Mr Mason, from Essex in England, weighed around 250kg when doctors told him he was in severe health trouble. At age 27, he was wearing 7XL clothes and trousers with a 58-inch (147cm) waist.
His story appeared this week in the UK’s Daily Mail newspaper, when Mr Mason returned back to the UK for a Christmas holiday. He will return to Phuket in a couple of weeks.
The newspaper says that in 2011, Mr Mason was so dangerously obese he was given just five years to live. At 27, and at 250kg, the death sentence finally proved the spur he needed to shed the weight.
A year and a half on, Mr Mason can be proud of the fact he’s shed 147kg, around 100kg of that during his nine months spent training at Tiger.
Mr Mason admitted his weight was the result of his unhealthy lifestyle in England, as he regularly binged on greasy, fried food and meals out while working as a second-hand car salesman, the Daily Mail reported.
He was in poor health due to his weight, which caused breathing trouble, swollen legs and other serious physical problems. After the stark diagnosis, Mr Mason turned to the internet for help.
He discovered Tiger Muay Thai in Phuket, booked a flight, and took the drastic decision to leave his job and move to Thailand.
Despite struggling to even walk around the camp when he first arrived, his training soon began in earnest. Each morning he would run 5.5km on an empty stomach followed by a breakfast of fresh fruit salad, and took part in three or four high-energy Thai boxing sessions every day.
Whereas before he would feast on greasy takeaways and high fat snacks, now a typical dinner was grilled chicken, with vegetables and brown rice.
He told the Mail, “When I was at school I was captain of the basketball team, I played rugby too. When I went to work I got lazy. My weight just crept up on me over the years, I didn’t want to admit to myself that I needed to change my life.
“One day I went to the hospital and they said, “You have got five years to live”. I then went on the internet and found Thai training camp Tiger Muay Thai and then just upped and left. Now I am training people all over the world,” he was quoted as saying.
Mr Mason, who has kept a blog of his time in Thailand, and is now back in the UK for Christmas, said his family and friends cannot believe the change.
“People still don’t recognise me. Mum and dad recognised me at the airport, just, but they had to take a second glance. Some friends here have walked straight past me,” he told the Mail.
But the journey has not been easy for Mr Mason. While he battled with his weight, he also caught a flesh-eating bug and could have lost his leg, and tore his ACL.
He spent three months in hospital in Thailand, and then returned home to the UK for six months, before returning to Tiger.
“It was a struggle to walk 400 metres to begin with and now I am running 10km every morning. It changed my life. I am training four or five times a day.
“I was badly ill in August 2011, I was out of action for three months and had three operations to cut both my legs open and cut the infection out.”
Tiger Muay Thai director Will Elliott said he was “incredibly proud” of Mr Mason and his achievement.
“I think he’s leading the way for quite a few other people who might have been intimidated, shy and too insecure to come here. But now they’ve seen it’s okay, it’s not a hostile environment.
“It’s been pretty inspiring because it hasn’t been easy at all. He had some complications with his leg and was in the hospital and it was pretty serious.
“He was ready to jump on a plane and fly home. He’s had some major setbacks – life threw a lot of curveballs and he adapted. It wasn’t an easy ride, it was tough. But he earned it.”
When Mr Mason first arrived at Tiger, Mr Elliott said, “I was just waiting to see if he was going to put his money where his mouth was. He’s lost more weight than anyone here, ever.
“A lot people make bold claims, but whether they can stick to it with diet and exercise, is another story altogether. I think he surprised everyone.”
“It’s about perseverance – it is early mornings, training even when you’re tired, mental fatigue, and sticking to a diet that may not be that appealing. You have to be disciplined.”
Mr Elliott said he expected Mr Mason’s story in the Daily Mail to have positive flow-on effects for Tiger.
“We always get people that see his blog and come here, and I think this story will add to it. We expect it to yield results for sure.
“He’s been on television in the UK, and been featured in smaller publications, and people find out about him on the internet and on forums. People see it and become inspired – many people have come here because of James.
“He’s part of the family here. He’s a great example, and I think his principles can be applied to life, not just weight loss. You have to persevere, stick to it, overcome adversity.”
Mr Mason is now determined to keep his healthy lifestyle going and has organised a 750-mile bike ride from Phuket to Bangkok in January to raise money for disabled children in the country.
For more information, visit weightlossthailand.com