lol It feels insane sometimes..but it's not unhealthy! Theres tons of research..much better than fad diets.
It's technically called the "Johnson Up Day Down Day diet" you can google if you're really interested.
It's basically alternate days..eating a normal healthy diet on your "up day" (even a tad of junk food which is what I end up doing) and then on your "down day" eating 500 calories or less. It's compared to alternate day fasting which is also really healthy for you. I'm not sure about doing it with breastfeeding though, because I'd hate for you to cut cals and affect your supply.
Since you're only cutting cals for one day (or fasting if you're ready for it..its HARD) it doesn't hurt your metabolism. It has great health benefits including helping asthma, detox, more energy because your body is cleaning our your system instead of using its reserves to digest food, etc etc.
Google explains it better. but it works, and I'm healthy..altho I had down days where I felt horrible (detox).
I lost 35 lbs in 5 months before I got pregnant with Abbey..then I lost 30 lbs again after Abbey. I'm def doing it after the twins!