Blood sugar tests can identify people at high risk of diabetes
Two key treatments do not halt diabetes in people with early signs of the disease, a large study has found.
Researchers said the results showed the only way to ensure future health in people at high risk of diabetes was exercise and a healthy diet.
Trials in more than 9,000 people also found no reduction in future heart problems in people prescribed two drug treatments compared with dummy pills.
Diabetes UK said 7m people in the UK were at risk of developing diabetes.
Everyone taking part in the study, published in the New England Journal of Medicine, had been diagnosed with what doctors call "impaired glucose tolerance".
It effectively means that people have high blood sugar and their bodies are starting to not respond to insulin as well as they should.
Sometimes called pre-diabetes, it is thought that the condition is a stage in the development of full-blown type 2 diabetes, and can be associated with obesity.
It is thought that in the UK, around 17% of 35-65 year olds have impaired glucose tolerance.
In the trial, researchers in the US and UK looked at whether using a drug that lowers blood pressure or a drug which lowers blood sugar could be used to stop diabetes developing in these high-risk patients.
But the results, from patients in 40 countries, found no great difference in how many people went on to get diabetes when prescribed either drug compared with a dummy pill.
Neither did the drugs prevent future heart attacks and strokes, which are dangerous complications of the condition.
In the blood-sugar lowering drug part of the study around a third of people went on to develop diabetes within five years whether they were taking the real medicine or dummy medicine.
Professor Rury Holman, director of the Diabetes Trials Unit at the University of Oxford, said the treatments were proven to be effective once someone had diabetes but there was an "urgent need" for drugs to prevent the disease and its complications developing in the first place in those at high risk.
He said: "The most successful treatment for someone at high risk of diabetes is diet and exercise."
Co-author Professor John McMurray from the University of Glasgow agreed that the results reinforced the importance of lifestyle changes in preventing diabetes.
"Losing as little as 5% of body weight has been shown to make a dramatic difference in other studies."
Dr Victoria King, research manager at Diabetes UK, said: "Unfortunately there is unlikely to be a quick and easy route to prevent type 2 diabetes and a healthy balanced lifestyle with a good diet and physical activity levels are the best preventative methods."
But she added some drugs may be of benefit in these patients and the latest study would help doctors prescribe the most appropriate option.
Professor Alan Maryon-Davis, president, UK Faculty of Public Health, said: "A huge number of people are in this 'nearly diabetes' category without realising it.
"We need to rapidly expand the national healthcheck programme, with many more community dietitians and exercise advisors ready to offer help."