The lean patients looked metabolically similar to those who were obese—with the exception of their weight—the researchers found, but they were twice as likely to die at any point than their heavier counterparts. Even after adjusting for other risk factors known to contribute to diabetes, such as high blood pressure, high cholesterol levels and smoking, the higher mortality rates remained.
Further, to account for the possibility that the normal weight patients could have been losing weight due to other underlying illnesses, the researchers excluded people who died within two years of their diabetes diagnosis. The doubling of early death risk persisted.
Overall, the death rate in overweight and obese people with diabetes was 1.5 percent per year, compared with 2.8 percent in thin patients.
So, what sets the disease apart in normal weight people? More studies are needed to figure that out, but the authors have a few guesses. Genetic predisposition to improper insulin production may be part of the problem, says Carnethon.
“We need to explore the genetic variations related to insulin secretion,” Carnethon said. “It’s possible that genetic factors could be promoting insulin resistance, and influencing something else related to mortality. We really don’t know.”
It’s also possible that body fat may still play a role. The studies measured the participants’ body mass index (BMI), a ratio of their height and weight, but it wasn’t able to take into account their body fat composition, or how much of their overall body weight was made up of fat versus muscle.