Sequential shift of energy production pathways at the fetal stage and during lifetime.

As eukaryotes, human beings spend their lifetime using two different pathways for energy production: the anaerobic glycolysis pathway and aerobic mitochondria pathway. Energy produced using the glycolysis pathway is utilized for cell division and prompt force of white fiber muscles whereas that produced by the mitochondria pathway is utilized for suppression of cell division and continuous force of red fiber muscles. Herein, it is proposed that there exists a sequential shift of energy production pathways at the fetal stage and during the lifetime. If we introduce this concept in human biology, then it is may be easy to understand the energy requirement characteristics of fetuses, children, adults and aged persons. For example, during childhood the glycolysis pathway is more predominant than the mitochondria pathway in energy production. Reflecting this fact, children grow and extend their height by division of generalized cells of the body. To achieve this, they have to eat meals many times a day (more than three times a day) due to a less efficient energy production rate in the glycolysis pathway. Similarly, the characteristics of adults and aged persons can be well described using this concept.