The singer recalls her battle with anorexia and weight dysmorphia in her new autobiography All of Me, which is being serialised in The Sun.
Richards wrote that when she first joined the pop group in the mid-1990s along with Lisa Scott-Lee, Faye Tozer, Lee Latchford-Evans and Ian 'H' Watkins, she was told to lose weight despite only being a size 10.
"Before I got into the band I was made to promise I would lose weight. I was ten stone at the time - not big, especially as I'm 5ft 6in. It was the first time I was conscious that perhaps I was bigger than the other girls but I didn't dwell on it.
"I had no idea those comments about my weight would come to haunt me during my time in Steps. Soon after we got signed, we went to Marbella in Spain to shoot the video for '5, 6, 7, 8'. Because the shoot was on the beach, they wanted the girls to wear bikinis. I panicked straightaway.
"There was no way I wanted to expose my hips and bum in bikini bottoms, so I asked for a bikini that had one of those matching miniskirts. I ended up wearing an orange bikini with matching mini for the video."
The star said that she dropped to as low as eight stone at one point during her time with Steps and would often throw up her meals in fear of putting on weight.
"I was young, in the spotlight and under pressure - not only to perform but to look a certain way. Controlling your food intake gives you the sense you're in control of life," she wrote.
"I remember reading about anorexia when I was just 11. I didn't know what anorexia was then, but I remembered the word and, years later, I was to understand only too well what it meant."
She added: "When we broke for lunch we were all taken to a burger joint, so I had no choice but to sit there and eat a burger with everyone else.
"As soon as I'd finished it, I started panicking. I rushed back to where we were filming, found the toilets and stuck my fingers down my throat to try to make myself throw up. All I could think was, 'I have to get this out. I can't get on stage with this inside me'.
"I felt totally repulsed by the greasy burger I'd just swallowed. I must have been in the toilet for ages because the burger just wouldn't come up.
"Eventually Lee came in and said, 'Are you all right, Claire?' I think he suspected what I was up to, but I just made out I didn't feel very well. As soon as I'd been sick I went back to work as if nothing had happened."
Richards recently said that she is "proud" to now be a size 16 and that the group's recent reformation would not "brainwash" her into losing weight again.