NUTRITION
The Importance Of Various Dietary Components
 Dietary components called, nutrients are the
necessary constituents of food required by
organisms for growth and the maintenance of
life.
 There are five classes of nutrients that
contribute to an adequate diet.
 These may be divided into: Macronutrients and
micronutrients.
Macronutrients
These are proteins, fats and carbohydrates. They form the
main bulk of food. In the Indian dietary pattern, they
contribute to the total energy intake in the following
proportions:
Proteins
7 to 15%
Fats
35 to 45%
Carbohydrates
50 to 70%
 Protein, fat and carbohydrate are sometimes referred
to as proximate principle. They are oxidized in the
body to yield energy, which the body needs.
 Primary function of protein is to provide essential and
Non-essential amino acids for building of body
proteins.
 Fats are concentrated source of energy, provide
essential fatty acids which have a vitamin like
function in the body.
 Water is the solvent of the body and
transport vehicle for distributing nutrients to
the tissues. Water, although not a nutrient by
definition, is of course required to replace
the water lost in the urine, breath and sweat.
 Fiber also is not a nutrient but is being
considered as a necessary food component.
Micronutrients
These are vitamins and minerals
They are required in small amounts which may
vary from a microgram to several grams.
Vitamins and minerals play an important role in
the regulation of the metabolic activity in the
body and help in the utilization of proteins, fats
and carbohydrates.
Minerals are also used for the formation of body
structure and skeleton.
Role of
Macronutrients
Carbohydrate
1. Available or digestible carbohydrate
2. Unavailable or undigestible carbohydrate.
 The digestible carbohydrates are a major source
of food energy, yielding 4 kcal/gm and provides
about 50 to 70% of the energy requirement. In
addition, these carbohydrates have protein
sparing effect.
 Unavailable or undigestible carbohydrates
provide dietary fiber.
Carbohydrate requirement
 The recommended intake of carbohydrate in
balanced diet is placed so as to contribute
between 50 to 70% of total energy intake.
 Most Indian diets contain amounts more than
this, providing as much as 90% of total energy
intake in some cases, which make the diet
imbalanced.
Dietary fiber
Dietary fiber is the name given collectively to indigestible
carbohydrates present in foods. These carbohydrates
consist of:
–
Cellulose
–
Pectin
–
Gums
–
Mucilages.
 The dietary fiber is not digested by the enzyme of the
human gastrointestinal tract, where most of the other
carbohydrates like starch, sugars are digested and
absorbed.
 Plant foods are the only sources of dietary fiber. It is
found in vegetables, fruits, and grains.
Importance of fiber
 Water holding capacity: The dietary fibers have a
property of holding water and swell like sponge with a
concomitant increase in viscosity. Thus, fiber adds bulk
to the diet and increases transit time in the gut (gastric
emptying time) due to high viscosity.
 Adsorption of organic molecules: The organic molecules
like bile acids, neutral sterols, carcinogens, and toxic
compounds
can be adsorbed on dietary fiber and
facilitates its excretion.
 It increases stool bulk: The fiber absorbs water
and increases the bulk of the stool and prevents
constipation by increasing bowel movements.
 Hypoglycemic effect of fiber: Recent studies have
shown that gum present in fenugreek seeds (it
contains 40% gum) is most effective in reducing
blood sugar and cholesterol levels.
 Hypocholesterolemic effects of fiber: Fiber has
cholesterol lowering effect. Fiber binds bile acids
and cholesterol, increasing their fecal exertion and
thus decreasing plasma and tissue cholesterol
level.
Significance of dietary fiber in medicine
High fiber diet reduces the risk of:
 Coronary heart disease (CHD)
 Colon cancer
 Diabetes
 Diverticulosis
 Haemorrhoids (piles).
Adverse effect of dietary fiber
Dietary fiber binds some mineral elements and prevents
their absorption. Thus, high dietary fiber intake may lead
to deficiency of mineral elements.
Fats
 Dietary fats are high energy yielding nutrients that
provide 35 to 45% of the caloric intake. Fat yields 9
kcal/gm.
 Besides satisfying metabolic energy needs, there are two
essential functions of dietary fat.
1. A vehicle for the absorption of the fat soluble vitamins
2.
To supply essential fatty acids, linoleic acid and linolenic
acid to the body.
 Dietary lipid also increases the palatability of
food and produces a feeling of satiety.
Fat requirement
 The daily requirement of fat is not known with certainty.
 During infancy, fats contribute to a little over 50% of the
total energy intake.
 This scales down to about 20% in adulthood.
 The ICMR Expert Group has recommended an intake of
20% of the total energy intake as fat of which at least
50% of fat intake should consist of vegetable oils rich in
essential fatty acids.
Protein And Amino Acids
 Proteins are important constituent of tissues and cells of
the body. They form the important component of muscle
and other tissues and vital body fluids like blood.
 The proteins in the form of enzymes and hormones are
concerned with wide range of vital metabolic processes in
the body.
 Protein as antibodies helps the body to defend against
infections.
 Proteins supply essential and nonessential amino acids for
the synthesis of protein and nitrogen for the synthesis of
several key compounds such as neurotransmitter and
heme.
 The amino acids, which are not used for protein
synthesis, are broken down to provide energy, which is a
wasteful way of using proteins (this is not their primary
function).
Diet should contain adequate carbohydrate and fat to
provide energy so that the proteins in the diet are most
economically used for the formation of body proteins to
fulfil other functions essential to life.
Essential amino acids
 Any amino acid that humans either cannot synthesize or
are unable to synthesize in adequate quantity is termed
“essential” and rest of the amino acids are called
“nonessential” as they can be formed in the body.
 An essential amino acid must be provided in the diet.
Deficiency of an essential amino acid impairs protein
synthesis and generally causes negative nitrogen balance,
 Ten of the twenty amino acids found in proteins are
essential for humans
 Of the 10 essential amino acids, 8 are essential at all
times during life. The other two namely histidine and
arginine are required in the diet during periods of
rapid growth as in childhood and pregnancy and
called semi essential.
NITROGEN BALANCE
 Catabolism of amino acids leads to a net loss of nitrogen
from the body. This loss must be compensated by the
diet in order to maintain a constant amount of body
protein.
 Nitrogen balance studies evaluate the relationship
between the nitrogen intake (in the form of protein) and
nitrogen excretion.
.
 Three situations of nitrogen balance are possible:
.
1.
Nitrogen equilibrium
2.
Positive nitrogen balance
3.
Negative nitrogen balance.
Nitrogen equilibrium
In normal adults, nitrogen intake = nitrogen excretion. The
subject is said to be in nitrogen equilibrium or balance.
Positive nitrogen balance
In this, nitrogen intake > nitrogen excretion, i.e. intake of
nitrogen is more than excretion.
This occurs in growing infants and pregnant women.
Negative nitrogen balance
In this, nitrogen intake < nitrogen excretion, i.e. nitrogen
output exceeds input, this occurs during serious illness and
major injury and trauma, in advanced cancer and
following failure to ingest adequate or sufficient high
quality protein, e.g. in kwashiorkor and marasmus.
If the situation is prolonged, it will ultimately lead to death
NUTRITIONAL
QUALITY OF PROTEINS
 Proteins present in different foods vary in their
nutritional quality because of the differences in their
amino acid composition. The quality of protein depends
on the pattern of essential amino acids it supplies.
 The best quality protein is the one which provides
essential amino acid pattern very close to the pattern of
the tissue proteins.
 Egg proteins, human milk protein, satisfy these criteria
and are classified as high quality proteins and serve as
reference protein for defining the quality of other
proteins.
Assessment of Protein Quality
The quality of a protein is assessed by comparison to the
“reference protein”, which is usually egg protein. Four
methods of assessment of protein quality are:
1.
Chemical score or amino acid
2.
Net protein utilization (NPU)
3.
Protein efficiency ratio (PER)
4.
Biological value (BV).
Protein requirement
 The requirement is dependent on the quality of dietary
protein.
 The ICMR Expert Group, suggested an intake of one
gram of protein per kg of body weight for adult males
and females
 The requirement should be nearly double for growing
children, pregnant and lactating women.
Normal Dietary Requirements
 The term ‘recommended dietary allowance (RDA)’
is defined as the amount of nutrient sufficient for the
maintenance of health in nearly all individuals.
 Estimates of allowances are based on the defined
minimum requirement plus a safety margin for most
individuals.
 Several terms have been used to define the amount of
nutrients needed by the body, such as:
−Optimum requirements.
−Minimum requirements.
−Recommended dietary allowances or intake, and
−Safe level of intake.
 Recommended dietary intake or allowance (RDA) has
been widely accepted.
Energy requirements

The energy requirement of an individual is defined as
the energy intake which will balance energy expenditure
in an individual, whose body size and composition and
level of physical activity are consistent with long-term
good health.
 For children and for pregnant and lactating women,
allowances are additionally made for growth of tissue and
production of milk.
 Energy intake has to be adequate to meet energy expenditure,
otherwise the body’s reserves will be utilized without being
properly replenished, resulting in loss of body weight,
impairment of various body functions and finally death.
 If, on the other hand, the energy intake is excessive, compared
to the energy expenditure, the body’s fuel reserves will
increase, resulting in obesity which is also a health risk.
 The energy value of food has long been expressed in
terms of the kilo-calorie (kcal), or abbreviated “Cal”
with capital “C”.
 This has been replaced by “joule” expressed as J, which
has been accepted internationally, however, the use of
kilocalorie for measuring energy still continues.
1 kcal
=
4184 J
1 kcal
=
4.184 kJ
1000 kcal =
4.184 MJ.
All energy in the diet is provided by three nutrients:
 Carbohydrate
 Fat
 Proteins
 Ethanol if it is consumed.
They supply energy at the following rates:
Protein:
4 kcal/g or 17 kJ
Fat:
9 kcal/g or 38 kJ
Carbohydrate:
4 kcal/g or 17 kJ
Ethanol:
7 kcal/g or 29 kJ
The energy content of fat is more than twice that of
carbohydrate or protein. If an adequate energy supply is not
provided, some protein will be burnt to provide energy.
Factors Affecting Energy Expenditure
The energy expended by an individual depends on four main
factors:
1. The basal metabolic rate (BMR).
2.The thermogenic effect (specific dynamic actions,
SDA) of food.
3.Physical activity, and
4.Environmental temperature.
Besides the above four factors extra provision of energy has to
be made for growth, pregnancy and lactation.
Basal Metabolic Rate (BMR)
The BMR is the energy expenditure necessary to maintain
basic physiologic functions:

The activity of the heart

Respiration

Conduction of nerve impulses

Ion transport across membranes

Reabsorption in the kidney
Definition of BMR
It is defined as the energy expenditure at rest, awake (but
not during sleep), in a thermo neutral (warm) environment
8 to 12 hours after the last meal and 8 to 12 hours after any
significant physical activity.
Factors affecting BMR
Gender or sex: The BMR of the males is slightly higher than
that of females.
Age: Decline in BMR with increasing age is probably
related to loss of muscle mass (lean body mass) and
replacement of muscle with adipose tissue that has lower
rate of metabolism.
Nutritional state: BMR is low in starvation and
undernouri• shment as compared to well fed state.
Body size or surface area: The BMR is directly
propor• tional to the surface area of the subject.
Body composition: The BMR is proportionate to lean body
mass, (LBM).
Endocrinological or hormonal state: In hyperthyroi• dism,
the BMR is increased and in hypothyroidism it may be
decreased by up to 40%, leading to weight gain.
Environmental temperature or climate: In colder climate,
the BMR is higher and in tropical climates the BMR is
proportionally low. Stress, anxiety and disease states,,
fever, burns and cancer also increase the BMR.
Drugs: Smoking (nicotine), coffee (caffeine) and tea
(theophylline) increase the BMR
Normal values of BMR
 BMR values are expressed as kcal per square meter of
body surface per hour. In adults, BMR for:
–
Healthy males is 40 kcal/sqm/hour
–
Healthy females, it is 37 kcal/sqm/hour.
 This means that the total caloric expenditure in 24 hours
to complete basal state is 1800 kcal for adult males and
1400 kcal for adult females, assuming that the total body
surface areas are 1.8 sqm and 1.6 sqm respectively.
Clinical application of BMR
 Determination of BMR is useful for the diagnosis of
disorders of thyroid.
 In hypothyroidism, BMR is low while in hyperthyroidism
it is elevated.
 BMR is used in calculating caloric requirements of an
individual and planning of diets.
The Thermogenic Effect (Specific Dynamic Action,
SDA) of Food
 This is the energy expended in the digestion,
absorption, storage and subsequent processing of food.
 This is called thermogenic effect of food because these
energy requiring processes generate heat.
 The thermogenic effect of food is equivalent to about 5
to 10% of total energy expenditure.
 This effect was originally attributed solely to the
metabolic processing of protein and was termed
‘specific dynamic action’(SDA), but it is now
recognized as an effect produced by the consumption of
all dietary fuels.
 The consumption of protein produces the greatest
energy loss compared to fat or carbohydrate.
 The thermogenic effect of food is :
–
Protein 20 to 30% of intake
–
Fat 2.5 to 4% of intake
–
Carbohydrate 5 to 6% of intake.
 It varies considerably from individual to individual.
.
BALANCED DIET
Definition of balanced diet
A balanced diet is defined as one which contains a variety of foods
in such quantities and proportions that the need for energy, amino
acids, vitamins, minerals, fats, carbohydrate and other nutrients is
adequately met for maintaining health, vitality and general wellbeing and also makes a small provision for extra nutrients to
withstand short duration of illness.
Balanced diet suggested by ICMR
 The dietary pattern varies widely in different parts of the world. It is
generally developed according to the:
 Kinds of food produced (which depends upon the climatic
conditions of the region)
 Economic capacity
 Religion
 Customs
 Tastes and habits of the people.
During pregnancy and lactation, additional
food is required.
For nonvegetarians, ICMR has recommended
substitution of a part of pulses by animal food
NUTRITIONAL DISORDERS
 When balanced diet is not consumed by a person for a
sufficient length of time, it leads to nutritional
deficiencies or disorders. This nutritional status is called
malnutrition.
 The most common nutritional disorders are :
Protein Energy Malnutrition (PEM) also
called Protein Caloric Malnutrition
(PCM)
Classification of PEM
Marasmus
Kwashiorkor
Marasmus or non edematous PEM
 Marasmus is a chronic condition resulting from a deficiency of both
protein and energy.
 Marasmus occurs in famine (extreme scarcity of food) areas when infants
are weaned from breast milk and given inadequate bottle feedings of
thin watery gruels (liquid food) of native cereals or other plant foods.
 These watery gruels are usually deficient in both calories and proteins.
 Marasmus is characterized by:
–
Growth retardation
–
Anemia
–
Fat and muscle wasting.
 Severe loss of body fat and muscle results in an emaciated
appearance.
 Starvation adaptations cause serum protein and electrolyte
concentrations to remain within their normal range and do
not show edema.
Kwashiorkor or edematous PEM
Kwashiorkor refers to conditions caused by severe
protein deficiency in individuals with an adequate
energy intake.
Kwashiorkor is an African word that means
“weaning disease”.
When children are weaned from protein rich breast
milk, they receive insufficient protein.
 The clinical symptoms of kwashiorkor include:
–
Anorexia
–
Severe edema associated with hypoalbuminemia
–
Moon face
–
Depigmented hair and skin
–
Fatty liver
–
Distended abdomen (due to enlarged liver).
Obesity
 This is the pathological state resulting from the consumption
of excessive quantity of food over an extended period of time.
 Obesity is defined as an accumulation of excess fat in the
body.
 The problem of obesity arises due to an imbalance of energy
intake in relation to energy expenditure.
The degree of obesity is assessed by means of the
body mass
index (BMI)
Body weight (kg)
BMI = —————————
Height (m2)
The causes of obesity
 Metabolic
 Hormonal
 Genetic.
Metabolic:
 Due to accumulation of triacylglycerol. Caloric intake exceeds
the amount needed for body function and the amount of work
being done.
 Deficiency of the enzyme ATPase which impairs normal
energy metabolism and gain more weight.
Hormonal:
 Due to endocrine disorders like:

Hypothyroidism

Hypogonadism

Hypopituitarism

Cushing’s syndrome.
Genetic:
 Several genes have the potential to cause obesity in humans, e.g. mutation in
leptin gene (ob gene) results in obesity.
 Leptin leads to supression of food intake. Grossly obese humans have a failure in
production of leptin.
Obesity as a health risk
An obese person has the risk of:
 Hypertension
 Coronary heart disease and stroke
 Insulin resistant diabetes mellitus
 Atherosclerosis
 Cancer