Diabetes mellitus can result either from problems in the beta cells that produce and release insulin, or from the way insulin works on the storage tissues. Each of these problems leads to different types of diabetes. It is important for a doctor to know what type of diabetes the patient has so that the patient receives the appropriate treatment.

The most common type of diabetes, type 2 or adult-onset diabetes, starts in adulthood, typically after the age of 30. About 75 percent of all diabetics have type 2 diabetes. A common disease, it occurs in at least 10 percent of the U.S. population. Some 20 percent of people over the age of 60 have it. Type 2 diabetes frequently runs in families, so there is an important inherited tendency to develop this disease.

People with type 2 diabetes have two major problems with the way their bodies handle nutrients. First, the liver, muscles and fat cells are resistant to the effects of insulin. Thus, the storage tissues do not respond well to insulin produced in response to a meal. Secondly, patients with type 2 diabetes tend, over time, to make less and less insulin. Both problems lead to the buildup of glucose and other nutrients in the blood, which eventually results in tissue damage. Fortunately, most patients with type 2 diabetes continue to produce some insulin for many years and can take advantage of many treatment options available to increase the release of insulin from the pancreas and to make the tissues more sensitive to the insulin signal. When these treatments are successful, the need for insulin injections can be avoided.

About 8 of 10 patients with diabetes are overweight. In these individuals, obesity is an important contributor to their disease since we know that the tissues of overweight individuals become resistant to the effects of insulin. This is why diet and weight management are so important in the treatment of type 2 diabetes. In some individuals, diabetes can literally disappear if they lose enough weight.

Patients with type 2 diabetes usually develop the disease slowly as their weight increases. In fact, they usually have had the disease for many years before being diagnosed. In a large study recently conducted in England, 25 percent of patients with type 2 diabetes had the disease for 5 years or more before seeing a doctor about their symptoms.