"After I had Isaiah, my goal was to take control of my body again," she shared.
"I gained only 30 pounds, which is the recommended amount, and I exercised throughout my pregnancy ... When I got the OK from my doctor, I started exercising [after giving birth]. Now we box and hike trails, among other things."
"I'm vegan and I love bread, but recently, I started making dinner a breadless meal," she added. "I'll have a bowl of oatmeal for breakfast, and I'll make a sandwich on Ezekiel bread for lunch, but in the evening I'll have protein and vegetables and no bread. When I wake up, my belly is flat!"
Underwood and Fisher, a 35-year-old NHL player, have been together since 2008, and married in July 2010.
The couple welcomed Isaiah on Feb. 27, and the singer recently delighted fans by posting a photo of her son playing a miniature piano.
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