The link between obesity and Type 2 diabetes is well established in most people’s minds, but it is excess visceral fat (fat that surrounds the internal organs) and insulin resistance — not obesity in and of itself — that puts people at increased risk for Type 2, according to new research published in The Journal of the American Medical Association.
Noting that obese people have varying levels of risk for developing prediabetes and Type 2 diabetes — millions of overweight and obese people do not develop either of these conditions — researchers from the University of Texas Southwestern Medical Center evaluated 732 obese individuals to determine specifically what factors might increase diabetes risk in this population.
Participants all had a body-mass index of 30 or greater, were between ages 30 and 65, and did not have diabetes or cardiovascular disease when they were enrolled in the Dallas Heart Study from 2000 to 2002. Information about a variety of factors was collected, including their family history of diabetes, body surface area, waist circumference, visceral and subcutaneous (under the skin) abdominal fat levels, liver fat, fasting blood glucose, levels of various biomarkers of insulin resistance, and cholesterol levels.
At a follow-up of seven years, 84 of the 732 participants had developed Type 2 diabetes. Having increased markers of insulin resistance, elevated fructosamine (a measurement indicating average plasma glucose level over several weeks), elevated fasting glucose, a family history of diabetes, increased systolic (the top number) blood pressure, weight gain over the follow-up period, and excess levels of visceral fat were all associated with an increased risk of developing Type 2 diabetes; excess visceral fat was linked with a more than twofold increase in the risk. General measures of obesity, however, such as body-mass index, total body fat, or subcutaneous abdominal fat were not associated with an increased risk of developing Type 2.
Roughly 39% of the 512 participants who’d had normal fasting glucose levels at the start of the study developed prediabetes, which was associated with elevated levels of visceral fat, fructosamine, and insulin; older age; non-white race; family history of diabetes; and weight gain over follow-up. Again, developing the condition was not associated with obesity itself.
“Our study may have implications for understanding differences between metabolically healthy and [unhealthy] obesity,” the study authors note.
According to lead study author James de Lemos, MD, the only way to determine whether fat is visceral or subcutaneous is with an imaging study such as magnetic resonance imaging (MRI).
For more information, read the article “Obesity Itself Not Diabetes Risk” or see the study’s abstract in The Journal of the American Medical Association. And to learn more about visceral fat, read the three–part series “Blasted Belly Fat,” by diabetes dietitian Amy Campbell.