I'm convinced that this is a science that doesn't exist yet. (Or, at least, isn't established yet.) Sharing information anecdotally is better than not sharing it, but we haven't worked out the principles yet.

I've experienced "starvation mode" and I'm sure as hell not interested in eating that little for any longer than a day or two. I think (with low confidence, though I've seen some physiological just-so stories) that things like exercise and macronutrient breakdown affect whether or not you go into "starvation mode" on a given number of calories. But, regardless, it sucks and people are quite sensible to avoid doing things to their bodies that make them feel like dead dogs.

Edit: I am not a doctor, but the other standard thing to get checked is testosterone levels.