Mike Hare ditched his daily diet of calorie filled junk food and took up running.
He set up a blog site called 'The Incredible Shrinking Man' to chart his progress which became an instant hit.
''It's great because I've been able to pass on help and advice to others too. I hope I've managed to inspire and support people,'' Telegraph quoted him, as saying.
Hare, a market research firm owner from Peterborough, Cambs, decided to lose weight after becoming trapped in his car in a road accident.
By cutting junk food out of his diet and taking up running, he managed to drop from 28 stone to 13 stone, and now runs marathons in his spare time.
The blog helped him stick to his target weight, and was overwhelmed by the goodwill of fellow bloggers.
He has now met several of his fellow online dieters to swap tips and offer support.
''Every time I have raced, bloggers have turned up to either race with me or cheer me on,'' Hare said.
The businessmen, who completed this year's London Marathon in 5 hours 46 minutes, has now started his own website to inspire other people to turn their lives around.