Human Energy Expenditure (EE) is not stable over a 24-hour period. It varies depending on the time of day, physical activity, the composition of food intake and the quantity of food. The metabolism of one person is very different from that of another. Besides that, our nutrient utilization at the same energy expenditure levels can differ during the day.

The human 24-hour energy expenditure consists of several components. The components can be identified as different stages of the 24-hour energy expenditure. It is possible to measure the different components of 24-hour energy expenditure by allocating individual components to a timeframe. Despite its complexity, the components of human body 24-h EE can be identified and measured with Indirect Calorimetry (IC) equipment, such as the Room Calorimeter or the Omnical.

In this series, we will describe all the EE components. The components we will be covering are:

  1. Sleeping or overnight metabolic rate (SMR / OMR)
  2. Basal metabolic rate or resting metabolic rate (BMR / RMR)
  3. Thermic effect of food or diet induced thermogenesis (TEF / DIT)
  4. Cold-induced thermogenesis (CIT)
  5. Activity energy expenditure or exercise induced thermogenesis (AEE / EIT)


We will publish a new online episode of this series every fortnight.