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Author: Nutrition Research Newsletter
Obesity is a known determinant of insulin resistance (IR) and a strong risk factor for type 2 diabetes. Excess central adiposity appears to be strongly associated with IR and increased risk of diabetes. Because not all studies have found that visceral fat confers a greater degree of IR than subcutaneous fat, there is a debate whether visceral fat is related to IR independently of overall fatness, especially among obese subjects.
Despite the strong associate between obesity, IR and type 2 diabetes, the mechanisms in which increased body fat impairs insulin action in other tissues are not clear. Recent research suggests that biomarkers of inflammation [C-reactive protein (CRP), interleukin-6 (IL-6), or tumor necrosis factor-a (TNF-a)] or endothelial dysfunction [such as E-selectin or intercellular adhesion molecule-1 (ICAM-1)] are associated with IR and increased risk for type 2 diabetes.
In order to explore the role of inflammation and endothelial dysfunction in mediating the association of overall or central adiposity with IR and risk of type 2 diabetes, researchers classified a sample of nondiabetic women participating in the Nurses' Health Study according to overall or central adiposity, both, or neither and compared fasting insulin (FI) levels (as a surrogate measure of IR) across categories. They then controlled for levels of inflammatory and endothelial biomarkers to test the hypothesis that these account for any association of weight phenotype with IR. Additionally, the risk for incident type 2 diabetes in these women was analyzed using a nested case control design to test the hypothesis that central adiposity is an independent risk factor for type 2 diabetes and that this risk is mediated by insulin levels and levels of inflammatory and endothelial biomarkers.
A total of 519 initially nondiabetic women were divided into four phenotypes above/below median BMI (27 kg/[m.sup.2]) and waist circumference (81 cm): low BMI-low waist (LBLW; N= 190), low BMI-high waist (LBHW; N= 27), and high BMI-high waist (HBHW; N = 219).