> models who need to be a certain shape; football players who need to be heavy so they don't get lifted off their feet by their competitors; or dancers who need to be light so that they can get lifted off their feet by their partners.

I have never seen or heard about a professional diet based on calorie counting.

Every single diet is based on a prescription of nutrient types and quantities, when it's not a detailed prescription of food types and quantities. And the diets that end-up working are all revised several times after controlling by patient's health.