> If you take in 500 calories per day and burn 1600, that will fit the "energy burned needs to be >= energy taken in" rule, but you'll still die.

In most developed nations (which, admittedly I assume HN is largely composed of), people have problems with overconsumption as opposed to underconsumption. You're right though, your ideal scenario is energy burned === energy taken in an appropriate weight range for your height and muscular stature.

> Even that basic question is more complicated than you're making it out to be.

It's really, really not.

> I feel like you're trying to grind some axe relating to weight loss here, but in doing so you are obviously oversimplifying the field of nutrition.

I'll repeat what I said in another comment: Maintaining a healthy weight is (or should be, at least) the primary concern of the vast majority of people concerned with their personal nutrition.