Teenager Dionne Martyn says she has felt the benefits of taking more exercise and eating healthy food.
The 13-year-old from Abertillery took part in one of the pilot projects of a £1.4m scheme aimed at helping children in Wales manage their weight.
Around 2,000 children, aged seven to 13, and their families will attend free 10-week health courses.
Dionne said the course was fun and she was now eating healthy foods that she previously would not have touched.
"You do games rather than proper workouts. Doing more exercise means you get fitter and they tell you the right portion sizes [of food] and what's good and what isn't so good," she said.
"I eat fish - tuna steaks. I don't normally like fish but I do eat them."
Although her friends had questioned why she had taken part in the programme, Dionne said she had really enjoyed it.
"They don't think there's anything wrong with me - they just think I'm nuts going on it!"
The Mend programme - short for Mind, Exercise, Nutrition... Do It! - focuses on "weight management skills" rather than on losing weight.
Dionne's mother Ellen Anstee said this approach had not only helped her daughter get fitter, but had given her confidence too.
"Since we started the Mend programme, she's been far more active, far more confident, far more happy in herself. There's been massive changes in her," she said.
"I was surprised because when we were first offered the Mend course, I didn't know if she would stick to it because it was a group and she has always been worried about those things.
"For her to stick to it and to have come out like this at the end has been fantastic."
Ms Anstee said the benefits of the course would stay with her daughter for life.
"I think it's very important that they start quite young, and the good thing about Mend is that Dionne has had a nutritional input," she said.
"It will carry her on through life because I'm not always going to be there cooking her meals.
"I think it's important that they know what they're eating and understand how important it is to be active."