Public Health England states categorically for first time that excess weight is biggest risk factor for type 2 diabetes. Some 90% of people with the disease are overweight.

But note that abdominal fat is a better indicator of your chances of getting it than BMI. Men who measure more than 102cm (40 inches) around the middle are five times more likely to be diagnosed with type 2 diabetes than men with a smaller waist, while women who measure more than 88cm (35 inches) are three times more likely to be diagnosed than others.

http://www.theguardian.com/society/2014/jul/31/belly-abdominal-fat-type-2-diabetes