People who have had obesity-related type 2 diabetes for years have been cured, at least temporarily, by keeping to an extreme, low-calorie, diet for two months, scientists report today.

The discovery, reported by scientists at Newcastle University, overturns previous assumptions about type 2 diabetes, which was thought to be a lifelong illness.

In the UK about two and a half million people have been diagnosed with diabetes, the large majority with type 2, and numbers are rising across much of the world. The condition has to be controlled with drugs and eventually insulin injections. It can cause blindness and end in foot amputation, as well as shortening life.

The results of the Newcastle investigation, though the study was small, demonstrated that full recovery was possible, not through drugs but through diet.

Eleven people with diabetes took part in the study, which was funded by Diabetes UK. They had to slash their food intake to just 600 calories a day for two months. But three months later seven of the 11 were free of diabetes.

"To have people free of diabetes after years with the condition is remarkable – and all because of an eight-week diet," said Roy Taylor, professor at Newcastle University, who led the study. "This is a radical change in understanding type 2 diabetes. It will change how we can explain it to people newly diagnosed with the condition. While it has long been believed that someone with type 2 diabetes will always have the disease, and that it will steadily get worse, we have shown that we can reverse the condition."

Type 2 diabetes, which used to be known as adult onset, is caused by too much glucose in the blood. It is strongly linked to obesity, unlike type 1, which usually develops in children whose bodies are unable to make the hormone insulin to convert glucose from food into energy. They need daily insulin injections.

The research, presented today at the American Diabetes Association conference, shows that an extremely low-calorie diet, consisting of diet drinks and non-starchy vegetables, prompts the body to remove the fat clogging the pancreas and preventing it from making insulin.

The volunteers were closely supervised by a medical team and matched with the same number of volunteers with diabetes who did not get the special diet. After just one week into the study, the pre-breakfast blood sugar levels of the study group had returned to normal. And MRI scans showed that the fat levels in the pancreas had returned to normal. The pancreas regained its ability to make insulin.

After the eight-week diet the volunteers returned to normal eating but had advice on healthy foods and portion size. Ten of the group were retested and seven had stayed free of diabetes.