John Gibson's leg had been ulcerated, swollen and inflamed for weeks. "It looked like a damson from my toes to my knee," the 61-year-old recalls. His specialist suggested it would have to be amputated. "He whipped out a camera and photographed it. I said, Is this going to be the last time you see it?' and he said, It might be.'"

But when he next visited, Gibson explains as he sits at home in Mauchline, Ayrshire, the specialist was astonished to see that the leg had healed. "He asked me, Where's the ulcer?'" The former army nurse explained that his diabetes was now being managed on a special low-carbohydrate diet, recommended by his GP. "The specialist told me, Oh, we don't believe in that.'"

Indeed, most NHS doctors and dieticians are far from convinced by the way Gibson manages his diabetes. But Gibson's GP, Dr Katharine Morrison, is one of a vocal minority who contend that the orthodox advice given to type one and type two diabetes patients is not only unhelpful but might be counterproductive.

She believes that eliminating or at the very least strictly controlling carbohydrates is the only way diabetes patients can properly control their blood glucose levels. Unless they do this, she says, they remain at risk of the serious complications that can go hand in hand with the illness, including potential loss of limbs, blindness and kidney failure.

Lifestyle change is the first line of treatment for diabetes, type two in particular, with weight loss the main goal. Yet for decades, the standard advice has been that diabetics should cut out sugars and fats and replace them with a diet that is high in carbohydrates. The overall philosophy has been that diabetics should not be deprived of the pleasure of a normal diet.

Morrison disagrees - and she argues that the experiences of her own patients demonstrate that, by following a more restricted diet, patients can avoid the relatively large fluctuations in blood glucose that many accept as near-normal.

So do the experiences of her own son. Steven Morrison, 15, was diagnosed as a type one diabetic four years ago and follows a regime of low-carbohydrate meals, blood glucose monitoring and insulin injections after every meal.

Whether the close personal involvement with diabetes makes Morrison's position more or less credible depends on your own viewpoint. She certainly has a vested interest in being right; she is also passionate about her cause. The low-carb alternative is "patently obvious", she says. "The simple fact is, I will potentially save many more people's eyesight and limbs and even lives by promoting this approach than I will by being a GP."

She will promote low-carb diets at the International Forum on Quality and Safety in Health Care later this month in Paris, and she has devised an online training tool in the techniques for diabetics. It is based on the work of Dr Richard K Bernstein, himself a diabetic, who devised a diet for sufferers with the goal of controlling blood glucose. Since the publication of his book Dr Bernstein's Diabetes Solution in 1997, he has gained an international following. Morrison says that, at a recent forum held by Diabetes UK in Edinburgh, 70% of patients present said they wanted to know more about the low-carb diet.

"If you are swayed more by real people than by statistics, let me introduce you to some," she adds, backing up her points with success stories. But science doesn't move ahead by individual accounts - surely solid research and statistics have to back up clinical case studies? Morrison insists her approach is supported by such evidence.

What if she is right? Are thousands of diabetic patients suffering unnecessarily because official advice is leading them to suffer more and earlier complications, and putting type two diabetics at greater risk of needing to use insulin?

Diabetes UK continues to recommend that diabetic people follow the same balanced diet recommended for the rest of the population. Low in fat, sugar and salt, with plenty of fruit and vegetables, meals can contain some starchy foods such as bread, potatoes, cereals, pasta and rice. Carbohydrates with a lower glycaemic index - those that break down slowly - are better as they don't affect blood glucose as much, a spokesman for Diabetes UK said.

Stephen Fyfe, spokesman for the charity in Scotland, says research on the effects of low-carb diets has been limited in scope and duration. "Until the long-term effects prove the effectiveness and safety of low- carbohydrate diets, Diabetes UK does not recommend them."

However, the ground may be shifting. Diabetes UK and the International Diabetes Federation have commissioned research on the long-term effects, and Fyfe adds: "We may alter our recommendations to patients based on those findings."

The body responsible for making recommendations to doctors, the Scottish Intercollegiate Guidelines Network (Sign), has since 2001 been advising that diabetics be told to replace sugars and fats with carbohydrates. However, the entire Sign policy on diabetes is currently under review, and a spokesman said this process would take in the latest thinking and research.

Three factors are still hindering wider take-up of the low-carb message, Morrison believes. The first is a reluctance by the medical profession to concede possible mistakes. Secondly, drug companies and food manufacturers have a vested interest in promoting the high-carb option, she argues. A whole industry depends on medicating diabetics and providing them with specialist foods, which Morrison believes low-carb diets will eliminate.

But the third is also a significant hurdle: the low-carb regime is onerous for patients. In a recent briefing that she sent to her own health board, Ayrshire and Arran, Morrison admits that even her own patients have mixed reactions.

These range from the resistant - she quotes one type one patient who said: "I would rather die than give up my porridge in the morning" - to the indignant. "Look at these blood sugars - they are normal! Why wasn't I told about this years ago?" she says one patient told her.

The Herald contacted several Scottish diabetes specialists, each of whom was reluctant to comment on the diet advice given to patients. Perhaps this is because the issue remains so controversial. Across the Atlantic, the debate continues to rage, too. The American Diabetes Association has tentatively moved towards recommending low carbs, but diabetes specialist Hope Warshaw says many study subjects are unable to stick with Bernstein-style diets. "Diabetes lasts the rest of your life. You need to find an eating plan that you can follow for that long as well."

Young people in particular may find it difficult to avoid carbohydrates in a culture where the norm is to eat prepared food and fast food. But Steven Morrison is unperturbed. "It may be easier for me as I've never known anything else. I think it's harder for people who have to change what they've been doing for years," he says.