I would say if one is on a low carb diet, protein could be increased. But not by much...
If one is consuming adequate carbs, then high protein intake is not even necessary, as carbs are protein sparing. I'll then go to the lower end of the scale, 1,2g/kg...
Currently I'm getting in below that! 100-110g a day, and my carbs are about 250g, and I haven't felt any negative effects as yet. Note that I am around 12% bodyfat now.
I would say once you go below 8% as a natty, you start to risk muscle loss. And as I just want to get to sub 10%, I don't think there is need to worry.
I've read that only once you get into the essential bodyfat (4-5%) range, your body will only then start to eat away muscle.
Yes, muscle is very metabolically active, but as long as you have a stored energy source (fat) and immediate energy source (carbs), your body won't catabolize it.
I've stopped overanalyzing nutrition and just sticking to the basics.
That's what its all about:
Calories in < Calories out
Adequate protein (1,2-1,6g/kg), fat (0,3-0,5g/kg), carb (rest of calories) intake.
Also, note that these calories do not come from junk, although it can be included, but it comes from nutrient dense food (not necessarily traditional bodybuilding foods)