Zolciak and her husband Kroy Bierman welcomed their newborn son Kash Kade in August, just over a year after giving birth to the couple's first child Kroy Jagger.
The reality star has now revealed to Life & Style that cutting down on meat and dairy has helped her to slim down.
"I've lost 30 pounds," Zolciak told the publication, adding: "I think breast-feeding helped me lose some weight, and I was really busy as soon as I got home with Kash."
She then quipped: "I went straight into filming my spin-off show Don't Be Tardy and I'm sure that helped. I just never sat still."
Zolciak went on to admit that she is still a few pounds shy of her goal weight.
"I'm a size 4 right now, and my goal is to get down to a size 2," she said. "I'm accepting that I'm going to have to hit the gym - my [older] girls laugh and say there's no chance, but I really think I'm going to have to."
The 'Tardy for the Party' singer has two daughters - 15-year-old Brielle and 11-year-old Ariana - from her prior relations.
She married current husband Biermann, an NFL star, at their Roswell, Georgia home in November 2011.