For type 2 diabetes, this includes being overweight or obese (having a body mass index - BMI - of 30 or greater).

In fact, obesity is believed to account for 80-85% of the risk of developing type 2 diabetes, while recent research suggests that obese people are up to 80 times more likely to develop type 2 diabetes than those with a BMI of less than 22.

How does obesity cause type 2 diabetes?
It is a well-known fact that if you are overweight or obese, you are at greater risk of developing type 2 diabetes, particularly if you have excess weight around your tummy (abdomen).  
Inflammatory response
Studies suggest that abdominal fat causes fat cells to release ‘pro-inflammatory’ chemicals, which can make the body less sensitive to the insulin it produces by disrupting the function of insulin responsive cells and their ability to respond to insulin.
This is known as insulin resistance - the hallmark of type 2 diabetes. 
Waist /Hip Ratio   
Male  :  Below   0.9     
Female  : Below  0.8
Having excess abdominal fat (i.e. a large waistline) is

known as central or abdominal obesity, a particularly high-risk form of obesity.
Insulin Resistance 
Insulin resistance occurs cells of the body don’t respond to insulin. Insulin resistance is the name given to when cells of the body don’t respond properly to the hormone insulin.
Insulin resistance is the driving factor that leads to type 2 diabetes, gestational diabetes and pre diabetes. Insulin resistance is closely associated with obesity
Preventing Type 2 Diabetes
You will not develop type 2 diabetes automatically if you have prediabetes. For some people with prediabetes, early treatment can actually return blood glucose levels to the normal range.
Research shows that you can lower your risk for type 2 diabetes by 58% by:
• Losing 7% of your body weight (or 15 pounds if you weigh 200 pounds)
• Exercising moderately (such as brisk walking) 30 minutes a day, five days a week
Don't worry if you can't get to your ideal body weight. Losing even 10 to 15 pounds can make a huge difference.