Maintenance of an organism is the collection of processes to stay alive, excluding production processes.
The Dynamic Energy Budget

Dynamic energy budget

The Dynamic Energy Budget theory aims to identify simple quantitative rules for the organization of metabolism of individual organisms that can be understood from basic first principles...

 theory delineates two classes

• Somatic maintenance. This comprises mainly the turnover of structural mass (mainly proteins) and the maintenance of concentration gradients of metabolites across membranes (e.g., counteracting leakage). This is related to maintenance respiration
  Maintenance respiration
  Maintenance respiration refers to metabolism occurring in an organism that is needed to maintain that organism in a healthy, living state...
  
  .
• Maturity maintenance. This comprises the maintenance of defence systems (such as the immune system
  Immune system
  An immune system is a system of biological structures and processes within an organism that protects against disease by identifying and killing pathogens and tumor cells. It detects a wide variety of agents, from viruses to parasitic worms, and needs to distinguish them from the organism's own...
  
  ), the preparation of the body for reproduction.

The theory assumes that maturity maintenance costs can be reduced more easily during starvation than somatic maintenance costs. Under extreme starvation conditions, somatic maintenance costs are paid from structural mass, which causes shrinking.Some organism manage to switch to the turpor state under starvation conditions, and reduce their maintenance costs.