I conceived dd#2 when my bodyfat was 14%, not sure what it was with dd#1, but it certainly was less than 20%. While breastfeeding dd#1 my body fat got as low as 11% (which was too skinny). Never had a problem with my milk supply and had no trouble getting pregnant with dd#2. With my build 20% body fat looks dumpy rather than voluptuous. I am following the Schwarzbein Principle diet, which is not ketogenic (although I'm sure sometimes I slip into ketosis anyway). I eat close to 100g carbs/day.

Jen