Losing less than one gram of fat from the pancreas reverses the effects of Type 2 diabetes, according to a new study.
Experts from Newcastle University have found the disease - which affects two-and-a-half million people in the UK and is on the increase - is caused by fat accumulating in the pancreas.
The long-term condition, which can have serious consequences for patients, 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 eight weeks after.
The diabetics were found to have originally had increased levels of fat in the pancreas.
Both groups lost about 13% 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.
Prof Taylor said: "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.
"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."
Prof Taylor added: "This new research demonstrates that the change in level of fat in the pancreas is related to the presence of Type 2 diabetes in a patient.
"The decrease in pancreas fat is not simply related to the weight loss itself. It is not something that might happen to anyone whether or not they had diabetes. It is specific to Type 2 diabetes.
"What is interesting is that regardless of your present body weight and how you lose weight, the critical factor in reversing your Type 2 diabetes is losing that one gram of fat from the pancreas."