Diabetes could be caused by a chemical in sugar - turning the condition on its head, according to new research.
If true, scientists say high blood glucose levels would be an affect - rather than the cause - of the disease.
Experiments on flies found found large amounts of the metabolite MG (methylglyoxal) led to the typical diabetic disturbances of the metabolism.
This led to insulin resistance, obesity and elevated blood sugar levels.
Dr Aurelio Teleman, of the German Cancer Research Centre in Heidelberg, said: 'It appears to be sufficient to increase the MG level to trigger insulin resistance and typical diabetic metabolic disturbances.
The findings, published in the journal Cell Metabolism, also raises the question about what might cause an elevated MG level.
For example, obese people who are not diabetic also display elevated MG levels.
Diabetes. affects more than four million Britons. The discovery could lead to the development of drugs that target MG.
Insulin resistance and elevated blood glucose levels are considered to be the cause of type 2 diabetes - the form caused by obesity.
It usually develops in middle or older age - causing severe health complications. It can lead to heart disease and strokes, massive blood flow problems in the legs as well as severe damage to eyes, nerves and kidneys.
These dangerous late effects are believed to be caused by high blood sugar levels which develop when the body cells no longer respond to insulin.
But Dr Teleman and colleagues say things might be completely different.
Blood glucose levels correlate with the level of diabetic symptoms. When very high blood glucose levels are lowered using drugs, the rate of infarctions and strokes as well as blood flow problems decrease in parallel.
Dr Nawroth, of Heidelberg University Hospital, said: 'But this holds true only up to a certain point.
'Large clinical trials in recent years have shown even when blood sugar could be lowered by drugs below the diabetes threshold value, many patients nevertheless developed typical diabetic damage to nerves and kidneys.
The researchers knew in type 2 diabetics high levels of MG have been observed - thought to have been an effect of elevated blood glucose.
Since MG can cause damage to proteins, textbook knowledge consequently holds that it must be one of the culprits in causing typical diabetic damage.
But in light of their recent results the metabolism experts have now doubted this sequence of events.
When rats are given MG with their food, they develop many typical signs of diabetes, including insulin resistance.
The researchers planned to investigate the effects of long-term elevated MG concentrations on the organism.
Using genetic engineering, the researchers turned off the enzyme that breaks down MG in flies.
The glucose metabolite MG subsequently accumulated in their bodies. The flies soon developed insulin resistance.
Later, they became obese and at higher age their glucose levels also became disrupted.
Dr Teleman said: 'Production as well as decomposition of MG is influenced by numerous metabolic processes which we do not know yet and have to understand better.