system
Given the following post, respond as if you're commenting on Reddit:
human
(LOTR) How does Smaug stay alive?

I'm not too well versed in Middle Earth lore, but what sustains Smaug? A creature of that size would have to intake a substantial amount of food just to live, much less have the energy to fly and breathe fire.
gpt
Dragons are descended from Glaurung, himself most probably a Maia inhabiting the body of a great wurm. It is quite likely that he has some spiritual source of power inherited through Glaurung, or perhaps is himself inhabited by a Maia corrupted to greed and pride. The nature of creatures like the dragons (and even lesser things, like trolls) is never fully explored in the surviving records of the Elder Days.

For another example of spiritual power inherited via a Maia ancestor, see Luthien Tinuviel. Whereas Finrod Felagund, a great King of the Noldor and Calaquendi, was unable to defeat Sauron in a battle of song, Luthien (a Moriquendi, and thus inherently less than her full potential) was able to do so, in part because she was the daughter of Melian the Maia.