive thinning of hair in man is due to low protein content.

• They build up various protoplasmic structures including cell membrane.

• Main sources of protein are groundnuts, soybean, meat,pulses, fish, egg, milk, etc.

Functions of Proteins

• Essential for growth and repair of body.

•Act as enzymes or biological catalyst in metabolic reactions.

• Antibodies are proteins, which work for the defence of body.

• Collagen protein is present in bone, tendons, cartilage and transports fatty acids and lipids in blood.

• Insulin protein helps to regulate glucose metabolism.

• Keratin is present in skin, nails, hairs, horns, etc.

• Haemoglobin, visual pigments, cytochromes are proteins.

5. Minerals

• Metals, non-metals and their salts arc called minerals.

• These arc essential parts of enzyme (known as cofactors and prosthetic group) and vitamins.

Sodium (Na) and Potassium (K)

• These are main cations of extracellular and intracellular fluids.

• Sodium helps in absorption of glucose and electrochemical impulse conduction in nerves and

• Potassium takes part in muscles and nerves activity, glycogen and protein synthesis.

• Deficiency of sodium and potassium causes cramps and convulsions, respectively.

• Its sources are salt, milk, vegetables, etc.

Chlorine (CI)

• It is the main anion of extracellular fluid.

•It helps in synthesis of HCl in alimentary canal for food
digestion and acid-base balance.

• Deficiency of chlorine causes loss of appetite and muscle cramps.

• Its sources are salted food and sea food.

Magnesium (Mg)

• It is enzyme activator.

• It is a component of bones and teeth.

• Its deficiency produces convulsion and irregularity of

• Its sources are meat and green vegetables. Sulphur (S)

• It is the main constituent of many proteins, enzymes anc: coenzymes.

• Its deficiency disturbs protein metabolism.

• Its sources are dairy products, meat, eggs and broccoli. Cobalt (Co)

• It is a component of vitamin-B12 .

• Its deficiency causes pernicious anaemia.

• Its sources are meat, yeast and milk.

Fluorine (F)

• It maintains enamel and checks dental decay or caries.
• In excess, harmful to teeth and hnnes, i.e. caused fluorosis.

• It is prescllt in miilk and drinking water.

• Its sources are water supplies, tea, seafood, meat, liver
and beans.

Calcium (Ca)

• ft is a major component of bones and teeth. It is required for blood clotting and muscles contraction
and heart functioning.

• It is required more in children and pregnant ladies.

• It is present in milk, green vegetables, gram, fish, etc.

• Its dcficien.:y causes rickets, muscles spasms and tetany.
Iodine (I)

• It is essential for production of thyroxine hormone from thyroid gland.

Its deficiency causes goitre.

• Its sources .ue iodised salt, fish and seafood.

Phosphorus (P)

• Along with calcium, it occurs in bones and teeth.

• It is a component of nucleic acids, phospholipids and ATP.

• Its deficiency reduces growth, metabolism and causes rickets in children.

• Its sources are milk, cheese, eggs, peanuts and most foods.

Iron (Fe)

• It is an important component of haemoglobin.

• These arc required more in girls (35 mg) as compare to boys (25 mg). Because blood is loss in menstrual cyele
in girls.

• Its deficiency may leads to anaemia.

• Its sources are green leafy vegetables like spinach,
Chenopodium, methi, etc.

6. Vitamins

• These are accessory food factors, required in small quantity for controlling metabolism and body
functioning. They do not provide energy.

• Vitamins were discovered by Funk in 1912.

• These are of two types; fat soluble (A, D, E and K)
and water soluble (B-complex and C).

• Fat soublc vitamins are stored in liver.

• Eating of raw fish can cause the deficiency of vitamin-B

•Milk is a pool' source of vitamin-C.


lndigestable fibrous material present in the food is called roughage. It provides bulk to the diet for satisfying appetite.
Bulk amount of roughage helps in expanding gut and also stimulates peristalsis to eliminate the faecal mater.
Thus, food rich in roughage may help to prevent constipation, e.g. cellulose present in the cell walls of plant material such
as vegetables, fruits and bran all contain roughage.

Nutritional Deficiencies and Imbalances

• Protein Energy Malnutrition (PEM) It causes two types of diseases-kwashiorkor and marasmus.

(i) Kwashiorkor commonly affects children. Its symptoms are retarded growth, oedema, slender legs and bulging eyes.

(ii) Marasmus commonly affects infants under one year of age. Its symptoms are mental retardation and weak body,

wrinkled skin, thin limbs, loss of weight.

• Obesity causes by excess of food fat.

• Excess of vitamin-A, D and K causes hypervitaminosis.

• Excess of saturated lipids causes hypercholesterolemia.