Calculating Caloric Requirement of a Person

The caloric intake of an individual must be equal to the calories expended by him over a given period of time, if his body weight is to remain constant. There are four needs which have to be met with by food.

  1. Basal Metabolism: These are calories utilized by an individual who is at complete physical and mental rest. These calories are needed for working of internal body organs and the maintenance of some muscle tone as well. An adult utilizes 1300 to 2000 Calories in 24 hours by basal metabolic activity.
  2. Muscular activity: The calories utilized for muscular activity differs according to the severity of physical work and there is a wide range of variation. Athletes may need 4000 to 5000 or even more Calories per day. Persons doing heavy labor may need upto 8000 Calories per day. The work involving mental activity does not involve any extra expenditure.
  3. Growth and Pregnancy: These conditions and convalescence after a wasting illness are associated with a positive energy balance and more caloric intake is required under these circumstances.
  4. Specific dynamic actions of foods: It has been shown that ingestion of food stimulates metabolism thus increasing the metabolic activity. This increase in metabolic activity seen after ingestion of food is called the specific dynamic action of food. It is most marked with protein foods in which case it may be as high as 30% of the calories ingested in the form of pure proteins. This means that eating a food which contains exclusively proteins will result in an expenditure of 30% of its calories in the form of heath which be of no use to the body. The specific dynamic action of carbohydrates and fats is very low and if these are also eaten along with proteins, the specific dynamic action of this mixed food falls to about 6%. It is apparent therefore that intake of fats and carbohydrates along with proteins is of great benefit to the body system in that relatively much more of the food is metabolized in a useful way.

The significance of the specific dynamic action of foods is that it must be considered while calculating the total number of calories required by an individual. For example, if the numbers of calories required for the above mentioned three factors, i.e. basal metabolism, muscular activity and growth or pregnancy comes to 2000 Cals per day then the number of Cals represented by the specific dynamic action of 6%, then 100/94 x 2000 = 2128 Cals must be ingested to compensate for the loss of 6% of food Cals in the form of body heat. If all the 2000 Cals were to be derived from a pure protein food such as a protein would have to consume 100/70 x 2000 = 2857 Cals per day.

The exact mechanism by which specific dynamic action is produced is not known. Oxidative deamination of amino acids appears to be an important factor in producing this effect. The specific dynamic effect of proteins is not observed when deposition of new proteins is taking place as for example during convalescence after a wasting illness. Thiamine has been found to raise the specific dynamic action of glucose from 4%  to 8%.

From the above mentioned account of different factors influencing the caloric needs of a person it can be seen that it is the muscular activity which is the chief variable factor determining the caloric needs. Thus whereas a man weighing 65 Kg and doing sedentary work needs a daily intake of 2400 Cals, the same person if engaged in a profession requiring active physical work might need 4500 Cals per day or even more.

The following Table shows the number of Calories required by the two sexes at various ages.

Age Year Calories Required Per Day Cals required by females take as percent of male requirement
Male Female
  0 — 1/6 Kg x 120 Kg x 120 100 %
  1/6 — ½ Kg x 110 Kg x 110 100 %
  ½ — 1 Kg x 100 Kg x 100 100 %
  1 — 2 1100 1100 100 %
  2 — 3 1250 1250 100 %
  3 — 4 1400 1400 100 %
  4 — 6 1600 1600 100 %
  6 — 8 2000 2000 100 %
  8 — 10 2200 2200 100 %
  10 — 12 2500 2250 80 %
  12 — 14 2700 2300 85 %
  14 — 16 3000 2400 80 %
  16 — 18 3000 2300 77 %
  18 — 35 2800 2000 71 %
  35 — 55 2600 1850 71 %
  55 — 75 2400 1700 71 %


  1. Kg = Body weight in Kg
  2. Pregnant and lactating women should consume 200 and 1000 Cals respectively in addition to the usual requirements.
  3. These requirements are meant for most of people as they engaged in moderate physical activity.

Conclusions Drawn from Above Table:

The total number of calories required per day goes on increasing with age till a maximum is reached at the age of 14 – 18 in case of boys. After this the requirement falls throughout the later life. This is due partly to a fall in Basal Metabolic Rate with advancing years and partly to a lowered physical activity in older age groups.

The caloric requirements in boys and girls are the same upto the age of 10 years, after which the requirement in case of 10-12 years old girls falls to 90% of that in case of boys in the same age group. The fall in the caloric requirement of females continues in the subsequent age groups. In age groups above 18 year, the caloric requirement of women remain 71% of that of men of the same age. This again is due to greater Basal Metabolic Rate and greater muscular activity in case of men as compared to women.

Children, on weight basis need a greater number of calories than adults. Younger the age, greater is the requirement of calories on body weight basis. This is due to the following reasons.

  • The basal metabolic rate of children is considerably higher, more so at younger groups.
  • A proportion of food material is utilized for growth.
  • Children, as a rule, expend more energy in muscular activity.