For the first time, doctors have convincing evidence that overweight people can lower their risk of diabetes by slimming down and exercising.

People who are obese and sedentary are more likely to develop type 2 diabetes, also known as adult-onset diabetes. Past studies have raised the possibility that a better diet and exercise can delay or prevent the disease, and doctors have long offered such advice to patients, but the new research is the first carefully controlled study to show this really works.

``This is now the proof that it can be done,'' said Dr. Jaakko Tuomilehto of Finland's National Public Health Institute, who headed the research reported in Thursday's New England Journal of Medicine.

The researchers calculated that the risk of diabetes was reduced by 58 percent in patients who were counseled how to lose weight, change their diet and exercise, compared with those who received only general advice.

``This gives us a challenge now to identify people at risk and begin to really focus on those individuals to make sure they recognize the need for lifestyle changes,'' said Dr. Robert Sherwin, president of the American Diabetes Association and professor of medicine at Yale University.

Diabetes is the seventh leading cause of death in the United States and is a growing problem worldwide. At least 16 million Americans have diabetes, which prevents the body from regulating blood sugar.

The disease can lead to blindness, kidney damage, amputation and heart disease. Some of the risk factors include age, obesity, a family history of diabetes and a lack of exercise.

The Centers for Disease Control and Prevention estimates that 6.9 percent of the adult population in 1999 had been diagnosed with diabetes. That followed a 33 percent jump between 1990 and 1998, to 6.5 percent.

``We have an epidemic on our hands and the outlooks don't look promising,'' Sherwin said.

The Finnish study involved 522 men and women who were middle-aged and overweight and had high blood sugar but not diabetes.

Half of the group got help losing weight and improving their diet - decreasing fat and increasing fiber - and increasing their daily exercise to at least 30 minutes. They met periodically with a nutritionist, who went food shopping with some participants.

``They got very detailed, individual advice, not only about what was in their food but also how to prepare it,'' Tuomilehto said.

The comparison group received general advice and written information about diet and exercise but was not offered any specific programs.

The participants were followed for about three years. During the first year, the average weight loss was about 9 pounds in the group that got detailed advice, compared with less than 2 pounds in the comparison group.

Diabetes was diagnosed in 27 people in the group that received advice and 59 in the comparison group.

A similar study is under way in the United States. The results are expected next year.

``That study hopefully will confirm this finding in a larger number of patients and in a much more diverse group of people,'' Sherwin said. ``I think then the issue will be resolved totally.''

　　From New England Journal of Medicine