I've always said, calories still matter, but they aren't the same.
You can still eat too many "calories" of nutritionally dense foods, but it is a lot harder.
A calorie is a unit of heat.
Humans are not bomb calorimeters.
A bomb calorimeter burns food and measures how much heat comes off.
Your body doesn’t burn food in a metal box.
It digests it.
Absorbs it.
Stores it.
Uses it to build tissue.
Turns some of it into hormones, enzymes, neurotransmitters and cell membranes.
100 calories of steak and 100 calories of jelly beans may contain the same amount of energy on paper.
That doesn’t mean your body responds to them in the same way.
One tends to fill you up.
One makes it easy to keep eating.
One provides protein, iron, zinc and B vitamins.
One provides mostly sugar.
The calorie number is the same.
The biological response is not.
That’s why reducing nutrition to “calories in, calories out” has always felt too simplistic to me.