I'd say it's the liver (or some other part of the gut-brain i.e. autonomic nervous system) that is lazy.

If you've ever tried a caloric deficit you know something within does not like it and will complain constantly so long as it's happening.

The brain must actively supress this which is tyring.

If anything the brain is not lazy, it just tries to be efficient. Oh, and the heart is all the opposite. it won't ever give up until it really biophysicall cannot go on.