People with diabetes are unable to control the level of sugar in their blood, usually due to a breakdown in how their bodies use the hormone insulin. It’s not completely clear how obesity can contribute to diabetes, but it is known that excess weight is associated with chronic inflammation and a dysfunctional metabolism. And these factors in turn make it easier for someone to stop responding to the presence of insulin as easily as they once did. So by using surgery to help very obese people with diabetes lose weight, the logic goes, you can indirectly treat or prevent the condition. But doctors such as David Cummings, a senior investigator at the University of Washington’s Diabetes & Obesity Center of Excellence, are pushing back against this way of thinking.

Family or personal history. Your risk increases if you have prediabetes — a precursor to type 2 diabetes — or if a close family member, such as a parent or sibling, has type 2 diabetes. You're also at greater risk if you had gestational diabetes during a previous pregnancy, if you delivered a very large baby or if you had an unexplained stillbirth.

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