If calorie restriction is causing those side effects, it is an indicator that the person is "doing it wrong" by either restricting their intake far more than is

If calorie restriction is causing those side effects, it is an indicator that the person is "doing it wrong" by either restricting their intake far more than is healthy or more likely their diet is very sub optimal (eg, 100% carbs causing blood sugar to spike and then crash when they "run out" of calories). These are problems of application which are easy to fix with a food journal and perhaps a bit of research, not really a great argument against calorie restrictions effectiveness.