The father of three's weight had crept to more than 21-and-a-half stone and he used to "break into a sweat" bending over to tie his shoelaces.
Mr Spence, a clerical officer for East Coast rail, blames having a deskbound office job and overeating for his weight problem, but had never been able to stick at the gym.
The 43-year-old, from Gilmerton in Edinburgh, said: "I had tried to do fitness things before, and my motivation had let me down.
"But coming to Hibs and doing the Football Fans in Training Programme gave me a lot more confidence to continue with it.
"Since then, I've done an 18-lap run around the pitch at Easter Road for charity. I play 90 minutes of football and five-a-side.
"Things I wouldn't have looked at before now, I do now. I also learnt so much about things like portion sizes: you already know you might be eating too much, but seeing it in front of you makes all the difference. It's just been a fantastic experience."
Mr Spence, who now weighs around 18-and-a-half stone, said the programme had transformed his attitudes to food.
"My problem was portion control. I was eating far too much, but I didn't realise until we were in the classes and they would lay out platefuls of food.
"You'd have eight plates of chips in front of you, going from plate one with a few chips on it, up to plate eight which was the biggest helping and we were asked to say what we thought was normal.
"My answers were always at the high end.
"That's been the major thing for me, getting my portions under control. Now I cook for my family and I cook really healthy dishes. I would never even have thought about cooking before - it would have ended in disaster. It's changed my life."