Can being overweight really kill you? This spring, scientists at the Centers for Disease Control and Prevention lowered the national estimate for obesity-related deaths from 400,000 annually to no more than 26,000. But whatever the exact relationship between obesity and mortality, there is no question that excess weight can ruin your health. Obesity can foster diseases ranging from cancer to heart failure, and it's a clear factor in the country's growing epidemic of type 2 diabetes. That condition now affects more than 18 million Americans, including 5 million who remain undiagnosed. If current trends continue, a third of children born after 2000 will develop diabetes at some point in their lives. The disease can lead to kidney failure, blindness and blood-vessel damage requiring an amputation. So don't place too much stock in the latest mortality figures. If you value your legs and your eyesight, warding off type 2 diabetes should still be a priority.

Diabetes results from a gradual breakdown in the mechanisms that handle sugar in the body. Sugar is absorbed in the gut from food, stored temporarily in the liver and then released into the bloodstream as glucose. In response to the hormone insulin, which is produced in the pancreas, muscle and other cells take up glucose from the blood to use as fuel. When that process goes awry, glucose accumulates to toxic levels in the blood. For reasons that biochemists are only beginning to understand, excess body fat is strongly linked to developing diabetes--especially if it accumulates around the gut rather than the hips and thighs. With or without diabetes, the combination of a big waist, high blood pressure and impaired glucose tolerance (meaning that glucose levels don't drop as quickly as they should after eating) is known as metabolic syndrome. Experts now agree that this condition, which indicates an elevated risk for both cardiovascular disease and full-blown diabetes, needs to be brought under control, with drugs if necessary.

Insulin itself has been used to treat diabetes for decades, but today there are several options. One is metformin (approved and marketed as Glucophage), which works in several ways to lower blood sugar, primarily by reducing the secretion of glucose by the liver and by enhancing the action of insulin. Metformin can reduce the chances of progressing to diabetes by 31 percent in people with metabolic syndrome. Other promising treatments include the drugs known as thiazolidenediones--which are currently used to treat diabetes but may prove to be effective in preventing it--and a drug called rimonabant, which jams the brain's cannabinoid receptors. Marijuana boosts appetite by stimulating those receptors. Rimonabant seems to suppress appetite by blocking them. In a study published in The Lancet this spring, researchers found that nearly 40 percent of patients on rimonabant (versus 12 percent of those on placebo) lost 10 percent or more of their body weight over the course of a year. Blood cholesterol, insulin response and other indicators of metabolic syndrome were improved. If further studies confirm those findings, rimonabant could represent a significant advance in promoting weight loss and fighting diabetes.

Even better treatments could follow, as researchers learn more about the biological mechanisms of appetite and metabolism. But for now, lifestyle remains our most powerful weapon against type 2 diabetes. Between 1996 and 2002, the National Institutes of Health sponsored a study known as the Diabetes Prevention Program. The DPP included a lifestyle program designed to help people lose 7 percent of their initial body weight through calorie restriction and small doses (150 minutes a week) of moderate exercise, such as walking.

Participants in the 16-session program learned to set specific goals for nutrition, exercise and weight loss, and to anticipate situations that would challenge their willpower. Most of the 1,000 participants successfully embraced the program--and their risk of developing diabetes dropped by 58 percent. The decline was even greater--71 percent--among people older than 60. The practical lesson is clear. Diabetes is the quintessential lifestyle disease. But lifestyle diseases have lifestyle cures, and the only side effects are good ones.