INTRODUCTION
What is “Food” and what is “Nutrition”?
Food is any edible material that supports growth,
repair and maintenance of the body. Food also
protects the body from infections and diseases.
Nutrition is the process by which body utilizes food
for growth and maintenance and healthy living.
Food functions in the body through the nutrients
it contains
What are nutrients?
Nutrients are substances found in food. These are:
•Carbohydrate
•Fat/Oil
•Protein
•Vitamins
•Minerals
 Since Water is indispensable for life, it is considered
both as a food and as a nutrient.
 Dietary Fibre and some Phytochemicals of plant foods,
although not nutrients as such, are needed for good
health.
•
What food does in the body does through the
nutrients it contains. The body utilizes these
nutrients to grow and keep healthy and strong. All
nutrients needed by the body are available
through food.
•
No food by itself (except for breastmilk which is
adequate for babies up to six months of age) has
all the nutrients needed for full growth and health.
Food therefore must be balanced.
•
We therefore need a variety of foods to get all the
nutrients the body needs.
Each nutrient has its own function in the body.
Specific nutrients do their best work in the body
when present with other nutrients.
Nutrients are therefore mutually supportive.
What are Macronutrients and Micronutrients?
The nutrients can be divided into two major groups –
“Macronutrients” and “Micronutrients”.
Macronutrients are those that are needed in large
quantities (tens or hundreds of grams) every day.
These are: Carbohydrates, protein and fats/oils.
Micronutrients are those that are needed in minute
quantities (micrograms or at best milligrams). These
are vitamins, minerals and trace elements.
Carbohydrates
Main function is energy production in the body.
Largest source of energy: 40 - 80 percent of the total
energy intake in different countries. Neither extreme
is good. The ideal contribution is 60 percent.
One gram of carbohydrate provides 4 Kcal.
Grains (rice, wheat, maize), roots and tubers (potato,
sweet potato, guam, banana) and legumes (pulses,
nuts) are rich sources of carbohydrates.
Sweet fruits and some vegetables also provide
carbohydrate in the form of sugar.
Milk sugar is lactose.
Honey has high content of fructose, the sweetest of all
sugars.
Soft drinks contain sugar but almost no other
nutrients.
Carbohydrates are present in two forms:
Simple carbohydrates: glucose, fructose, sugar
Compound carbohydrates: starch in plants
and glycogen in animals (liver and muscles)
Compound carbohydrates are polymers of
glucose.
Carbohydrates and sugars
Digestion in the intestine
Glucose (plus other monosaccharides)
Absorbed into blood
In presence of insulin
Taken up by cells
In presence of O2
Metabolized to CO2 + H2O + Energy
(no side effects in glucose use in the body)
During well-fed conditions, body glucose is stored in
liver and muscles as glycogen, a compound
carbohydrate. Glycogen is therefore the animal
counterpart of plant starch.
During starvation, glycogen of liver and muscle is
broken into glucose to provide energy.
Glucose is the only metabolic fuel for the brain under
normal conditions.
Carbohydrates taken in excess of energy requirements
are directly converted into fat and deposited in the
body.
Protein
Protein is the building material for all body parts, such as
muscle, brain, blood, skin, hair, nails, bones and body
fluids.
It is essential for growth, repair of worn-out tissues,
replacement of used-up blood and resistance against
infections.
Protein comes from both animal and plant foods.
Meat, fish, egg, and milk and milk products are rich
sources of animal protein.
Pulses, nuts and beans are rich sources of plant protein.
Cereals are low in protein (e.g. rice: 6 – 8%, wheat: 12 –
14%), but because of their large quantities in the diet, they
meet a major portion of total dietary protein requirement.
Animal proteins are of high quality (“first-class”
proteins) because of their more complete and balanced
composition of amino acids.
Plant proteins are of lower quality (“second-class”
proteins) because they are incomplete in one or more of
the essential amino acids.
Combination of two or more plant foods can mutually
supplement each other’s deficiency and therefore give
rise to high quality protein. For example, khichuri, which
is a mixture of rice and dal (pulse), is a good quality diet.
The protein from beans and legumes are of better
quality than the protein from rice and wheat
products. These foods are considered less expensive
meat substitutes and are often called the ‘poor man’s
meat’.
Potato is poor in protein (<3%), but this protein is of
high quality.
Proteins are polymers of smaller units called
amino acids, some of which can be manufactured
in the body (so-called “non-essential”), and others
must be provided pre-formed by food (the
essential amino acids).
Protein
Digestion in the
gastro-intestinal tract
Amino acids
Absorbed into blood
Taken up by the cells
Synthesize body proteins
Although the main function of protein is to
build and maintain the body, it also gives
energy.
One gram of protein gives 4 Kcal.
Fats/Oils
Fats/oils are concentrated sources of energy needed
by the body.
The term “fat” is commonly used to refer to a family
of compounds called “lipids” which are waterinsoluble.
They include triglycerides, phospholipids and sterols
such as cholesterol. Triglycerides predominate both in
the food and in the body.
1 gm of fat provides 9 kcal, i.e. more than double the
energy given by carbohydrate or protein per unit
weight.
Chemically, triglycerides are fatty acid tri-esters of
glycerol:
H2C – O – CO – fatty acid
HC – O – CO – fatty acid
H2C – O – CO – fatty acid
Fats
A triglyceride may be a FAT or OIL, depending on
the predominant type of fatty acids it contains:
saturated, monounsaturated and polyunsaturated.
When predominant fatty acids are saturated and
monounsaturated, then it is solid at room
temperature and is termed as FAT.
Usually, triglycerides of land animal sources are FATs.
Examples are fats of beef, mutton, goat and chicken skin.
Saturated fatty acids are cholesterologenic, i.e. they
increase blood cholesterol level.
Aquatic animals like the fish, especially the marine fish,
have good preponderance of polyunsaturated fatty acids
and their fat is actually OIL.
Oils
When polyunsaturated fatty acids predominate, then
it is liquid at room temperature and is termed as OIL.
Usually, triglycerides of plant sources are OILs.
Examples are vegetable oils - mustard oil, soybean
oil, sunflower oil, corn oil and other cooking oils.
However, coconut and palm oil contain large
proportions of saturated and monounsaturated fatty
acids.
Cholesterol
Some food items are rich in preformed
cholesterol. Examples: egg yolk, liver, brain,
chicken skin.
Forms of blood cholesterol
HDL
=
Good cholesterol
LDL
=
Bad cholesterol
Fat provides the building materials for some body
parts, such as brain, nerves and hormones.
It also facilitates absorption, transport and storage of
fat-soluble vitamins A, D, E and K.
Fat is therefore an essential nutrient. Like all other
nutrients, fat is beneficial if consumed in the right
amount and if it is the right type.
Since high blood cholesterol is a risk factor for
coronary heart disease, diet rich in preformed
cholesterol and saturated fat is to taken with caution
after a certain age. It is, however, not a problem for
infants and young growing children.
Vitamins
•
Vitamins are food constituents vital for life.
They cannot be synthesized in the body and
must therefore be taken with food. They are,
however, needed in minute amounts.
•
Vitamins help in the metabolism and utilization
of the carbohydrate, protein and fat in the cells.
They act as helpers (coenzymes) of enzymes
involved in these metabolisms.
•
Vitamins thus help regulate body functions and
maintain health. They also protect the body
against infections.
Vitamins are either water-soluble or fat-soluble.
•
Water-soluble vitamins
vitamins and vitamin C.
•
B-complex vitamins are vitamin B1, B2, B6, B12,
niacin, folic acid, biotin, pantothenic acid.
•
Fat soluble vitamins are vitamins A, D, E and K.
are
the
B-complex
•
Soluble vitamins, when taken in excess of body
needs, are excreted in urine.
•
On the other hand, fat-soluble vitamins,
when taken in excess, are stored in the body
(particularly liver) for use at times when the
intake of these vitamins is inadequate.
•
Most vitamins can be derived from liver,
fruits, vegetables, legumes and grains.
A few of the key roles and rich dietary sources of
some vitamins of public health importance are listed
in the table below.
Function
Rich sources
Helps release energy from
nutrients; supports normal
appetite and nerve function
Cereal grains, pulses, yeasts;
Helps release energy from
nutrients; supports skin health;
prevents deficiency manifested by
cracks and redness at corners of
mouth, inflammation of the tongue
and dermatitis
Helps release energy from
nutrients; supports skin, nervous
and digestive systems
Milk and its non-fat products;
Pyridoxine
(Vitamin B6)
Helps make red blood cells; helps
in amino acid and fatty acid
metabolism
Widely present in both plant and animal
foods
Folic acid
Helps in the formation of DNA and
new blood cells including red blood
cells; prevents anemia, some birth
defects, heart disease
Thiamin
(vitamin B1)
Riboflavin
(vitamin B2)
Niacin
Green vegetables, fish, meat, fruit, milk
Green vegetables, meat, fish, egg
Liver, ground nuts, cereal bran or germ
Dark-green leaves, liver, kidney
Vitamin C
Vitamin A
Vitamin D
Vitamin E
Helps in the formation of protein,
collagen, bone, teeth, cartilage,
skin and scar tissue; facilitates the
absorption of iron from the
gastrointestinal tract; involved in
amino acid metabolism; increases
resistance to infection
Fruits, vegetables and dark-green leaves
Maintains normal vision, skin
health, bone and tooth growth,
reproduction and immune
function, prevents xerophthalmia
Animal sources: Butter, eggs, milk,
liver;
Plant sources: Dark-green leafy
vegetables, mangoes, papaya, tomato
Helps in the mineralization of
bones by enhancing absorption of
calcium
Fish liver oils, eggs, cheese, milk and
butter; Sunlight induces synthesis of vit.
D in the body from skin cholesterol.
Strong antioxidant; helps prevent
atherosclerosis; protects
neuromuscular system; important
for normal immune function
Vegetable oils, germinated whole-grain
cereals
Minerals
Minerals are inorganic chemical elements present
throughout the body in varying amounts. Like the
vitamins, they cannot be synthesized in the body and
must be taken with food.
Minerals act as co-factors of enzymes for metabolism.
Minerals form part of the structure of body tissues,
such as bones, teeth and nails, blood, nerves and
muscles.
Minerals are vital to physical and mental
development. They also help protect the body
against infections.
Meat, fish, milk, cheese, green leafy vegetables and
legumes provide most of the minerals needed by
the body.
Some of the key roles of minerals are shown in the table below.
Mineral
Function
Calcium
Mineralization of bones and teeth; regulator of many of the
body’s biochemical processes; involved in blood clotting,
muscle contraction and relaxation, nerve function, blood
pressure and immune defenses
Phosphorous
Mineralization of bones and teeth; part of every cell; used in
energy transfer and maintenance of acid-base balance
Sodium
Maintains normal fluid and electrolyte balance, assists
nerve impulse initiation and muscle contraction
Chloride
Maintains normal fluid and electrolyte balance
Chromium
Works with insulin and is required for release of energy
from glucose
Copper
Necessary for absorption and use of iron in the formation of
hemoglobin
Fluoride
Involved in the formation of dental enamel and
prevents dental caries; involved in the formation of
teeth and skeleton and inhibits osteoporosis in old age
Iodine
As part of the two thyroid hormones, iodine regulates
growth, physical and mental development and
metabolic rate
Iron
Essential in the formation of blood; involved in the
transport and storage of oxygen in the blood and is a
cofactor bound to several non-heme enzymes required
for the proper functioning of cells
Sulfur
Integral part of vitamins, biotin and thiamin, as well as
the hormone insulin
Zinc
Essential for normal growth, development,
reproduction and immunity
Magnesium
Involved in bone formation and tissue energy
metabolism
Dietary Fibre
•
Dietary fibres are non-digestible, non-absorbable
components of food.
•
Fibres form the bulk of the stool and help in
clearing the bowel and in preventing constipation
and colon cancer.
•
Fibres inhibit absorption of glucose and cholesterol
from the GI tract, thus are helpful in diabetes and
heart disease.
•
Fruits, vegetables, pulses and whole cereals are
sources of dietary fibre.
•
Our daily diet should contain some fibre for good
health and well being.
Non-nutrient components of health significance
•
Some plant foods show additional health benefits
beyond basic nutrition. These foods are called
“Functional Foods”.
•
These ingredients protect our body from various
diseases like diabetes, hypertension, and some forms of
cancer.
•
Bright examples of functional foods are tomatoes,
mushroom, apple and guava, garlic, onion, ginger,
cloves and other spices, cabbage, cauliflower, broccoli,
blackberry, and tea.
•
The above functional foods should be a part of our daily
dietary.