Is "Allostasis" The Brain's Essential Function?

A paper just published in Nature Human Behaviour makes some big claims about the brain. It's called Evidence for a large-scale brain system supporting allostasis and interoception in humans, but how much is evidence and how much is speculation? The authors, Ian R. Kleckner and colleagues of Northeastern University, argue that a core function of the brain is allostasis, which they define as the process by which the brain "efficiently maintains energy regulation in the body". Allostasis entails "anticipating the body’s energy needs [and] preparing to meet those needs before they arise." Kleckner et al. point to "physical movements to cool the body’s temperature before it gets too hot" as one example of allostasis. A concept closely related to allostasis is interoception, the process by which the brain receives information about the body's internal state from sensory nerves inside the body.