You won American Idol at 17. But the first time you tried you were sent home. What made you persist?

The first time when they told me no, I was 15. Maybe the second time round I seemed more determined, or maybe it was just the red scarf I was wearing. I wear that scarf a lot now!

Do nerves get the better of you?

I do get nervous sometimes. Excitement and nerves are the same thing; it's just psychologically how you think about it. I walk out and start singing, and pray that I don't forget the words.

You were schooled at home while out on the road. Never get a bit lonely?

I started to feel it a couple of months ago. I was sitting in my hotel room and I just felt so alone. Even in a group of people I would still feel that way. It was sad, I just wanted to cry.

How do you stay in touch with your family?

Either I'm going to bed or they're waking up, or they're going to bed and I'm waking up, so it's really crazy. But at the same time, I have to sit back and tell myself it could be gone tomorrow.

Feel as if you're missing out on your teens?

I definitely feel like I miss certain things. My brother is 16 and in high school and experiencing all these things right now - but it's a little give and take.

Tell me about that purity ring on your finger

I made the decision when I was 13 to remain pure until I was married. The ring is just a symbol of that and a reminder too. It's a hard thing to refrain from, but I've gone 18 years without, so I guess I can carry on.

Does it ward off men?

Sometimes it really does come in handy. Someone will look at me and I'll say look at my finger. I wear it on my wedding finger for double effect.

And you made the decision at 13, before you should even be thinking about sex ...

It was really my mum and dad. When they sat me down to talk about things, they said that it would be a good thing to wait and they gave me the ring. It wasn't forced; it just made sense to me that when I marry someone I can give my whole heart and not just a piece of it.

Would you expect the same from your boyfriend?

I don't even have a boyfriend. I don't know what I'm missing, you know.

Is religion behind your celibacy?

Yes. I was brought up in a Christian home by a Christian family. My faith is a big part of who I am, how I act, who I hang out with and where I go.

No rebellious streak, then?

I try to stay away from the club scene. I've gone out a couple of times, but I would rather stay at home and read a book because I'm a nerd like that at times. I stay away from situations that would go against my faith.

So you're not a big party animal ...

I've tried alcohol, but I've seen people get drunk and it doesn't look fun. But there are some days I just want to scream at the top of my lungs and say I'm going to go out, go dancing in a club and not care.

Before Idol, you won a plus-size modelling competition. You're no fan of fad diets?

The fact that the word “die” is in diet freaks me out. The obsession about size zero is annoying because it is such a weird perception of perfection. I sometimes just want to say to people, just come with me and drink a milkshake! I'm all about being healthy and I exercise, but I also eat junk food because it tastes so good.

Ever had any body issues?

I had a couple of years ago, wishing I could be like the skinny girls in magazines. The modelling helped me to get over it because I could just stand there and be beautiful in my own skin. But sometimes I want to put a bag over my head.

How do you stay in shape?

I'm obsessed with watching American football. At home, I like to walk up mountain trails with my dog, and, if I ever go to the gym, I like a Spin class.

Any health scares?

Last April I had a vocal cord haemorrhage. It was basically a blister on top of my vocal cords that popped. So when I tried to sing, nothing worked. It was one of the scariest things I've ever gone through. I had to take three weeks of rest and I couldn't talk, sing, cough, sneeze...

Green tea or your GP?

I'm open to both. But if there was an easier, more natural, alternative to surgery, I would try that first.

What makes you happiest?

I love seeing other people happy, like if I did the dishes without my mum asking just because I can. And little kids. And puppies.

Fairy godmother, please change ...

I would make my feet a smaller size.

The album Jordin Sparks is out now

Times recommends

• Think yourself slim with our hypnodiet podcast
• So, what really makes you happy?
• Paparazzi: A flash in the pan