Body and Brain
Like any four-year-old little Olivia Tomlinson loves sweets and treats but the youngster is banned from eating them by her worried parents.
Olivia has a genetic disorder that makes her obsessed with food but she needs only half the calories of an average child.
She was born with Prader-Willi Syndrome which means if she wasn't controlled she wouldn't be able to stop eating. It affects around one in 15,000 children in the UK.
The syndrome also causes low muscle tone which means she is allowed only half the amount of calories most children should consume in a day.
Keeping Olivia at a regular weight is a constant battle for parents Karry, 35, and Richard Tomlinson who have to keep her on a strict diet to ensure she doesn't end up obese.
Olivia was finally diagnosed with the syndrome in April after years of uncertainty for her parents. It means she will never be able to lead a fully independent life, because if allowed to, she would eat to the point where it affected her health.
Now Mr Tomlinson, 40, is due to walk the distance of four marathons in four days next month to raise money for the Prader-Willi Syndrome Association, a charity which supports people with the condition and their families and carers.
Speaking at their home in Grenoside, Sheffield, Mrs Tomlinson said: 'It's a condition that often goes unrecognised ~ we slipped through the net for four years and I know of other families in the same boat.
'Often people see someone who is overweight and jump to conclusions that they're greedy and lazy, when syndromes like this show that it's not always the case.'
Mrs Tomlinson first became concerned that Olivia might have Prader-Willi when she was around 18 months old.
She noticed her daughter becoming transfixed by food and began doing some research online.
It means sweets, crisps, chocolate and cake are completely off the menu. Her diet consists of breakfast cereal and milk, a sandwich with no crusts or butter with a yoghurt and fruit, and a proper meal in the evening with plenty of vegetables.
A snack of 50 calories or less mid-morning and mid-afternoon also helps keep her going and she takes part in various exercises such as swimming and trampolining.
Kara, who also works part-time with people with learning disabilities, said: 'She is meticulous in planning her meals out.
'She is thinking soon after her breakfast what she will have for dinner and then the same in the afternoon about what she will have for her tea.
'At the moment we do seem to have it under control, as long as she knows what she is going to eat and when.
'I do know of other stories where this isn't the case though. Parents have resorted to locking cupboard doors to ensure children can't get to the food.
'We do worry about the future and how we will control it as she gets older. But we're determined to protect Olivia from obesity, the health complications and often the ridicule that goes with it.'