Regional fat mass by DXA: High leg fat mass attenuates the relative risk of insulin resistance and dyslipidaemia in obese but not in overweight postmenopausal women

Objective. To investigate the influence of regional fat mass (FM) on insulin resistance and dyslipidaemia in obese postmenopausal women (BMI > 30 kg/m(2)) compared to overweight women (BMI < 30 kg/m(2)). Leg FM may attenuate the increased risk of cardiovascular disease and diabetes imposed by increased trunk FM in normal and overweight postmenopausal women. Material and methods. Cross-sectional and consecutively referred patients comprising 63 obese and 36 overweight postmenopausal women. Body composition and regional FM by dual Xray absorptiometry (DXA), fasting glucose, fasting insulin and C-peptide, insulin resistance by homeostasis model assessment (HOMA-IR), insulin sensitivity by quantitative insulin sensitivity check index (QUICKI) and metabolic clearance rate (MCRestOGTT), insulin secretion (HOMAsecr) and serum lipids were assessed. Results. In obese subjects, leg FM was favourably associated with HOMA-IR (p < 0.05), QUICKI (p < 0.05), fasting glucose (p < 0.05), fasting insulin (p < 0.05), HOMAsecr (p < 0.05) and total cholesterol/HDL ratio (p < 0.05). Trunk FM was unfavourably associated with MCRestOGTT (p < 0.01), QUICKI (p < 0.05) and fasting insulin (p < 0.05). Compared to leg FM, leg/trunk FM ratio was more strongly associated with fasting insulin (p < 0.001), fasting C-peptide (p < 0.001), HOMA-IR (p < 0.001), MCRestOGTT (p < 0.001), QUICKI (p < 0.001), HOMAsecr (p < 0.001), fasting glucose (p < 0.01) and triglycerides (p < 0.01). Stepwise multiple regression demonstrated that leg/trunk FM ratio was the most important variable with partial R-2=0.26 (p < 0.001) for HOMA and R-2=0.37 (p < 0.001) when QUICKI was used as the dependent variable. In overweight women, no associations between fat mass and parameters of insulin resistance or dyslipidaemia were found. Conclusions. A high leg/trunk FM ratio as measured by DXA may give relative protection against diabetes and cardiovascular disease in obese postmenopausal women, but not in overweight women.