Location of fat determines diabetes risk in obesity

By Sally Robertson, B.Sc.Sep 24 2012

New tools are needed to discriminate risk for prediabetes and diabetes among obese individuals, suggest findings from a US study.

A study of obese individuals found that general measures of fatness such as body mass index (BMI) had no bearing on their risk for developing diabetes, whereas excess visceral fat and biomarkers of insulin resistance were strong predictors of diabetes risk.

"Body mass index really isn't the whole story," lead author Ian Neeland (University of Texas Southwestern Medical Center, Dallas) told medwireNews.

"If you look at two people who are obese, their risk for diabetes may be vastly different because underneath the surface, you don't know where the fat is stored."

Markers of general adiposity that are associated with diabetes in the general population such as BMI, total body fat, and abdominal subcutaneous fat, were not associated with prediabetes or diabetes in the cohort of 732 obese individuals (BMI) who were followed up for a median of 7 years as part of the Dallas Heart Study.

However, multivariate analysis revealed that increases of 1 standard deviation in baseline visceral fat mass (1.4 kg), fructosamine level (1.1 µmol/L), fasting blood glucose ([FBG] 1.1 µmol/L), and homeostatic model assessment of insulin resistance (1.8 units) were significantly associated with an increased risk for incident diabetes, at respective odds ratios of 2.4, 2.0, 1.9, and 1.7.

Among 512 individuals who were normoglycemic at baseline, prediabetes or diabetes developed in 39.1% and was significantly associated with measures of visceral fat mass, FBG, insulin, fructosamine, non-White race, family history of diabetes, and weight gain over follow up. However, again, no associations with measures of general adiposity were observed.

Importantly, the team observed that BMI, total body fat, and abdominal subcutaneous fat mass did not differ between those who developed prediabetes or diabetes and those who remained metabolically healthy.

Resistance to diabetes in these individuals may depend on the ability to shunt excess fat away from visceral and other ectopic sites and preferentially deposit it in the lower body subcutaneous tissue, writes the team in JAMA.

"It would be great if we could identify obese patients who are at highest risk for diabetes using the assessment of adipose tissue distribution, visceral fat, and then target our therapies to those patients specifically or more intensively," said Neeland.

"Or if therapies could be developed that could modify the distribution of fat storage and shunt it away from visceral fat to fat in the functional areas, like the subcutaneous tissue."

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