Energy is defined as the potential to do work that is obtained from the oxidation of carbohydrates, proteins and lipids present in our diet. It is also obtained from the chemical reactions in the body. The oxidation of food may be either in the presence of oxygen or in its absence for energy purpose. There is a misunderstanding that the people consider energy as good and kilocalorie as a bad thing. Both are the same things. Kilocalorie is the measuring unit for energy. About half of the daily energy need is fulfilled by the controlled oxidation of carbohydrates, proteins and fats in the diet. In this article, the discussion will be about the energy consumption, its expenditure and the factors affecting the energy needs.

Energy consumption:  

Half of the energy obtained from the food oxidation of daily diet intake is consumed in the following (most of it is used in the self-maintenance):

  • Energy release from glucose and fatty acid reactions
  • Wastes elimination from body through kidneys
  • For the synthesis of new proteins for growth and repair
  • In thermoregulation; maintenance of body temperature at 37 centigrade
  • Maintenance of the fluid electrolyte balance
  • Contraction of muscles in breathing
  • Contraction of cardiac muscles
  • The remaining half of the energy produced is used for the daily muscle activity and for special purposes such as pregnancy, growth and lactation.
  • Over short term consuming high and lower amounts of energy is harmless but the condition not remains the same for longer period.

High energy condition:

When you consume high energy diet, the energy exceeding your energy needs is stored in the form of either glycogen or fat in the body.

Low energy condition:

When you are not getting the enough calories from your daily diet or you may suffer from the starvation, you are gradually creeping towards the muscle loss, stunting, wasting and protein energy malnutrition.

Energy expenditure:

Human body requires energy for the performance of all functions. It is needed for:

  • Maintenance of body temperature.
  • Continuous activities of heart, lungs, kidneys etc.
  • Repair of the tissues and growth.

Basal Metabolic Rate (BMR):

Basal metabolic rate is the minimum amount of energy requires to keep the body functions run at the rest.  It may be the amount of energy needed to keep yourself alive at rest or during sleeping when you are in the zone of thermal neutrality and the digestion and absorption of the last food has been ceased. It is the relation of the muscle mass and surface area of the body from which the heat is lost.

  • BMR varies with the age, sex, disease, weight and other factors. Children have higher BMR than adults.
  • As the BMR decreases with age so, the weight gain is easier than the weight loss in adult life as the production of thyroid secretions promoting the metabolic activity is decreased. It usually decreases by the rate of about 1% per year after age 25.
  • BMR rises with the weight. In females due to less muscle portion and increased fat mass, the BMR is lower as compared to males as they have greater muscle mass portion.
  • In case of females, the BMR is about 1500 kcal as compared to males who require 1700 kcal of energy.
  • BMR is higher in diseased condition. For example, when you are suffering from fever it increases by 10% for every degree centigrade rise in body temperature.

Energy needs:

Energy is provided through the oxidation of food components that are the carbohydrates, proteins and lipids. The energy must be supplied for the BMR and the daily activities so that you may not suffer from the energy shortage.

Factors affecting BMR:

Many factors affect the BMR. These are:

  • Body weight
  • Age
  • Specific conditions (such as pregnancy and lactation)
  • Activity

Body weight:

Body weight influences the BMR. It is lower for obese persons at rest. But during activity, use of energy is proportional to body weight. Women use less energy at rest.


The requirement of energy for children and adolescents is higher in proportional to their weight as compared to adults. Older adults use less energy than the adults and young people.

Pregnancy and lactation:

In such conditions energy requirement for women is increased e.g in pregnancy by 200 kcal extra and in case of lactating lady ratio is 500 kcal extra.


More energy is required during activity than at rest.


So, in a nutshell, energy is the body requirement to keep our life thriving. It is obtained from the food oxidation and is consumed in many body processes. We should take the balanced and checked diet for optimal energy gain.

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