Metabolism is the process by which human body converts foods into mechanical work and heat. To do useful work body obtains energy from the food,. A large part of this the energy is converted into heat and the rest is used to do muscular work. The percentage of total energy available to perform work ranges from about 10 percent to 25 percent of the total energy available in the food.
The energy utilized by the body at rest for maintaining the internal body functions is about 1200 kilo calories per day. This is called the basic metabolic rate or BMR. Additional energy is required by body to do additional work. These additional activities can be divides in two categories. One is the minimal activity that people perform irrespective of their profession. These activities are called leisure activities. The typical energy required for BMR plus leisure activities is about 2500 kilo calories per day.
Second type of activities is called the occupational activities. The energy required for occupational activities is heavily dependent on the nature of occupation. Assuming a work of 8 hours a day, the typical energy requirements for some common types of occupation is as follows:
Seated office work: 800 kilo calories per day
Light assembly work: 1680 kilo calories per day
Ocean fish netting: 800 kilo calories per day
Lumberjacking: 6000 kilo calories per day