Jade Heaney, 17, lost three stone in two years

Half of girls and a third of boys have unhealthy concerns over body image

Diet firms are exploiting young people's insecurity to sell quick-fix weight-loss plans which do not work, it was claimed yesterday. The charge came as shocking figures reveal growing pressure on teenagers to change how they look. Half of girls and a third of boys, with an average age of 14, have dieted to change their body shape. More than one in 10 would take pills to alter their appearance, according to Central YMCA research.

An influential all-party group of MPs will begin a landmark inquiry this week into body image in the UK, including the problems of anorexia, obesity and self-harm. They will grill diet companies, psychologists, advertisers and ministers on how to tackle the problem. Jo Swinson, the Lib Dem MP who will chair the inquiry, claimed conflicting messages prompt people to resort to extreme methods in often misguided attempts to match computer-enhanced images. Experts blame a society fixated on appearance, with airbrushing, celebrities and the fashion industry all in the line of fire.

Ms Swinson told The Independent on Sunday: "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.

Ms 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 to the all-party parliamentary group on body image. Other witnesses will include the health food chain Holland & Barrett, the retailer Boots, the British Association of Aesthetic Plastic Surgeons, the British Fashion Council and Shout magazine. Tomorrow 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 that 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 the research fellow Dr Phillippa Diedrichs.

Anxiety and lack of confidence about body image can affect people of all ages in all walks of life, from children who refuse to go to school to adults who will not exercise for fear of how they will be viewed in the gym.

"We are just not celebrating the fact that people can be different shapes and sizes," Ms 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 the idea of 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".

Some progress has been made in recent years. The department store Debenhams has committed to using a wider variety of models, and Boots has reduced the amount of airbrushing in adverts. The Advertising Standards Authority is also credited with taking a tougher line with "overly sexualised" adverts.

The inquiry is being supported by the health and education charity Central YMCA. Its chief executive Rosi Prescott said it is "truly shocking" that one in 10 young boys say they would take steroids to become more muscular, or that one in eight girls would take diet pills to lose weight. She added: "We hope this inquiry will be the catalyst for different industries to recognise their responsibilities and do more to ensure their activities do not contribute to body image anxiety."

Case studies...

Jade Heaney, 17


"In my last year at primary school I was being picked on, so I started comfort eating. I got up to 10 stone. 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 really look like that but they don't understand about airbrushing. It puts a lot of pressure on girls."

Philip Hart, 26


"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. Sport became a bit of a taboo for me. 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


"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. It's hard to educate children, but it needs covering because younger children are developing eating disorders."

Naomi Westland