Swinson said: "In the past 15 years, eating disorders have more than doubled. There is a view that we should tell people they should be really thin because we are getting an obesity problem. But starving ourselves is not a healthy way to lose weight."
In 2009-10, 30 under-10s were admitted to hospital with eating disorders, up from 21 the year before. Nearly a quarter of British women were obese in 2008-09, the highest rate in Europe. One-fifth of British men were overweight, second only to Malta among European countries.
Swinson hit out at weight-loss firms for putting pressure on otherwise healthy people.
"There is very strong evidence that diets don't work. Crucial to the diet industry's ongoing success is people wanting to lose weight and wanting quick fixes. So diet firms rely on people having that lack of body confidence. It will be interesting to find out what proportion of people on Weight Watchers are not clinically obese."
Weight Watchers, which has 1.3 million members worldwide, is due to give evidence. Other witnesses will include health food chain Holland & Barrett, retailer Boots, the British Association of Aesthetic Plastic Surgeons, the British Fashion Council and Shout magazine.
The inquiry will hear from experts from the Centre for Appearance Research at the University of the West of England, University of Westminster and King's College London.
A recent study by the Centre for Appearance Research found one-third of teenagers will not join in a classroom debate for fear of drawing attention to their appearance, and one-fifth stay away from school on days when concerned about how they look. "A significant proportion of girls aged 14 won't leave the house without make-up on," said research fellow Dr Phillippa Diedrichs.
Anxiety about body image can affect people from children who refuse to go to school to non-exercising adults who fear how they will look in the gym.
"We are just not celebrating the fact that people can be different shapes and sizes," Swinson said. "I don't want to blame all celebrities.
"They get criticised too: one minute they are told they are too thin and the next they are too fat."
She backs Britain replicating the US's Fat Talk Free Week, when people stop talking about their bodies - "the stuff that's very self-deprecating ... looking in the mirror and saying hateful things to your body".
IT'S ALL ABOUT BODY IMAGE
Jade Heaney, 17, London
"In my last year at primary school I was being picked on, so I started comfort eating. I got up to 10 stone (63.5kg). When I was 12 I started to control what I ate. I didn't eat much for lunch and stopped eating breakfast. I lost three stone in two years. I became a bit obsessed with losing weight. You pick up any teenage magazine and you see pictures of perfect bodies and you think 'Why can't I be like that?'. People don't understand about airbrushing. It puts a lot of pressure on girls."
Philip Hart, 26, London
"As a kid I wanted to be less skinny. I knew exercise would be a way to achieve this, but I was excluded from the sporty group at school because I am gay and I was bullied because of my sexuality. At university I started exercising alone until I felt a bit more confident and then I joined the gym and sports societies. That gave me lots of confidence but it has become a bit of an obsession. Lots of people take steroids to get the body they want. I'm worried that they are ruining their bodies instead."
Emma Richards, 16, Hampshire
"I had anorexia when I was 12. I was in and out of hospital for two years. It all started with bullying, which knocked my self-esteem and got me worrying there was something wrong with me. In hospital I had cognitive behavioural therapy, which helped me to see that I had the wrong idea about my body. I class myself as 'in recovery'. I don't think you can ever recover, but you can learn to make that part of yourself smaller."
- INDEPENDENT
