You're thinking it wrong. It doesn't lose points, but it loses stages. And this is also not permanent. Now, when you use Superpower, your Attack and Defense each drop by one stage. Raising and dropping stages will multiply the original stat by a certain factor, based on what stage it is.
Stages for Attack, Defense, Special Attack, Special Defense, Speed
Stages for Evasion and Accuracy
You can get rid of stat lowering by simply switching out, your letting your Pokemon hold the one time use item White Herb.