Every inch of Stewart's body was examined and his vital organs were tested.
The sperm one was shocking, really bad - I was close to tears
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."