An estimated 20.8 million Americans -- or 7 percent of the population -- are now believed to be diabetic. Of those, 6.2 million people have the disease but don't know it. And that doesn't include the 41million people with pre-diabetes.

In fact, the epidemic has become so pervasive that doctors are now finding patients who suffer from both type 1 and type 2 diabetes -- a phenomenon known as "double diabetes" or "hybrid diabetes."

"It's mostly people who have type 1 diabetes who become overweight and show the profile of a type 2, with obesity and hypertension," said Dr. Stewart Weiss, an assistant clinical professor of medicine at New York University School of Medicine in New York City.

Doctors and health-care experts are urging people to take the steps necessary -- basically proper nutrition and plenty of exercise -- to avoid joining the ranks of those already diagnosed with the disease.

Type 1 diabetes is caused by the body's inability to produce insulin, the hormone that ushers blood sugar -- called glucose -- to cells for energy. An estimated 5 percent to 10 percent of Americans with diabetes have type 1 disease. Type 2 diabetes results from insulin resistance -- the body's inability to properly use the hormone. Most Americans diagnosed with diabetes have type 2 diabetes, and excess weight and lack of exercise are big contributors to this form of the disease.

But, doctors are now seeing strong indications that double diabetes is a growing phenomenon. For instance, recent studies suggest that as many as 30 percent of newly diagnosed diabetes cases among children involve youngsters with both type 1 and type 2 diabetes.

Generally, double-diabetes sufferers will often look as though they have the more common type 2 version because they're overweight. But subsequent blood tests reveal they also have type 1 disease.

Double diabetes takes the suffering caused by the disease a step further, and complicates efforts to treat it.

Type 1 diabetics normally have to take daily injections of insulin to remain healthy, while type 2 diabetics require different medication and regular monitoring of their blood sugar. Doctors now are researching how to juggle treating both types of diabetes in the same patient, Weiss said.

"We have all sorts of medications that address different problems for different types of diabetes," Weiss said. "The question with double diabetes becomes, when can we use the different types of medications and what would be appropriate for different patients?"

Weiss suspects that double diabetes might be caused, in part, by type 1 diabetics who are taking insulin but haven't made the other lifestyle changes necessary to deal with the disease.

"One of the consequences of proper insulin use is weight gain," he said. "Often, patients who have not had a good understanding of how to eat are taking the insulin to cover what they normally eat."

The federal Diabetes Prevention Program study found that diet and exercise actually worked better than some medications in delaying the development of diabetes, according to the association. Just 30 minutes a day of moderate physical activity, coupled with a five percent to 10 percent reduction in body weight, produced a 58 percent reduction in diabetes.

Weiss recommends improving diet by eating more vegetables, fewer starches and more lean meat and fish. "I like to say there's no medication that can overcome a bad diet," he said.

He also said people should not only eat healthier, but they should try to eat less, too.

"The problem really is overeating in general," he said. "The portion size put before us is very large, so portion control is the single most important thing. You've got to know when to say when."