Dr. Oz says there are four major risk factors for type 2 diabetes:

Belly fat: A big belly is the number one risk factor in America, and Dr. Oz has a simple test to see if you have too much: "If your waist size, measured at your belly button is more than half of your height, then you've got too much belly and you're at risk for diabetes."

Sedentary lifestyle: Physical activity is key to preventing or reversing diabetes. "When you exercise and do muscle-building work, the muscle actually becomes more sensitive to insulin," he says. "The insulin can work better. It can drive the sugar where it's supposed to go."

Family history: "If you've got relatives who have diabetes or if you had diabetes when you were pregnant, big warning signs."

Smoking: Cigarettes not only harm your lungs, "it kills your pancreas," Dr. Oz says.