You have to be careful though, without fat the body will not allow your breasts to develop and you risk a number of health complications.
The way the body works is that it will delay or halt breast development until it believes the environment favourable to bear children and for them to survive, in cis women the body can also stop a girl from having her periods for the same reasons. It's a natural defence and energy conservation mechanism, from an evolutionary standpoint if there isn't enough food and energy to go around then is very doubtful a child can be successfully carried to term and fed throughout it's childhood so why waste some of that precious energy on boobs.
When I got diagnosed with Type 1 diabetes my body had burned all the fat (I could not even sit down because it hurt so bad when my bones rested on chairs), also all my muscle was gone since my body had cannibalized itself for energy, I was probably around 75kg and I looked horrible, like a walking skeleton. I'd say currently my ideal weight is probably around 81-82kg which sounds high but that's just my build and bone structure, everyone is different.
