Mariah Carey felt like she put on "9,000lbs." when she was pregnant.

The American singer and her husband Nick Cannon are the proud parents of twins Moroccan and Monroe, who turn one at the end of the month.

Mariah piled on weight while she was pregnant and while she knew it was essential for her babies' welfare, she admits it was tough.

"I put on around 70lbs., but if you look at photos of me when I was pregnant, you'd say, 'Wow, she gained 9,000 pounds!'" she laughed to Shape magazine. "A lot of it was water weight because I pretty much had head-to-toe edema, which is very painful."

The 42-year-old singer has now slimmed down, but it was hard work. She realised simply going to the gym more wasn't going to cut it if she wanted a super-toned figure.

"I used to be able to slim down just by exercising more, but that's changed. Since having the babies, I realise that 90 per cent of losing weight is my diet," she explained.

"Today my workout routine is more about getting and staying toned. And for me, that means either taking hour-long walks a few times a week or jumping in the pool three or four days a week to do 45 minutes of aquatic exercises."

Nick has been unwell recently, suffering heart and kidney problems. He is now getting better but Mariah found the ordeal terrifying.

She is looking forward to getting back to normal now her husband is on the mend.

"I've started writing songs for a new album, which I hope will come out in 2012. Getting back in the studio and making music again - which I truly love doing - is the best way to end this crazy year," she enthused.