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ENERGY
Energy is defined as the ability to do work. Energy exists in several forms.
The forms of energy important in nutrition are:
1. Chemical energy in food.
2. Light or solar energy for synthesis of vitamin D in the skin and for
photosynthesis is plants.
3. Mechanical energy for movement of muscles.
4. Electrical energy for functioning of the brain and verve cells.
5. Heat energy, generally produced when energy is converted from one form
to another. They energy from food is finally converted into heat energy.
UNITS OF MEASUREMENT
The energy present in food or the energy needed by the body is measured
in units called joules or calories. The calorie in nutrition is the large calorie or
kilocalorie. The kilocalorie is defined as the amount of heat required to raise
the temperature of 1 kg (1000g) of water by 1oC. This calorie is 1000 times
bigger than the calorie used in physics. The international unit for energy is the
joule (J) and it is the energy expended when 1 kilogram (kg) is moved 1 metre
(m) by a force of 1 newton (N).
Scientists and nutritionists are concerned with large amounts of energy,
so they use the units kilocalorie, kilojoules (kJ= 103J), or megajoule (MJ=106J)
to express energy.
1 kilocalorie = 4.184 kilojoules
1 megajoule = 239 kilocalories
ENERGY VALUE OF FOOD
The energy content of various foods can be measured in two ways: by
calorimetry or by proximate composition.
Calorimetry
The bomb calorimeter is based on the principle of calorimetry. It
measures the heat produced when the food sample is ignited by an electric
spark in the presence of oxygen and platinum which acts as a catalyst. The
bomb calorimeter is made of two main parts – an inner part in which a
measured quantity of food sample to be tested is placed and an outer portion
which contains a known volume of water. When the food sample is electrically
ignited, the surrounding water absorbs the heat produced. The energy value of
the food is calculated by measuring the rise in temperature of water, based on
the definition of the term calorie.
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Proximate Composition
This is a simpler and faster way of determining the calorie content of
food. The approximate carbohydrate, fat and protein content of a food given in
the food composition tables is multiplied by their fuel factor, i.e., calories
provided by 1 g of the nutrient and this total gives the energy value of the food.
• Carbohydrates – 4 kcal
• Proteins – 4 kcal
• Fats – 9 kcal
ENERGY NEEDS OF THE BODY
The energy requirement for an average healthy person is based on the
energy required to carry out basal processes as well as the energy cost of
activities one indulges in. The allowances are suggested for a reference man
weighing 60kg and a reference woman weighing 50 kg in the 20-39 year age
group.
Reference Man: The reference man is between 20-39 years of age and
weighs 60kg. He is in a state of good health, free from disease, and
physically fit for active work. He is moderately active and is employed
for 8 hours in moderate work. He spends 8 hours in bed, 4-6 hours
sitting or engaged in light work, and 2 hours in walking, active
recreation, or household chores. On an average his energy requirement is
2875 kcal.
Reference Woman: the reference woman is between 20-39 years of age
and weighs 50kg. She is moderately active and spends 8 hours in
routine household work. She spends 8 hours in bed, 4-6 hours sitting or
moving around and performing light activity, and 2 hours in walking,
active recreation, or household chores. On an average her energy
requirement is 2225 kcal.
BASAL METABOLIC RATE
The amount of energy required by the body for carrying out involuntary
work and maintaining the body temperature is known as the basal metabolic
rate (BMR). The involuntary work includes the functioning of various organs
and system which work continuously to keep the body processes going such as
the heart and blood circulation, the kidneys and excretion. Approximately one
third of this energy is needed for these processes while the remaining two
thirds is utilized for maintenance of muscle tone.
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Factors affecting the BMR
Many factors influence the BMR.
Body size: Heat is continuously lost through the skin. A tall well built person
has a greater skin surface area than shorter or smaller person and loses more
heat through the skin and hence has a higher BMR.
Body composition: The amount of muscle tissue and adipose or fatty tissue in
the body affects the BMR. An athlete with well built muscles and little body fat
has a higher BMR than a non athlete with more body fat of the same weight.
The metabolic activity in muscle tissue or lean tissue is much more as
compared to adipose or fatty tissue.
Age: During periods of rapid growth, the BMR increases by 15-20% because
the growth hormone stimulates cell metabolism and new cells are formed. It is
high during infancy, pre-school years, and puberty. During pregnancy and
location it rapidly increases once again. The BMR gradually decline with age at
the rate of 2% for each decade after the age of 21 years.
Sex: The BMR is 10% higher is male as compared to female. The difference in
BMR is attributed to a higher proportion of adipose tissue in females and
hormonal variations between the sexes.
Fever: Fever increases the BMR by 7% for each degree Fahrenheit rise in body
temperature. This is one of the reasons for loss of weight during fever.
State of health: The BMR is low during starvation and malnutrition because of
reduction in muscle tissue. In diseases and conditions where catabolic
processes are high such as cancers, tuberculosis, and burns, BMR is high.
Hormones: Disorders of the thyroid gland markedly influence the BMR.
Hyperthyroidism, a condition of excessive production of thyroid hormone
increases BMR, and hypothyroidism or decreased production of thyroid
hormone decreases BMR.
Climate: BMR rises when the climate is cold in order to maintain normal body
temperature. In very warm climates leading to profuse sweating, BMR may
increase by trying to reduce body temperature.
Psychological tension: Worry and anxiety increases BMR.
SPECIFIC DYNAMIC ACTION
Specific dynamic action (SDA) is a term used to describe the effect food
has in increasing the metabolic rate above the level found when fasting. Energy
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is needed to digest, absorb, and metabolize the food we eat. Food intake
stimulates the metabolism process leading to an increase in energy
expenditure. This is known as the thermogenic effect of food or the specific
dynamic effect. Proteins have maximum effects on SDA, increasing the BMR by
about 30% when eaten alone, while carbohydrates and fats show smaller
increases. When eaten together in a normal mixed diet, the increase is about 5-
10% of basal metabolism.
PHYSICAL ACTIVITY
Physical activity increases the energy requirement above the basal metabolism.
There is a wide variation in the energy required for physical activity among
individuals. Physical activity includes energy needed for work, recreation, and
mental activity, i.e., all voluntary activities. Some people use up more energy
for physical activity than for basal metabolism. On the basis of occupation,
activities are grouped under three heads.
• Sedentary work – teaching, office work, executive, housewife, tailoring.
• Moderate work – farming, industrial labour, driver, maidservant.
• Heavy work – stone cutter, miner, wood cutter.
ENERGY BALANCE
The human body is constantly using energy which needs to be replaced.
For this a constant supply of energy is required. Energy is used for basal
metabolism, specific dynamic action, and physical activity. The energy from the
food we eat, mainly carbohydrates and fats, is used to meet the energy
demands of the body. When food is not available during fasting or starvation,
the body draws upon its own stores to meet the energy needs of the body. The
body has three types of energy store.
Glycogen: The form is which carbohydrate is stored in the muscle and liver is
adequate to last for 12-48 hours. Approximately 300g glycogen is stored in the
muscle and 100g in the liver.
Muscle: Protein is stored in limited amounts in the muscle.
Adipose tissue: Fat is stored in the adipose tissue and the amount stored
varies vastly from one person to another.
A person in energy balance neither gains weight nor loses weight.
Excessive consumption of calories as compared to the output or activity leads
to a condition called over weight, which in severe cases is called obesity. A
deficient intake of carbohydrates and fats in the diet leads to underweight or
under nutrition. Both underweight and obesity are undesirable conditions
which need timely correction.
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Definition: Energy balance is a condition in which the energy provided by food
is nearly equal to the total energy expended by the body resulting in steady
body weight.
Energy balance: Energy output = Energy input
OVERWEIGHT
Overweight and obesity affect over 25% adults in developed countries and can
lead to serious health consequences if not treated early. When an individual’s
energy intake consistently exceeds energy expenditure, weight gain occurs
initially, leading to obesity. Since energy can neither be created nor destroyed
but can be changed from one form to another, the excess chemical energy from
food is converted into fat and stored as potential energy in the adipose tissues.
Overweight: A person whose body weight is 10% more than the prescribed
height for weight standards for his age and sex.
Obese: A person whose body weight is 20% or more than that of the prescribed
standards.
Grossly obese: A person who weighs 45kg or 100% more than accepted
standards.
Causes of obesity
• Family food habits – rich high calorie foods
• Ignorant of calorific value of food
• Skips breakfast, gobbles high calorie snacks
• Sedentary lifestyle
• Lower metabolism with increasing age but failure to reduce intake
• Emotional outlet- eats more to overcome worry, stress, etc.
• Attend many social events
• Distress eating ( to avoid wastage)
All obese people should lose one to two pounds per week. Physical
activity should be increased for faster weight loss and better muscle tone.
UNDERWEIGHT
Underweight is caused due to under nutrition which is the result of
ingesting insufficient quantity of food. An energy intake less than the need are
the most common cause. Other causes for underweight are poor assimilation of
food due to digestive disorders, faulty absorption, intestinal infections, poor
food habits, stress and tension, poverty and lack of nutrition knowledge.
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Under nutrition affects ones growth, health, behavior, and brain
structure and function. Such individuals should be prescribed a high calorie,
high protein, and moderate fat diet for gaining weight. An excess of 500
kcal/day will help in gaining 1 lb/week.
BODY MASS INDEX
The concept of ideal or desirable body weight has been changing from
time to time and ideal weight for different body frames was initially computed.
Today the weight of an individual is assessed on a more scientific basis known
as the body mass index (BMI).
Body mass index= weight in kilograms / (height in metres)2 = W/H2
On the basis of BMI, obesity is graded follows:
Obesity BMI
Grade 1 25-29
Grade 2 30-40
Grade 3 >40
DIETARY SOURCES
All foods provide energy. While selecting food one must consider the
other nutrients such as proteins, vitamins, minerals, and fibre present in the
food and make a wise choice.
The nutrients carbohydrates and fats are consumed mainly as a source
of energy. All refined carbohydrates i.e., sugars and starch and all foods rich in
fats are rich sources of energy.
The cereal group is another excellent source of energy and supplies the
highest percentage of calories.
Hollow calorie foods Nutrient dense foods
• Aerated soft drinks • Milk, cheese, yoghurt
• Synthetic syrups • Green leafy vegetables
• Candy and candy floss • Pulses, sprouts
• Chocolates • Soya beans, peanuts
• Iced cakes and fresh • Guava, amla
• Cream pastries • Liver, fish, meat
• Ice lolly • Eggs
• Puffy pastry • Flax seeds
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