A routine eye appointment led Darren Rix to discover he was at high risk of developing type 2 diabetes.
His optometrist found "a wiggly vein" in the back of the eye which led to a blood test and pre-diabetes diagnosis.
Mr Rix, from Pontardawe, Swansea, then joined a diabetes prevention programme, which is available in parts of Wales.
It comes as public health experts warn that the number of people in Wales developing diabetes could rise sharply over the next decade.
There are already 212,716 people with the condition, but that could rise by 22% by 2035 if current trends continue.
It was once perceived as something that only affected older people, but cases of diabetes in Wales have already risen by 40% in the past ten years.
Type 2 accounts for 90% of cases of diabetes in the UK, and is where the body does not produce enough insulin, or the body's cells do not react to insulin properly.
This can be prevented through healthy eating, regular exercise and a healthy body weight, and can also be reversed with weight loss.
"The nurse did say 'it's a lifestyle change you're going to have to make, and if you don't you'll be heading up the scale to full diabetes and taking tablets every day'," Mr Rix said.
'No permanent fix'
The warning was enough to prompt the 50-year-old shift worker to reassess his routine.
"We went through my eating habits, which was embarrassing," he said.
He cut down his sugar intake, but exercising more and re-establishing his love of swimming, which he had not done for around 35 years, has been the biggest change to his lifestyle.
"My skills of swimming are still there, it's just the physicality and stamina is not there - my brain thinks I'm still young but my body says differently so I have to step back a bit and go slowly at it," he said.
Despite that, he has persevered and can now swim a mile in his hour swimming sessions, which he does three times a week.
"I've been monitoring my weight and I did start off at 14 stone 8lb, today I'm down to 12 stone 8," Mr Rix added.
"I went for my annual blood test and that showed I am out of the pre-diabetic zone, I'm in the normal zone."
He has been advised, however, that he needs to continue living more healthily.
'Really concerning rise'
Public health consultant Dr Amrita Jesurasa said 20 years ago, type 2 diabetes would have been perceived as a condition that affected just older people.
"But that's the shift we are seeing - not only are there lots more people, but there are lots more people who are younger as well," she said.
"Clinicians report seeing people who are in their 30s and 40s with type 2 diabetes, and that's not an uncommon occurrence, and even younger.
"That is really concerning, especially as it's preventable and there's something we can do about it."
The Welsh government said it was funding the pilot All Wales Diabetes Prevention Programme and was considering the next steps in its long term strategy to prevent and reduce obesity.
Public Health Wales has put a price on the cost of diabetes, with a medicines bill last year alone of £105m, and related hospital spells costing on average £4,518 per patient.
That does not include stays involving amputations, which the condition can lead to.
In 2021-22, more than 560 people had such surgery in Wales.
"Diabetes accounts for around 10% of the NHS budget, so it's a really significant financial pressure on the NHS, as well as being really significant for the health and wellbeing of the people of Wales," Dr Jesurasa said.
A prevention programme in parts of Wales identifies those at higher risk, and refers them to a healthcare worker to help make lifestyle changes.
Since its launch in June last year, it has helped more than 3,000 people.
Dr Jesurasa said many patients on the prevention programme were unaware they were at risk.
Charity Diabetes Cymru said the NHS "is under a lot of strain", adding: "What we're seeing is that people living with diabetes aren't necessarily getting all the checks they need at the right time.
"And this means their potential for going on to develop some of the awful complications that can come with diabetes, such as amputations, sight loss, heart attack and stroke is more likely, because they aren't getting those routine checks that they need to identify complications in the early stages."
A Welsh government spokesperson said: "The Welsh Unified GMS Contract, which sets out what services GP practices must provide, includes that GP practices 'will manage chronic disease in accordance with national guidance and best practice.'"