Figure 1

The three big energy consumers in the body use approximately 2,000 kJ/day under resting conditions. Calculation of energy expenditure for the widespread immune system is based on a recent publication that mentions 1,600 kJ/day [4]. Growth-related phenomena in adults are added to this number with 400 kJ/day. A demand reaction for energy-rich fuels (pink circular ring) can be started by one of ‘the big three’ mainly using cytokines and hormones, one of which is interleukin-6 (IL-6). The immune system is activated by external triggers such as infectious agents or self-antigens in misguided autoimmunity and thus is independent of the two other big consumers in starting the demand reaction. The brain is activated by external triggers (for example, stressful life events) or by misguided brain function (for example, major depression), and the brain is independent in starting the re-allocation program. An activated muscle demands energy-rich fuels by releasing muscular factors such as IL-6. The muscle is dependent on brain function to start the energy demand reaction. Whereas immune system activation and growth-related processes happen mainly at night, brain function and muscular function are increased during the day (indicated by the moon and the sun symbols).