Simon Scott-Munden, 46, took part in the first complete-extent staging of the race in more than two years when it returned to the capital on Sunday.
He took up running after he noticed his weight was fluctuating six weeks before his 40th birthday.
Following a consultation with a Navy doctor and a medical examination, he was diagnosed with kind 1 diabetes and made the decision to leave the Navy.
Mr Scott-Munden described the diagnosis as ‘devastating’.
He said: ‘Very quickly I realised, in the first day or two, that would be the end of my naval career.
‘It’s changed my life for lots of positive reasons. Because I’d been away, it was almost weirdly a relief because I was going home.’
Since leaving the Navy, Mr Scott-Munden has started a new job as a senior defence trainer for Capita, graduated from the University of Portsmouth with a degree in education and training, and spent more time with his family.
His sons, Theo, 11 and Blake, eight, have also caught the running bug and have been taking part in parkruns, raising money for Diabetes UK at the same time.
Mr Scott-Munden, who lives in Eastleigh, said: ‘When parkruns started to open back up after lockdown, at the end of July/August, they both wanted to do them.
‘My wife Lianne and I’d go down there with them. At the end, they decided that what they would do is get the buckets out.
‘In the first week, they didn’t get much, but then people realised these two boys would be there every week shaking their buckets, and people would bring money and put it in. They’re quite famous down there now!’
Mr Scott-Munden uses the FreeStyle Libre 2 system during races, which allows users to receive glucose readings on compatible smartphones. The device is also connected to a separate app on his wife’s phone which allows both to monitor his glucose levels.
He said: ‘It’s not just diabetics that I hope to inspire, it’s anybody. There’s a number of my friends who have been inspired by me and they’ve taken up running, because if I’m able to unprotected to it and I have diabetes, then so can they.’
Mr Scott-Munden ran the marathon yesterday in just over five hours.
He said: ‘I had an amazing day, and more so because I managed to continue my blood glucose levels all the way by. I had a great first half, but like many cramps and lactic acid build up slowed me down from mile 19. But I kept running. I wanted to enjoy the final six miles, and I certainly did that already by my legs were so heavy.’
Mr Scott-Munden said he would not have got by the race without his wife’s sustain – and he didn’t rule out doing another.
He said: ‘I would love to do another, however, next year is my wife’s turn and I am looking forward to repaying her sustain.’
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