I've been making dosa lately and was wondering if you could make the batter using only soaked urad dal (black lentils)? Or, do you have to include soaked rice, as well?  I am diabetic, so I am trying to make dosa batter more "diabetic-friendly," because I love them so much!  If not, what's the smallest amount of rice you can use?  Currently, I use 3 cups rice and 1 cup urad dal. I am using brown basmati rice, because it's a little better, carb-wise.  Thanks in advance for answers! 
Yes, you can make dosa without rice! I am very health-conscious and one day tried making dosa without rice and it worked very well. Moreover, this doesn't even require fermentation. Just soak urad dal for couple of hours and grind it into a smooth paste. Make the batter as thin as regular dosa batter and enjoy :) 