Overweight people have an advantage over everyone else that’s stumping medical experts. Researchers aren’t sure why, but overweight patients with type 2 diabetes live longer than those who are underweight, normal weight, or obese. They’re calling it the “obesity paradox” and have some theories as to why a little extra weight helps diabetics survive longer.

The study, published in the Annals of Internal Medicine, analyzed over 10,500 type 2 diabetes patients for more than 10 years and found an unusual trend: The overweight and obese patients were at greater risk for cardiovascular events, such as a heart attack or stroke, but the overweight group had a better chance at survival. And not just compared to the obese patients, but those who were overweight had better odds than those who were underweight or of normal weight with type 2 diabetes.

When a person has type 2 diabetes, they have rising blood glucose levels, also known as sugar levels, according to the American Diabetes Association. Their bodies aren’t able to process insulin properly because their pancreas isn’t able to keep up with how much sugar they’re ingesting or because their body is unable to use the insulin properly. It’s the most common form of diabetes, affecting 90 to 95 percent out of the 26 million Americans who are diagnosed with type 1 and type 2 diabetes.

Overweight and obese people are at a heightened risk for developing type 2 diabetes, especially if they’re over 45 years old, have a family member with it, live a sedentary lifestyle, have high blood pressure, or are of several minority groups.

Ten years ago researchers observed overweight and obese patients with coronary heart disease had better surgery outcomes than normal weight patients. They published their findings and described it as the “obesity paradox,” which is an umbrella term for overweight and obese people more likely to survive renal failure, heart failure, diabetes, and coronary heart disease, than their normal weight counterparts. Generally, if you’re obese you have a 50 to 100 percent increased risk of premature rate compared to someone of normal weight, but when it comes to the obesity paradox, the opposite seems to be true.

Researchers suspect the obesity paradox for type 2 diabetes may be because obesity’s metabolic stress causes a different type of type 2 diabetes than the type non-obese people suffer. Another theory is patients with type 2 diabetes who have lower body mass indexes might smoke more cigarettes and drink more alcohol than overweight people. The researchers caution not to gain weight if you’re diabetic and of normal weight. They’re still trying to figure out why overweight people have a seeming advantage over every other weight group. Until then, they encourage diabetics to stay as healthy as they can.

Source: Annals of Internal Medicine. 2015.