if u are in a low calorie diet for too long, u get something called diet fatigue. this also slows down ur metabolism. for ex, if someone has been eating at 2000kcal for several months and now he is in diet fatigue and his metabolism is slowed down, he wont be burning the same amount of kcals despite working out and doing cardio. in this case, do you think this person should up his calories a little? his goal is to have a light bodyweight so that he can still train statics.