You're co-presenting Supersize vs Superskinny Me on Channel 4 and looking very trim - do you have to work hard to stay in shape?

I've actually lost 2st since series one. Back then I was 11st and about size 14. It was the result of being lazy, stuck in a rut and unhappy. I was comfort eating. Now I'm 9st and size 10-12. I'm slimmer and also happier.

How did you do it?

It's a mental battle; you have to master your mind before anything else. It was having hypnotherapy in series one that really made me aware that I didn't want to be the person I was. So I changed what I was eating and I exercised.

And you've managed to keep it up?

I try to exercise at least three times a week. I did a two-week regimen with the fitness expert Matt Roberts when I was losing weight. It was a red-carpet-ready celebrity routine. An hour and a half of exercise a day and a strict diet. It was intensive and aerobic. In 14 days I lost 8lb in fat [and] put on 5lb in muscle.

Sounds very Hollywood ... didn't you go over to Los Angeles for the new series?

From the second I touched down I spent half the time totally shocked and half the time totally sucked in by it. They are obsessed with how they look. They're kind of split into two groups. Half the women are size zero, have surgery up to the eyeballs and look really weird, and the other half are just naturally beautiful and exercise a hell of a lot.

How did you fit in?

When I asked people on the street whether I did, they said: “No, you need to lose 20lb.” One celebrity trainer told me I had “carb-face”!

Carb-face?

She asked if I'd eaten bread or pasta the night before and then said: “Your face is all puffed up because you've got water retention.” She said all us Brits have it.

You've revealed a lot about yourself on TV, especially on the Sex Education Programme earlier this year. Anything you wouldn't do?

I draw the line at anything dangerous or too intrusive. A really good friend of mine in TV production rang me recently and asked if I'd be willing to try crack and heroin as a piece of “immersive journalism”. My response was: “Are you out of your mind?”

So, not too much of a dark side, then?

No. I don't have any worrying addictions apart from food and shopping. But food is a constant battle. Like any addict, I sometimes fall off the wagon and have a whole packet of biscuits. But I always get back on again.

What's your biggest health fear?

My grandmother killed herself and there is a depressive streak running through my family. So my biggest fear is that I'll end up in some One Flew Over the Cuckoo's Nest situation. I've suffered from depression in the past but it has always been a response to a specific event.

What happened?

I was 21 and had an ectopic pregnancy. I thought I was going to die. It was very traumatic, and I suffered from anxiety and panic attacks afterwards.

Get any help?

Absolutely. I got help after the pregnancy and again after being robbed by two men in my hotel room in the South of France a few years ago. I'm a massive believer in psychotherapy. Everybody in the world should have it.

Do you find any solace in anything religious or spiritual?

My mother is an RE teacher and my dad is a canon. But, no, I'm not religious myself. I don't believe in God; more in a creative force.

What gets your goat?

I'm a hugely confrontational and passionate person so I think it's apathy that really makes me mad. And rudeness. And bad service. It's something to do with how I was brought up.

Fairy godmother, please change ...

I'd make my bust a bit smaller. I've always had massive knockers, but they're a pain. They get in the way and they make you look fatter than you are. I mean, really, who wants 32F boobs?

The new series of Supersize vs Superskinny starts on Channel Four, January 20, 8pm

Explore Women

• Fashion

• Beauty

• Diet & Fitness

• Relationships

• Families

• Celebrity

• The Way We Live

• Horoscopes

Times recommends

• How I lost the gift of joy for a while
• How to get Coleen Rooney's post-baby body
• The A-Z of winter style rules