I'm a member on atkins.com and Collette the nutritionist there says that a nursing mom needs to stay at a minimum of 50 carbs.

I'm a nursing mom too. I have 3 kids and have been nursing for almost 5 years consecutively. I'm also on induction. I feel AMAZING! So, here's what my instincts say as a mom.

Don't go under 50 until you baby is on solids. (for me this is between 6-8 months old when I start solids on my kids). Then do go as low as you feel good at, and don't loose supply. Even at 20-30 carbs a day (where I'm at) I feel amazing and don't lose supply.

Hope that helps, you can also pop on the forums over there and read it right from the experts.