Another explanation could be that the precursor to grinding in EQ is the urge to do things like searching for edible plants or animal tracks, carving tools, cleaning the home, and other things which have obvious evolutionary benefit.
This has been known to science for at least a century. The slightest glimpse at Wikipedia would have sufficed.
That's not at all the same as saying that more difficult tasks actually consume more sugar, any more than programming must consume caffeine because coffee makes some people more focused on it.
"It does deplete glucose" seems to be in question, doesn't it?
The different is that Jeff gives an argument for why somone would whittle instead of just lazing like a lion or a dog does. Whittling is (slightly) more rewarding, but sleeping is more energy efficient.