Losing weight through diet and exercise can cut your risk of getting diabetes for at least 10 years, if you're overweight. Long-term results show that lifestyle change may work better than medication to prevent diabetes in people at high risk.

What do we know already?

One of the most common reasons for developing diabetes as an adult is putting on too much weight. More and more people are being diagnosed with diabetes, partly as a result of the increasing numbers of people becoming overweight or obese. Diabetes puts you at risk of some serious health problems, such as heart attacks, leg ulcers, and poor eyesight.

So, doctors are keen to find the best way to stop people who are overweight and at risk of diabetes from developing the condition. There were a number of these studies in the 1990s and 2000s, and we're now starting to see long-term results from them.

One of these studies compared a diabetes drug (metformin), a placebo (dummy treatment), and a lifestyle treatment (education and encouragement to exercise, follow a healthy diet, and lose weight). By the end of the study, the people who'd had lifestyle treatment had done best. They had lost more weight, and were less likely to have got diabetes. Metformin also had an effect, but not as big as the effect of diet and exercise.

After 2 years, the study ended and everyone was told the results. People were asked if they wanted to be in a follow-up study, and everyone was given advice about exercise, diet, and weight loss. People who'd taken metformin were allowed to continue with it if they wished. Everyone was followed for another 8 years.

What does the new study say?

At the end of the 10 years, people who'd been in the original exercise and diet group were still less likely to have diabetes. But the gap had narrowed. During the 8 years after the end of the original study, the numbers of people getting diabetes each year stayed about the same in the diet and exercise group (4.8 per hundred people, each year). But the numbers of people getting diabetes in the metformin and the original placebo group fell.

It's not clear why this happened. It may be that the lifestyle advice given to everyone at the end of the 2-year study had a positive effect on the people who'd had metformin or placebo.

The people who'd originally done exercise and diet had regained some of the weight they lost in the original study, but not all of it. Older people – who were more likely to attend the lifestyle advice sessions – did better at keeping the weight off.

How reliable are the findings?

The original 2-year study was a big randomised controlled trial. This is the best type of study for comparing treatments. So, the results from the original study are very reliable. But it's harder to be sure about the results from the 8 years of follow-up. That's because people were taking other types of diabetes medicines, everyone was advised about diet and exercise, and there were lots of things that could have made a difference to the results.

Where does the study come from?

The study was done by researchers across the US. It was published in the Lancet medical journal. It was funded by the US National Institute of Diabetes and Digestive and Kidney Diseases.

What does this mean for me?

It seems clear that there's no substitute for keeping weight down, exercising, and eating a healthy diet to help you avoid diabetes. The drug metformin may help, but it may work better if you also follow a healthy lifestyle. The good news is that making an effort to reduce your weight through diet and exercise seems to have a long-term benefit, even after 10 years.

What should I do now?

If you're concerned about your risk of diabetes, you could ask your GP surgery if you can have a diabetes test. The doctor or diabetes nurse should be able to advise you about ways to reduce your risk.

From:

Diabetes Prevention Program Research Group. 10-year follow-up of diabetes incidence and weight loss in the Diabetes Prevention Program Outcomes Study. The Lancet. Published online 29 October 2009.

© BMJ Publishing Group Limited ("BMJ Group") 2009