Can fast weight loss be healthy if done right?

Fast weight loss is unhealthy because it can slow your metabolism and it will make you start burning muscle (from what I understand so far).

So my question is, Can fast weight loss be healthy if while cutting your calories you still separate to 5-6 meals a day to keep your metabolism up; While also going to the gym everyday working different muscle groups every other day, while still doing a strong aerobic workout every day?