Give that the body can turn carbs into fat and protein into carbs the idea that we can 'only' select one (like we have a favorite or something) is kinda silly. The body will 'out' as it were. It does what it needs to do. It does this cos 100000 years back we had a choice of what the fuck was in front of us or nothing. Cold? No fresh fruit then - berries maybe. Not many animals about - plant protein it is then. 20000 or so years back we started (might have been a little more) agriculture). And so on.
And unless you're an Eskimo or a Zulu (and even then you'd have to be full bore traditional) your diet tends not to be that restricted anymore. The further reality is that people are pretty much dishonest - even with themselves - as to what they eat. They even forget that bag of chips they shared (a family size bad eaten by two being normal) while watching a movie. So you get, all too often, BS like 'I'm carb sensitive'. No you forgot how much SHIT you piled in your mouth. Or didn't weigh it and just guessed and so on.
Unless you're on a mission to Mars and space in the rocket ships hold is limited you don't have to pick one.