Terry Barber, from Rayleigh in Essex, believes he weighed 25 stone at his highest point.
He has now lost fourteen stone and is preparing for his first marathon.
At 41 years old, Terry says "I completed my first half marathon in October and I now have my eyes on the Brighton Marathon in April.".
He claims that he tried countless different diet fads on his journey to lose weight, but nothing worked.
"I just lacked the self-discipline - the moment I wasn't concenctrating on being on a diet I found I was eating something!".
It was his young daughter that made him realise that further action was needed.
Consultant Bariatric Surgeon Mr Kesava Reddy Mannur, who he met at Spire Wellesley Hospital in Southend, helped him decide on the gastric sleeve option.
Mr Mannur said: "Like so many people in Terry’s situation he had tried almost every diet available but without success. He was caught in a vicious circle – his weight was increasing while his ability to exercise was getting less and less."
"He was actually dangerously overweight and very keen to do something about it so I suggested that a gastric sleeve would be his best choice of treatment."
"The operation is a minimally invasive procedure with most patients staying in hospital for a couple of nights - in fact, Terry only spent one night in the hospital."
"It is a highly-skilled procedure where three quarters of the stomach – including the area which contains ghrelin, known as the ‘hunger hormone’ - is removed. By reducing the stomach capacity as well as the desire for food, we give the patient a great."
After the gastric band was fitted, Terry saw a complete change in his eating habits, keeping portions small and seeing food as a fuel rather than a hobby.
Joining the gym allowed Terry to build up his confidence, as he first concentrated on weight training but then decided to start running and completed a 5k.
"It was a slow and frustrating start but, after a while, I decided to just go for it and run 5k – the goal was to complete the route no matter how long it took me. From there I built up my distance and my speed until, last October I completed a half marathon in One hour and fifty eight minutes."
He now weighs 11 stone and cannot thank Mr Mannur enough for 'his help, his advice and his surgical skills'.