Honestly?

I would rather be 140 wearing a size 6, than 130 wearing a size 6. Why?

Muscle weighs more. I would rather be a very toned 140 pounds and looking healthy than 130 and looking rather thin. I was once at 120 and very bulimic and very unhealthy looking. Gaunt would be a good word for my looks.

Would 5 pounds of muscle make that much difference on your small frame? Maybe your doctor and nutritionist are thinking that way as well. Muscle does weigh more than fatty tissue. Would you rather weight a bit more if you could have nice firm muscles?

I know I would

Best of luck in what you decide.