Without the exhausting dance routines she piled on weight and, under strain from a miserable first marriage, she turned to comfort eating.
Within a few years, 5ft 6 Claire went from a size 10 to a 20 and weighed 161⁄2st.
But after losing 6st on a sensible diet and exercise regime, Claire, 31, tied the knot with second hubby Reece Hill, 40, in November and walked down the aisle five sizes smaller – a weight-loss feat she’d achieved in just nine months.
It was an amazing transformation for Claire, who’d suffered a series of personal traumas after leaving Steps in 2001.
'My weight gain was due to a number of things,' she says. 'I left the band, then my marriage broke up in 2005, my parents got divorced and my auntie passed away.
'My ex-husband Mark contributed to the weight gain. He was always telling me to go to the gym and if I asked if I looked alright he’d say, ‘Yeah, but you could lose a few pounds.’ So rather than please him, I kept eating. In the end, we realised we had nothing in common.
'I was 9 1⁄2st when I left Steps and didn’t realise how much being active in the band had kept me slim. I comfort ate for the next four years and I went up to 15st – my thighs spread right out and my stomach was huge.'
Once the weight went on, Claire found it almost impossible to shift. She says: 'It was a vicious circle. I’d look in the mirror and think, ‘I’m disgusting,’ then I’d get depressed and eat another cake.
'I’d have McDonald’s for breakfast, then go out with my sister Gemma for a three-course lunch with cake or ice-cream. I’d have another three-course meal for dinner. And I didn’t do any exercise.'
Claire lost all her confidence. She says: 'I hardly went out because I didn’t want people to see me, but when I did go out people didn’t recognise me because of my size, which was even worse.'
Claire realised how much weight she’d put on when she went to ex-bandmate Faye Tozer’s 30th birthday party in 2005.
She says: 'I’d met Faye’s mum and dad loads of times before and went over to give them a hug. I was chatting away when her dad asked: ‘How do you know Faye?’ I said: ‘I was in the band with her for five years!’ I was mortified.'
Claire finally started dieting in March when she weighed 16 1⁄2st. She had put on a further 1 1⁄2st while pregnant with her son Charlie, born in May 2007.
Now, Claire feels more confident than ever after losing 6st with a sensible regime. 'I started back on a calorie-controlled diet,' she says. “That re-educated me about portion sizes. I cut out junk food and ate healthy meals like fish or chicken with veg for lunch and dinner.'
And when Claire started exercising she saw an even more dramatic change. She adds: 'My muscles became really toned. I started off just walking everywhere. I was so unfit, I couldn’t do much else. Then I experimented with other exercise and found I enjoyed body combat – a mix of a self-defence routines to music. I worked out three times a week for an hour.'
Claire’s now released her own fitness DVD, Five Step Fat Attack, which is set to some of Steps’ biggest hits. She says: 'There’s a warm up, a cool down, aerobics, combat and toning.'
Claire says her husband of three months Reece is thrilled with her new look. The pair first dated in the early days of Steps when Reece worked for the band’s record company.
They rekindled their romance after Claire split from first husband, choreographer and dancer Mark Webb, 34, in 2005. Claire says Reece has never judged her appearance.
She says: 'Reece saw me at my thinnest and he was with me at my biggest, but he’s never told me to slim.'
Now Claire’s excited about the future. 'I look like the old me,' she smiles. 'I’m also working on new music.'
'I don’t ever want to go back to being big. I got lost for a few years, but I’m back!'