Duke University Medical Center researchers have shown that long-term, intensive exercise can significantly improve the body's ability to control blood sugar levels, adding further evidence that exercise can forestall the development of diabetes or cardiovascular disease in at-risk patients.

"It now appears that there is also a long-term beneficial effect from regular exercise, most likely due to the fact that a significant amount of fat is lost," said exercise physiologist Cris Slentz, Ph.D., author of a study appearing Feb. 15 in the journal Clinical Exercise Physiology. "Long-term exercise leads to loss of fat in the gut (stomach) region, which is especially beneficial since this fat is thought to be directly linked to increased risk of diabetes and heart disease."

The Duke researchers wanted to see how exercise influenced the way the body metabolized carbohydrates like glucose in people who had not yet developed diabetes, but were at high risk. Previous studies were not only short-term, but were conducted with elite or well-trained athletes who are not representative of the general population. The current study is the first of its kind using a "real-life" population of participants, the researchers said.

For their study, the Duke researchers put five overweight and sedentary people on an intensive exercise regimen for nine months, followed by a one-month "de-training" period. They measured blood levels of glucose and insulin before the exercise training began, as well as one day, five days and 30 days after the training ended. To keep these results from being influenced by what the patients consumed, the blood samples were taken after eight-hour fasts.

Insulin, a hormone that is secreted by the pancreas after eating, is responsible for the regulation of glucose levels in the blood; excessive amounts of insulin can, over time, lead to the complications associated with diabetes and heart disease.

"Insulin sensitivity, or its ability to stimulate glucose metabolism, was higher after nine months of exercise, and the fasting insulin levels were lower," Slentz said. "Just as importantly, 30 days after stopping exercise, insulin sensitivity was still 24 percent higher than pre-exercise levels, indicating that beneficial effects of exercise persisted."

"These results provide strong evidence that long-term exercise training can lead to both short-and long-term improvements in carbohydrate metabolism," said cardiologist Dr. William Kraus, senior member of the research team. "This demonstrates the clinical significance of regular exercise in preventing the development of insulin resistance and glucose intolerance in patients at risk for diabetes and heart disease."

Patients in the study did lose minimal amounts of weight (fat tissue weighs less than muscle tissue), demonstrating that weight alone is not necessarily a good marker for the risk of diabetes or heart disease.