What I mean by the title is, for example, if we eat mainly protein, does that mean we will have more muscle than fat? (Considering we will be eating nearly zero carbs and relatively lowfat). Maintenance calories of course.
In the opposite case, if we eat mainly carbs, would our body composition have more fat than muscle? Maintenance calories again.
To conclude, does nutrition play a role in body composition? Is there cases showing skinny-fat people having a low protein diet or something along those lines?
Long story short, not really. You can eat protein all day long, if you’re not exercising correctly, you won’t build muscle.
Secondly, body weight has to do with eating above or below your caloric break even point. Eat lower calories, lose weight, be skinny. Eat more calories, gain weight, be fatter. Doesn’t really matter if more calories are coming from healthy sources or unhealthy (to an extent).
In certain circumstances, yes, macros matter, one clear example is if you were to be in a caloric deficit with one diet being high in protein vs another with super low protein, you’ll likely retain more muscle on the high protein diet giving you a different body composition than the low protein diet.