• Nutrition is the science of food and its relationship to health –
how the human body uses food and processes the nutrients it
contains to enable the body to perform functions (i.e. the heart
to beat, the lungs to breathe, the kidneys to filter blood, the
brain to think etc.).
• Energy is the capacity to do work. Through the process of
digestion, we convert the food we eat to energy.
• Our bodies need energy to grow and repair themselves, keep
warm and do physical activity. Energy comes from food and
drink, in particular from carbohydrates, protein, fat and alchol.
• Energy is defined as the capacity to do work.
• Energy is the strength and vitality required for sustained
physical or mental activity.
• Energy requirement is the amount of food energy
needed to balance energy expenditure in order to
maintain body size, body composition and a level of
necessary and desirable physical activity consistent with
long-term good health.
• This includes the energy needed for the optimal growth
and development of children, for the deposition of tissues
during pregnancy, and for the secretion of milk during
lactation consistent with the good health of mother and
4. Unit of energy
• The food energy is calculated as Calories (C) or
kilocalories (kcal) or Joules (J).
• Calorie; The qualitative food requirements are estimated in
terms of energy in Calorie.
• One kilocalorie is equal to 1000 calories.
• One Kcal is equal to 4.186 Joules
• One gram of protein or carbohydrate provides 4 kcal
whereas one gram of fat provides 9 kcal.
• In nutrition calorie and kilocalorie are sometimes used to
mean the same thing.
5. Energy requirement of different categories
• The recommended level of dietary energy intake for a
population group is the mean energy requirement of the
healthy, well-nourished individuals who constitute that
9. COMPONENTS OF ENERGY REQUIREMENTS
Human beings need energy for the following:
• Basal metabolism. This comprises a series of functions that are
essential for life, such as cell function; the synthesis, secretion and
metabolism of enzymes and hormones to transport proteins and
other substances; the maintenance of body temperature;
uninterrupted work of cardiac and respiratory muscles; and brain
• Basal metabolic rate (BMR): The minimal rate of energy
expenditure compatible with life. It is measured in the supine
position under standard conditions of rest, fasting, immobility,
thermoneutrality and mental relaxation. Depending on its use, the
rate is usually expressed per minute, per hour or per 24 hours.
• Depending on age and lifestyle, BMR represents 45 to 70 percent
of daily total energy expenditure, and it is determined mainly by
the individual’s age, gender, body size and body composition.
10. • Metabolic response to food. Eating requires energy for
the ingestion and digestion of food, and for the absorption,
transport, inter conversion, oxidation and deposition of
• These metabolic processes increase heat production and
oxygen consumption, and are known by terms such
as dietary-induced thermogenesis, specific dynamic
action of food and thermic effect of feeding.
• The metabolic response to food increases total energy
expenditure by about 10 percent of the BMR over a 24-
hour period in individuals eating a mixed diet.
• Physical activity. This is the most variable and, after
BMR, the second largest component of daily energy
expenditure. Humans perform physical activities.
11. • Discretionary activities, include the regular practice of
physical activity for fitness and health; the performance of
optional household tasks that may contribute to family
comfort and well-being; and the engagement in individually
and socially desirable activities for personal enjoyment, social
interaction and community development.
• Growth. The energy cost of growth has two components: 1)
the energy needed to synthesize growing tissues; and 2) the
energy deposited in those tissues. The energy cost of growth
is about 35 percent of total energy requirement during the
first three months of age, falls rapidly to about 5 percent at 12
months and about 3 percent in the second year, remains at 1
to 2 percent until mid-adolescence, and is negligible in the
12. • Pregnancy. During pregnancy, extra energy is needed for
the growth of the foetus, placenta and various maternal
tissues, such as in the uterus, breasts and fat stores, as
well as for changes in maternal metabolism and the
increase in maternal effort at rest and during physical
• Lactation. The energy cost of lactation has two
components: 1) the energy content of the milk secreted;
and 2) the energy required to produce that milk. Well-
nourished lactating women can derive part of this
additional requirement from body fat stores accumulated
13. BMI ( Body Mass Index)
• Body mass index (BMI) is an estimate of body fat based on height and
weight. It doesn’t measure body fat directly, but instead uses an
equation to make an approximation. BMI can help determine whether a
person is at an unhealthy or healthy weight.
• Body Mass Index Formula
BMI is calculated by dividing a person’s weight by the square of their
BMI Weight Status
Below 18.5 Underweight
18.5 – 24.9 Normal
25.0 – 29.9 Overweight
30.0 and above Obese
Adults age 20 and older can interpret their BMI based on the following
standard weight status categories. These are the same for men and women
of all ages and body types:
15. • Body Mass Index for Children;
BMI is interpreted differently for people under age 20.The
implications for children and adolescents can vary depending on
age and gender. The amount of body fat changes with age. It’s
also different in young boys and girls. Girls usually acquire a
higher amount of body fat and develop it earlier than boys.
For children and teens, the CDC uses age growth chartsTrusted
Source to show BMI as a percentile ranking. Each percentile
expresses a child’s BMI relative to other children of the same
age and gender. For example, a child would be considered
obese if they had a BMI that landed at or above the 95th
percentile. This means that they have more body fat than 95
percent of children in the same age and gender category.
16. Percentile Weight Status
Below 5th Underweight
5th to 85th Normal or healthy weight
85th to 95th Overweight
95th and above Obese
The following table shows the percentile range for each weight status:
17. • For children and teens, BMI is age- and sex-specific and
is often referred to as BMI-for-age. In children, a high
amount of body fat can lead to weight-related diseases
and other health issues. Being underweight can also put
one at risk for health issues.
• A high BMI can indicate high body fatness. BMI does not
measure body fat directly, but BMI is correlated with more
direct measures of body fa
18. Determinants and factors affecting basal
metabolic rate/ Energy Expenditure
1. Muscle mass. The amount of muscle tissue on the body.
Muscle requires more energy to function than fat. So the more
muscle tissue the body carry, the more energy body needs just
to exist. (Resistance or strength training is most effective for
building and maintaining mass.)
2. Age. As we get older, metabolic rate generally slows. This is
because of a loss of muscle tissue and changes to hormonal and
neurological processes. During development children go through
periods of growth with extreme rates of metabolism.
3. Body size. Those with bigger bodies have a larger BMR
because they have larger organs and fluid volume to maintain.
4. Gender. Men generally have faster metabolisms than women.
5. Genetics. Some families have faster BMR than others with
some genetic disorders also affecting metabolism.
19. 6. Physical activity. Exercise increases muscle mass and
powers up metabolic engines burning kilojoules at a faster
rate, even when at rest.
7. Hormonal factors. Hormonal imbalances such as hypo
& hyperthyroidism can affect metabolism.
8. Environmental factors. Environmental changes such
as increased heat or cold forces the body to work harder to
maintain its normal temperature and increases BMR.
9. Drugs. Caffeine and nicotine can increase BMR while
medications such as antidepressants and steroids increase
weight gain regardless of what we eat.
10. Diet. Food changes the body’s metabolism. What and
how we eat has a big influence on BMR.
20. Normal BMR value
• An average man has a BMR of around 7,100 kJ per day,
while an average woman has a BMR of around 5,900 kJ
per day. Energy expenditure is continuous, but the rate
varies throughout the day. The rate of energy expenditure
is usually lowest in the early morning.