The 13-year-old weighed 106kg, his body was 48% fat, and alarm bells rang when he thought he was going to die doing simple activities.
Tavita's deteriorating health was noted during a parent-teacher interview and, given his mother died of a heart attack five years ago, his father Tony Mamea decided to enrol Tavita in a new youth fitness programme for 10- to 13-year-olds at Creative Conditioning in Dunedin.
Since then, Tavita's heart rate has dropped from 170 beats per minute doing gentle exercise to 130 beats per minute during strenuous exercise.
He has also lost 12kg, 22cm from his waist measurement and is now at 32% body fat.
A healthy male body contains 15%-20% fat and women 18%-24%.
"I used to think I was going to die just walking up stairs. But now it's easy. I used to avoid the stairs - now I run up them," Tavita said.
"It's changed my life a lot. I used to sit around at school watching my friends outside. Now I'm out there with them, running around - and keeping up with them."
While he was excited about his weight loss, he was also proud of some of the achievements he had made in the past six months.
In September, he walked the Moro Half Marathon - something he never dreamed he could achieve.
"It was hard work, but when I got to the end, I was surprised. I didn't think I would finish it. Next year, I want to run it."
Tavita said he goes kayaking with his father most weekends and is now learning to ride a bike.
"I'm a bit wobbly still, but I'm getting there," he said.
Tavita is chipping away at his body-fat percentage, and his father continues to pummel the boxing bag in the corner during Tavita's sessions to support him and improve his own health.
Creative Conditioning director Gary Dawkins said the youth programme was established because of an increasing number of children were growing up on a couch watching TV as well as living on poor diets.
As well as interactive one-on-one body-weight exercises, kick boxing and circuit drills, members are given recipes to help change their diet.
Mr Dawkins was delighted with Tavita's progress so far, and believed the exercise and diet regime would take Tavita a long way towards his goal of running the half marathon next year.
"I feel like I've got a life now," Tavita said.
"There's so much out there to do."
