Fig. 2.

The second model proposes that thrifty and profligate genes are regulated by two independent mechanisms activated by states of energy surplus (orex-genergostat) or depletion (anorex-energostat). For example, in a state of negative energy balance (Famine) the decrease in energy availability induces an activation (solid lines) of the anorex-energostat and an inhibition (dotted lines) of the orex-genergostat. The sensor would then activate the catabolic genes (profligate) and inhibit the anabolic (thrifty) ones to exert their catabolic action. A feedback mechanism between these genes can be envisaged to modulate their actions (double arrow lines). The system in a state of positive energy balance (Feast) would operate with a similar but opposite mechanism.