Despite her long legs and slim physique, the blonde star said she is now hitting the gym in a bid to tone up and feel more confident.
'I was a size 6 from all the dancing in Girls Aloud and I must have been under eight stone and that is not a healthy weight,' admitted the star.
But although Harding is just one dress size above her Girls Aloud days, it seems she isn't happy with her body.
'Now I am a flabby size 8 and my things and bum need toning.'
The 32-year-old is currently loved up with DJ Mark Foster, and says she is looking forward to having children in the next few years.
The star had a well documented struggle with partying and rehab in her 20s, but she now says that is behind her and she's looking forward to the future.
'My twenties were definitely for break-ups and handovers and it's a real learning curve. I think your twenties are the most dramatic years of your life.'
Sarah will perform an acoustic set on Thursday 20 March in aid of Street Child.