Steve Way, who went from 16 and a half stone smoker to marathon runner, told ITV News competing at the Commonwealth Games was "quite a surreal" experience.
Way was 33 years old when he decided it was time to change his diet of beer, junk food and cigarettes for something more healthy.
He said, "It was just that point where you think, 'If I don't do something now then I might go down a route that I can't get back from.'
"It was, 'Let's lose some weight, let's find something to do while not smoking', and running was the answer for me."
Seven years later he finished the Commonwealth Games men's marathon as the fastest Englishman in the race.
"At the start of the marathon I was actually leading in the Commonwealth Games marathon, which did put a smile on my face," he said beaming.
He crossed the finishing line at Glasgow Green in a time of 2hrs 15mins 16secs.
"Just get out there," Way said when asked what he would say to people who want to follow in his footsteps.
"There might be a Commonwealth athlete hidden just beneath that couch potato suit so, you won't know until you give it a try, so keep on running."