"I put on a normal amount when I was pregnant with Beau, but it took me a year to get back to the weight I'd been before he was born," the singer, 32, who took along Beau on last year's Spice Girls' world tour, tells Britain's Daily Mirror.
"I did it very naturally and slowly," she says. "I went to the gym two or three times a week and ate healthily. I breastfed, so you can't go on stupid strict diets."
Runs and WalksHappy with the results, Bunton is keeping in shape by heading out for a run or walking the dogs she shares with partner Jade Jones – a former singer who's now a chef at a top London hotel.
"It's got to be about balance though, being healthy but not letting it rule your life," she says."When my friends ask me 'round and say, 'Let's get a pizza,' I would hate to be the only person picking at the pepperoni."
Being a mother also helps her state of mind. She calls Beau "my all" – and hints that more children may follow: "[Beau's] so good and funny and loves his cuddles. After having such a wonderful little thing, I can't wait to have another."