It is complex, precise dietary requirements vary person to person (even mouse to mouse but less for lab strains). As a generality women have lower caloric requirements, men higher. Age, height, weight, activity level, genetics, etc all have impacts.

The timeline of caloric restriction matters. Muscle breakdown occurs first because muscles store glycogen which is a much faster energy source than fat. Fat breakdown can go on for longer as it has a higher density of energy. Simple short-term reduction in calories thus results in muscle before fat. Higher protein intake mitigates or prevents muscle loss in longer-term diets compared to lower protein intake as the muscle cells are used to process/use the protein. Exercise is the best at keeping or growing muscle as it turns them from energy providers to energy users.