Energy requirements of human body

 Energy requirements of human body

The energy is quantitatively expressed as units of heat which in this case is the kilocalorie. It is the amount of heat required to raise the temperature of a litre of water by 1°C from 15°C to 16°C. However, recently we have the joule as the unit of energy and to convert 1 Kcal 4.19 K joules or 1 kilocalorie is equal to 4184 or 4188.5 or 4186.8 joules. Energy for physiological processes is provided by the combination of carbohydrates, fats and proteins. The daily energy requirement or the daily calorific need is the sum of the basal energy demands plus that required for the additional work of the day. The quantity of food which a person will require on a daily basis will be proportional to the total energy requirement of the individual based on factors as described below-

(a) B.M.R. - B.M.R. can be determined from the surface area. An average adult male has a surface area of 1.8 sq. meters and a B.M.R. of about 72 Calories per hour or 40 Calories per sq. meter of body surface per hour while for a female it is 37 calorie per sq meter per hour.

(b) Nature of work- Work involves expenditure of energy, over and above the basal metabolic rate. The following is a rough estimate-

·        Sedentary work-without any muscular effort such as the office workers	20-25% (about 400 Calories)
·        Light work- like household chore	30-40% (700 Calories)
·        Moderate exercise- like walking, playing	50-60% (1,000 Calories)
·        Heavy workout- like weight lifting, HIIT	100% or more (2,000 Calories)

The total energy requirement will be B.M.R. plus these figures.

(c) Allowance for growth. Infants, growing children, pregnant women, lactating mothers, athletes and convalescent patients require at least 50% more food above their actual B.M.R. which is necessary to provide for active growth.

(d) Sleep wake pattern- During waking hours, ingestion of food stimulates metabolism by 5-10%. Similarly physical work done by individual while awake increases calorie expenditure as also calorie requirements.

Thus in an average adult male the total energy requirement during 24 hour period may be obtained as shown in the table below-

8 hours' sleep	(40x1.8) x8=576 Calories (basal)
8 hours' awake, minor work	Basal +30% (i.e. 10% for stimulating action of food+20% for minor activities,) =576 Calories +174 Calories =750 Calories.
8 hours' awake, moderate work	Basal (576 Calories)+1,000 Calories=1,576 Calories
Total	(576+750+1,576) =2,902 (roughly  3,000 Calories)

To provide for the 10% loss in cooking and faulty absorption, the purchased value of the food should have 300 calories more, i.e. total 3,300 Calories. A person doing hard work should receive up to 4,000 Calories.

The average female doing light work needs about 10% less i.e. 2,700 Calories net. A female doing more active work has the same requirement as the average male.

 

The energy requirements of the children are suggested to be as follows:

Age in years	Calories
1-2	1,000
2-3	1,250
3-6	1,550
6-8	1,850
8-10	2,150
10-12	2,550
12-14	2,900

Children of 12 and over require as much food as an adult. Girls between 14 and 18 should have 2,800-3,000 Calories.

For boys of the same age 3,000 to 3,400 Calories are required, a little over the requirements of an adult light worker.

According to Lusk the following are the energy requirements for different age groups in the young people where 10 represent 3,000 Cal or 1 adult unit (also called Human value).

Age	Calorie requirement (in adult units)
0-6	0.5 (i.e. 1,500 C)
6-10	0.7 (i.e. 2,100 C)
10-14	0.83 (i.e. 2,500 C)
Boys 14-20	1.0 (i.e. 3,000 C)
Girls 14-20	0.83 (i.e. 2,500 C)

 

 

Loss during digestion, absorption and cooking

The full calorific value of the purchased food is not physiologically available. During preparation and cooking about 5% of the energy of the food is lost.

A 3% loss takes place due to incomplete absorption of food.

The total loss is thus around 10% so that to obtain 1,000 Calories, the diet should be equivalent to 1,106 Calories.