A high-tech camera "cut open" Stewart's torso
By Sarah Wood
Series producer, BBC Three
Earlier this year a good night out for Stewart Burton might have started on a Saturday afternoon in his home town of Brighton and could easily have carried on for 18 hours, well into Sunday.
Stewart, 25, would get through up to 60 cigarettes, down nine bottles of beer, followed by several shots and more beer. He would also dabble in drugs.
That was a good night out for Stewart - but he was starting to notice his lifestyle was having a detrimental impact on his body.
He wasn't as fit as he used to be and he often shunned the healthy food in his fridge for yet another take-away.
Stewart was often drinking more than 100 units of booze a week - the government recommends men should drink no more than 21 units.
And when Stewart got drunk, those around him felt he became a different person.
Stewart thought he was indestructible
His mother, April, said: "He is a demon. He becomes evil - and it all starts when he starts drinking."
Stewart's lifestyle was also starting to take its toll on his relationship with his live-in girlfriend Donella.
She had given him an ultimatum: "Stu needs to clean up his act. He needs to cut back on his drinking.
"If he doesn't do that, then I will have to seriously review the situation of our relationship, because he is going to lose everything if he doesn't stop."
With his relationship on a knife-edge, Stewart put himself forward for Make My Body Younger's "living autopsy".
Every inch of Stewart's body was examined and his vital organs were tested.
He even had a fertility test, though he felt confident about the outcome.
"I know I've got no problems," he said.
"I've got a daughter already. I know everything is working properly."
At his "living autopsy", Stewart was laid out and the first "incision" was made in front of girlfriend Donella, Stewart's mother and his brothers.
It was a demanding and emotional time for all involved as presenter George Lamb and Dr Andrew Curran revealed Stewart's results.
One of the most shocking moments for Stewart, Donella and his family was when his brain age was revealed, following a series of cognitive function tests.
Stewart is only 25 but all his hardcore partying resulted in a brain age of 68.
Donella's shock at him "having the brain of a pensioner" was something his entire family shared.
Fertility under threat
But for Stewart the greatest surprise was the state of his sperm.
Due to his excessive partying lifestyle, Stewart's fertility test showed his sperm had 91% deformed heads.
This left a serious question mark over his fertility as normal fertility allows for less than 70% deformed heads.
Stewart was left stunned by the news. "The sperm one was shocking, really bad," he said. "I was close to tears."
Back at home in Brighton, the surprises didn't end for Stewart.
He got his very own live-in medic in the shape of Dr Leanne Hayward.
She moved in with Donella and Stewart for three days and gave Stewart valuable information about how to live his life differently - but without having to become a party-free zone.
Stewart initially wanted to stop drinking and smoking altogether but this concerned Dr Hayward.
"We need to be really careful with Stewart that he doesn't totally stop everything because he could run into more problems," she said.
"He may be more likely to fall off the wagon if he tries to cut out absolutely everything."
Stewart and Donella found the early days a struggle and had a few rows.
But slowly Stewart started to feel the benefits of not drinking or smoking as much.
After several weeks, he went back to London for tests to find out the new biological ages of his key organs and the state of his sperm.
Because of Stewart's improved lifestyle his new brain age came in at 18 years, a massive drop and a testament to his hard work.
But probably the best news for Stewart and Donella was that his fertility test results showed the level of deformity of his sperm was back within the normal range.
Stewart was relieved by the results: "All the hard work has definitely paid off."
Donella too was delighted. "I've got my dream guy," she said. "Hopefully we will have a really long and happy future together."
Make My Body Younger is on BBC Three on Wednesday 16 July at 2000 BST and for seven days at .