source: http://www.jissn.com/content/4/1/8
Also, this is one of my favorite quotes on the matter from an intelligent poster:
I think these guidelines are geared more toward atheletes working out twice a day, 5 days a week, maybe even more, with very high intensity. So I would say their protein demands are bigger.
But if you look at the average gym rat, working out 3/4 times a week, for 45min - 1 hour a day, 1,2g/kg is more than enough I would think. I would say if one adds cardio to the equation I would maybe increase it to 1,5g/kg. But either way I think 1,2g/kg is a good starting point.
I've been eating below 1g/lb protein for a while now and fasting 2x a week and I haven't lost any muscle. And I've been cutting. Lost 6kg so far and I'm now around 12% bodyfat.
I've read John Barban and Brad Pilon stating you only start losing muscle when you are near essential bodyfat levels (3-5%), until then, your body has more than enough fat to give your body energy.