Losing less than a gram of fat from the pancreas reverses the effects of Type 2 diabetes, British researchers say.
Experts from Newcastle University have found the disease - which causes more than five million deaths worldwide per year - is caused by fat accumulating in the pancreas.
The long-term condition, which can have serious consequences, occurs when there is too much glucose in the blood.
Professor Roy Taylor, who led the small trial, is publishing his findings in Diabetes Care and simultaneously presenting the results at a global conference in Vancouver.
His study tested 18 people with Type 2 diabetes and nine who did not, for weight, fat in the pancreas and insulin response before they had gastric band surgery, and again in eight weeks.
The diabetics were found to have originally had increased levels of fat in the pancreas.
Both groups lost about 13 per cent of their initial body weight.
Critically, the pool of fat in the pancreas did not change in the non-diabetics but decreased to a normal level in those with Type 2 diabetes.
Researchers said this showed the excess fat in the diabetic pancreas is specific to Type 2 diabetes and is important in preventing insulin being made as normal.
When that excess fat is removed, insulin secretion increases to normal levels. In other words, they were diabetes-free.
"For people with Type 2 diabetes, losing weight allows them to drain excess fat out of the pancreas and allows function to return to normal," Professor Taylor said.
"So, if you ask how much weight you need to lose to make your diabetes go away, the answer is one gram. But that gram needs to be fat from the pancreas.
"At present, the only way we have to achieve this is by calorie restriction by any means - whether by diet or an operation."
