Nearly half of patients have reversed type 2 diabetes in a "watershed" trial, say doctors in Newcastle and Glasgow.
People spent up to five months on a low-calorie diet of soups and shakes to trigger massive weight loss.
Isobel Murray, 65, who had weighed 15 stone, lost over four stone (25kg) and no longer needs diabetes pills. She says: "I've got my life back."
The charity Diabetes UK says the trial is a landmark and has the potential to help millions of patients.
Isobel, from Largs in North Ayrshire, was one of 298 people on the trial.
Her blood sugar levels were too high, and every time she went to the doctors they increased her medication.
So, she went on to the all-liquid diet for 17 weeks - giving up cooking and shopping. She even ate apart from her husband, Jim.
Instead, she had four liquid meals a day.
It is hardly Masterchef - a sachet of powder is stirred in water to make a soup or shake. They contain about 200 calories, but also the right balance of nutrients.
Isobel told the BBC it was relatively easy as "you don't have to think about what you eat".
Once the weight has been lost, dieticians then help patients introduce healthy, solid meals.
"Eating normal food is the hardest bit," says Isobel.
The trial results, simultaneously published in the Lancet medical journal and presented at the International Diabetes Federation, showed:
46% of patients who started the trial were in remission a year later
86% who lost 15kg (2st 5lb) or more put their type 2 diabetes into remission
Only 4% went into remission with the best treatments currently used
Prof Roy Taylor, from Newcastle University, told the BBC: "It's a real watershed moment.
"Before we started this line of work, doctors and specialists regarded type 2 as irreversible.
"But if we grasp the nettle and get people out of their dangerous state, they can get remission of diabetes."
However, doctors are not calling this a cure. If the weight goes back on, then the diabetes will return.
"I will never go there again," says Isobel. So far, she has kept the weight off for two years.
Why does losing weight work?
Body fat building up around the pancreas causes stress to the beta cells in the organ that controls blood sugar levels.
They stop producing enough of the hormone insulin, and that causes blood sugar levels to rise out of control.
Dieting loses the fat, and then the pancreas works properly again.
The trial looked at only patients diagnosed in the past six years. It is thought having type 2 diabetes for very long periods of time may cause irreversible damage.
Prof Mike Lean, from Glasgow University, told the BBC: "It's hugely exciting."
"We now have clear evidence that weight loss of 10-15kg is enough to turn this disease around.
One in 11 adults worldwide has diabetes, and most of them have type 2.
Uncontrolled sugar levels cause damage throughout the body, leading to organ failure, blindness and limb amputations.
Treating the disease costs the UK's NHS about £10bn a year.
Dr Elizabeth Robertson, the director of research at Diabetes UK, said: "[The trial has] the potential to transform the lives of millions of people.
"The trial is ongoing, so that we can understand the long-term effects of an approach like this."
Isobel said: "I don't look at myself as a diabetic at all.
"You have to be fired up, you have to be prepared, but anybody can do it if you feel strongly enough."