At the age of 15, Nathan Hewitt weighed 23 stone and was branded one of Britain's most obese schoolchildren. But look at him now!
Eight years on, Nathan has grown up and slimmed down – losing half of his body weight. And he's now so trim he is making a living as a weight loss coach, inspiring others to follow his example.
As a schoolboy, Nathan, from Merthyr Tydfil, in South Wales, ballooned after binging on fast food and sitting around playing video games.
But after being ridiculed on a roller coaster ride at Alton Towers, he was shamed into losing 12st.
Now Nathan wants to help the nation's obese kids get in shape and the Welsh Government has given him financial support to get his business up and running with a Young Entrepreneur's Business Grant.
And in an ironic twist, some of his first clients are the classroom bullies who made his life hell when he was the fattest boy in school.
Nathan said: "I've been there, I know how it feels to be massive - you only have to look at my old photographs to see I was huge.
"But I can use my experience to encourage other overweight children to slim down and change to healthy lifestyles."
Nathan's turning point came during a family trip to Alton Towers where he couldn't wait to go on their latest ride. But the attendants couldn't pull the safety bar over him and he had to walk off while people in the queue sniggered and poked fun.
He said: "I knew at that moment I had to change my life for good - my weight was making me miserable.
"I'd put up with years of bullying in school and I took comfort in the only thing I knew and that was food. It was a vicious circle."
But after going on a healthy diet and exercising Nathan more than halved his body weight to get to 11st.
He had surgery at 19 to get rid of the excess folds of skin he was left with - but since then he has not looked back.
He said: "A lot of obese children don't think they can make the changes they need to lose weight - but I'm there to show them they can.
"It's hard but it is do-able and I'm the example of that.
"My life has changed in so many ways - I'm more confident, healthier, fitter. I really feel like a different person to when I was 15 and over 300lbs."
Nathan is launching the first of his weight loss seminars 'Try This For Size: The Weight Loss Breakthrough Programme' in Merthyr Tydfil which has a problem with child obesity.
He was given a £6,000 grant and the services of a mentor to help him set up as a weight loss coach.