Table 5.
System/organ | Energy expenditure per day (kJ/day) |
---|---|
Muscle at restb | 2,500 |
Central nervous system (brain and spinal cord) | 2,500 |
Immune system in a quiescent statec | 1.600 |
Liverd (including immune cell activity) | 1,600 |
Heartb | 1,200 |
Gastrointestinal tract (including gut immune system, without liver, kidney, spleen)d | 620 |
Kidneys | 600 |
Spleen (erythrocytes plus leukocytes; 90% anaerobic) | 480 |
Lungsd (including lung immune system) | 400 |
Skind (including skin immune system) | 100 |
a10,000 kJ = 2,388 kcal. bActivated muscle has a much higher metabolic rate: for example, a Tour de France bicyclist needs approximately 30,000 kJ/day, which is 20,000 kJ more than under sedentary conditions. The 20,000 kJ are used predominantly by the muscles and also the heart. At the upper limit of gastrointestinal resorption, the total body daily uptake (absorptive capacity in the gut) is 20,000 kJ/day. cModerate activation of the immune system increases daily energy needs to approximately 2,100 kJ/day, and strong activation increases the daily need to 3,000 kJ/day. dEnergy need is difficult to estimate independent of the immune system in some organs.