1 The body has a constant need for energy to carry on the work of internal
organs and physical activity. It derives this energy from the burning or
combustion of food stuffs.
2 Energy is expended in —
a) maintaining body temperature at approximately 37o C;
b) promoting the action of vital organs such as the heart, lungs, liver and kidneys;
c) Performance of mechanical work.
Although the energy expenditure is highest at time of greatest activity, energy is also expended when the individual is sleeping.
3 The term which is used to describe the changes in the tissues by means of which the body derives energy from the food is “metabolism”. The energy expended in maintaining the body temperature and promoting the action of the vital progress when a person is awake, at complete rest, in a comfortable environment and in the pastaheorptive stage is called basal metabolism. It is the lowest expenditure of energy when a person is awake.
Measurement of energy
4 Food energy is measured by heat units, or calories. A calory is defined a the amount of heat required to raise temperature of one liter of water through one degree centigrade
Factors affecting energy requirement
5 There are other factors besides exercise which effect the energy requirement :-
a) Age : Relatively greater during the growing age.
b) Sex : Less for females
c) Size and body : A tall thin man has a greater need for energy
composition food than short fat man of the same weight.
d) Climate : Greater during cold climate.
e) Fever : Increases by 13 per cent for every degree centigrade
rise in temperature.
f) Sleep : Lowers metabolism
Specific dynamic action of foodstuffs
6 It is increase in the heat production over the basal level, when food is taken by an individual at rest. The increase varies with the type of food and is also called “calorigenic effect”.
7 The energy requirement for a man of average size are :-
a) Quiet, Indoor and sedentary life .. 2500—Calories
b) Light muscular work .. 2500—3000 Calories
c) Medium muscular work .. 3000—3500 Calories
d) Heavy muscular work .. 3500—Calories upward
Relative value and requirement of foodstuffs
8 Amount of heat given by three classes of food stuffs is as follows:
1 gm fact produces 9 Calories
1 gm protein (Produces ) When completely utilized
1 gm carbohydrate ( 4 Calories)
9 The following are required for a man of average size and weight :-
a) Proteins .. 10 to 15 percent of total
b) Carbohydrate .. 50-60 percent
c) Fat .. 25 to 35 percent