Just because a person gains weight doesn't mean she's going to get type 2 diabetes. Having a body mass index over 25 is just one of several risk factors for diabetes, but there are many overweight people who don't ever get the disease, McLaughlin says. Still, being obese—having a body mass index of 30 or more—is considered to be a major risk factor, and the increase seen in diabetes diagnoses has coincided with a dramatic increase in obesity in the United States, according to the CDC.
Other risk factors for diabetes include being older than 45, a lack of regular physical activity, or a family history of diabetes. You're also at risk if you have high blood pressure, high cholesterol, polycystic ovary syndrome, metabolic syndrome, or acanthosis nigricans (a condition that causes dark, thickened skin around the armpits or the neck). Having suffered from gestational diabetes during pregnancy or given birth to a baby weighing more than 9 pounds also raises the risk of the disease. And African-Americans, Hispanic Americans, Asian-Americans, and American Indians are at higher risk than are Caucasians.