Energy Consumption Of The Human Body

Donish Khan
December 13, 2012

Submitted as coursework for PH240, Stanford University, Fall 2012


Fig. 1: A flowchart of the metabolic summary of the human body. (Source: Wikimedia Commons)

In this day and age, new and exciting forms of energy have been researched to power our latest technology. Tons of resources and research have been spent on understanding how today's latest gadgets and machines consume energy. Yet, despite all of this state of the art research, we seem to forget that the human body itself is actually a machine and food is its energy source. Like any other sophisticated device flooding our mainstream, the human body requires and consume energy in a similar way and understanding its inner-workings is essential.

The Human Body

The human body carries out its main functions by consuming food and turning it into usable energy. Immediate energy is supplied to the body in the form of adenosine triphosphate (ATP). Since ATP is the primary source of energy for every body function, other stored energy is used to replenish ATP. There are only small amounts of ATP in the body so it is necessary to have sufficient energy stores for backup. [1] The amount of daily energy each body requires depends on an individuals daily energy consumption and metabolic energy requirements which can be estimated by body weight and activity level.

The basic energy consumption of the human body is 4 kJ/kilogram of body weight and daily hour so to calculate an individuals basic energy consumption:

Total Energy Consumption = Body weight (Kg) × 4 KJ × 24 hours/day / 4.18 kJ (1)

The total energy consumption value is divided by 4.18 kJ in order to convert the value into kilocalories (1 kcal = 4.18 kJ). This calculation represents daily energy consumption. Excess food intake that is not used as energy can be stored in the body as fat. Excessive fat storage can lead to a high body mass index. Body mass index (BMI) indicates a persons body fat and is determined by an individuals height and weight. [2] The normal suggested BMI in adults ranges between 19 and 24. A high BMI can potentially lead to illness or health complications. [3] In order to have an ideal BMI, an individuals energy intake must not exceed the energy burned on a regular basis. The amount of energy exerted depends on activity level.

BMI = Body Weight (kg) / Height (m) × Height (m) (2)


Energy, measured in kilocalories, is a representation of capacity to do work and that energy is obtained through food. Carbohydrates, protein, and fat acquired from foods provide ATP, immediate energy. [2] If the energy from food is not utilized through activity, it is stored in the body and overtime can lead to a high body mass index. Having a high BMI may lead to obesity and other illness.

© Donish Khan. The author grants permission to copy, distribute and display this work in unaltered form, with attribution to the author, for noncommercial purposes only. All other rights, including commercial rights, are reserved to the author.


[1] M. Williams, Nutrition for Health, Fitness and Sport, 8th Ed. (McGraw-Hill, 2006).

[2] "Dietary Guidelines for Americans 2010," U.S. Department of Agriculture, December 2010.

[3] L. A. Ferrera, Focus on Body Mass Index And Health Research (Nova Publishers, 2006).