M.D.
In my experience NO. I had my period every month and I breastfeed my son until he was over 2 years old. He was never on formula at all. He's 4 and would still love to be breastfeed, the other night, he said to me, he wanted milk from my boobies, I told him it's all dried up, he said, put some in them... just had to laugh at that one... He was never underweight. He tall, average, not fat, int he 90% on the charts.