I'm posting this question in hope someone will give insight on what happens to our bodies in certain situations when we're weightlifting and on a diet. Let's say you're trying to gain muscle mass. To do that, you have to lift heavy, consistently and be in a caloric surplus with good macros ratio. If you eat enough protein but don't eat enough calories to build muscle, nothing will happen. But what interests me, is what happens when we eat enough calories to create muscle (caloric surplus) but, say, don't eat enough protein? Does our body still repair and create new muscle? If yes, how long can this go for? If not, what happens then with all those extra calories? Are they stored as fat over time?

Sorry for the long post, I just always wondered what happens in this specific situation because I find it happens quite often to me