Posted: 22/01/2015 at 07:03
Yes agree it's the composition that matters not the BMI. % body fat is a much better indicator but hard to measure reliably, whereas BMI is of limited use but is an easy reference to measure for anyone. If you know your protein intake is sufficient and you're not seeing or feeling significant loss of muscle then you can be reasonably confident that you're retaining muscle mass.
If I go by my scales at home - I've had different ones give similar results but values are only really useful for individual trends as the absolute numbers must be taken with a large pinch of salt - then I still have visible belly fat (ie enough to obscure abs) at 8-10% BF, it's only when I get down to around 7% that I look lean there, which corresponds to about 65kg for me on numerous occasions.
I tend to only hover around that racing weight for a few weeks at a time leading up to target races, I like the occasional cake, wine, chocolate, curry and pizza too much to stay that lean all year round. I just stay within a range that I know I can get back to that level within a few weeks of good training+nutrition if I have a goal coming up.