An expansion of weight loss surgery in England is being proposed to tackle an epidemic of type 2 diabetes.
New draft guidelines from the National Institute of Health and Care Excellence (NICE) aim to reduce debilitating complications, which are a huge drain on NHS resources.
Diabetes UK estimates 850,000 people could be eligible for surgery, but NICE expects it to be tens of thousands.
Type 2 diabetes is closely linked to lifestyle and obesity.
The inability to control blood sugar levels can result in blindness, amputations and nerve damage.
A mounting body of evidence suggests a gastric bypass improves symptoms in around 60% of patients.
Current guidance says surgery is an option for people with a BMI above 35 who have other health conditions.
What is bariatric surgery?
Bariatric surgery, also known as weight loss surgery, is used as a last resort to treat people who are dangerously obese and carrying an excessive amount of body fat.
This type of surgery is only available on the NHS to treat people with potentially life-threatening obesity when other treatments have not worked.
Around 8,000 people a year are currently receiving the treatment.
The two most common types of weight loss surgery are:
Gastric band, where a band is used to reduce the size of the stomach so a smaller amount of food is required to make someone feel fullGastric bypass, where the digestive system is re-routed past most of the stomach so less food is digested to make someone feel fullNHS Choices Calculate your BMI
The update in guidance strengthens the focus on those with type 2 diabetes.
It explicitly states that people who have been diagnosed in the past decade and have a BMI over 35 should be assessed for surgery.
The guidelines also suggests doctors should consider those with a BMI of 30 or more on a case-by-case basis.
It means a man who is 6ft (1.83m) tall and weighs 18st 6lb (117kg) would be sent for an assessment, and doctors would be expected to consider sending a 5ft 5in (1.65m) woman, weighing 12st 10lb (80.7kg), as well.
Diabetes UK says around 460,000 people will meet the criteria for an automatic assessment under the guidance.
But the total jumps nearer to 850,000 when those with a BMI of 30 are also considered, it says.
The figures may be even higher as those of Asian descent should be considered at even lower, but unspecified, BMIs.
But NICE's Prof Mark Baker, who drafted the guidelines, said it was 'ridiculous' to think so many people would be operated on.
He told the BBC website: 'The first line of attack will be diet and exercise and we would expect clinicians to consider the risks and benefits of surgery for patients.'
He said some would not be operated on because of age, concluding: 'It would be between 5,000 and 20,000 operations a year, but we haven't done the modelling.'
Obesity statistics
One in four adults in England are obese A further 42% of men are classed as overweight The figure for women is 32% A BMI of 30-35 cuts life expectancy by up to four years A BMI of 40 or more cuts life expectancy by up to 10 years Obesity costs the NHS £5.1bn every year Source: National Institute of Health and Care Excellence BBC News: Where are you on the global fat scale?
Simon O'Neill from Diabetes UK said: 'Although studies have shown that bariatric surgery can help with weight loss and have a positive effect on blood glucose levels, it must be remembered that any surgery carries serious risks.
'Bariatric surgery should only be considered as a last resort if serious attempts to lose weight have been unsuccessful and if the person is obese.'
Around a tenth of NHS budgets is spent on diabetes.
Gastric bypass surgery can cost up to £15,000 and the move by NICE has raised concerns that the NHS will not be able to afford the treatment, even if there are savings in the longer term.
Tam Fry, from the National Obesity Forum, told the BBC: 'A considerable number of people who have had diabetes for some time and have been receiving medication will see a way out which has been sanctioned by NICE and they'll say that's for me.
'But the problem is the health service is going to say, 'No we're out of money, you can't have it', and that's going to create great friction.'
Low calorie diet
Meanwhile, the same guidance also says people should not be put on extreme diets to help them lose weight.
NICE acknowledges the diets have become increasingly popular, but warns they do not keep weight off in the long-term.
A very low-calorie diet consists of fewer than 800 calories a day. The normal level advised for an average man is 2,500 calories and for a woman it is 2,000.
Prof Mark Baker said: 'The new draft guidance now recommends that they [low calorie diets] should not be used routinely for people who are obese.'
The diets can still be used in the short-term, for a maximum of 12 weeks, for rapid weight loss before hip or knee replacement surgery or to meet criteria for fertility treatment.
The guidance states that 'regaining weight is likely' but that is not down to either 'their own or their clinician's failure'.
