Boobage and muscle preservation

Oishii

I'm at a weight and body fat % where my face is slim enough to make my eyes look big and cute (seriously, I worked out that's why I like this weight) and I still have approx. B cups that I don't want any smaller. From past experience, very little of what I have up top is 'breast tissue', it is nearly all fat, so it is a major source of fat loss

However, I would like to be fitter, meaning being able to do more with my body. I want to be able to run further, lift more, improve my heart health and bone density.

So, here's what I was pondering: if resistance training helps preserve muscle mass when at a deficit or maintenance, that means fat loss, and therefore boob loss, if my body requires more energy than I provide it with at the time. So... To get fitter and not lose the boobs, I'd have to eat to at least maintain, if not gain, right? Or avoid resistance training if losing?

Oh, and please don't worry about my damaging my metabolism: my maintenance kcals are above 2500 at 58kg (128lb), so it wouldn't matter if they went down a little.