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Both insulin resistance and abdominal fat patterning are related to aging, and have been related to cardiovascular disease (CVD) risk factors such as dyslipidemia and hypertension. However, previous studies have not used direct methods to quantify the independent strength of the association of each of these two putative primary factors with metabolic outcomes. We quantified overall obesity by the body mass index (BMI) and used a previously validated magnetic resonance imaging (MRI) method to quantify abdominal fat in 63 healthy nondiabetic individuals aged 22 to 83 years. We also measured the glucose and insulin response to an oral glucose tolerance test and the insulin sensitivity ([SI] by modified minimal model analysis). Body fat patterning was evaluated by the waist to hip ratio (WHR) and by MRI, which allowed direct measurement of subcutaneous (SCF) and intraabdominal (IAF) fat depots at the umbilicus in these subjects. These independent parameters were related to risk factors for CVD (blood pressure, lipids, and lipoproteins) and to plasma concentrations of free fatty acids (FFAs). Measures of overall obesity (BMI), total fat [TF], and/or SCF measured at the abdomen by MRI), glucose/insulin metabolism and SI, and central fat patterning (WHR or IAF measured by MRI) were correlated with mean arterial pressure (MAP), triglyceride (TG), and high-density lipoprotein cholesterol (HDL-C) levels in univariate analysis and after controlling for age and gender. An index of central fat patterning (WHR) added to the informativeness of the insulin area under the curve (IAUC) in explaining 24% of the variability in plasma TG concentration, but measures of overall obesity were not independently related. Both the BMI and TF contributed to the IAUC in explaining 32% to 34% of the variability in MAP, but central fat patterning was not independently related. No index of overall obesity, fat patterning, glucose/insulin metabolism, and/or SI, was independently related to the plasma concentration of HDL-C after controlling for any one of the other two. Direct measurement of glucose/insulin metabolism and SI, as well as fat patterning, provides information on their relative associations with CVD risk factors. The measures of glucose/insulin metabolism and SI were more consistently related to dyslipidemia and hypertension than were the overall obesity and fat patterning in this healthy population.
Accurate measurement of central fat patterning is difficult to obtain by conventional anthropometry. Direct measurement of intra-abdominal fat area by magnetic resonance imaging, while accurate, is impractical for large-scale observational studies. This report examines the sex-specific associations of conventional anthropometric indices with intra-abdominal fat and subcutaneous fat areas measured by magnetic resonance imaging. A total of 157 volunteers (97 men and 60 women) aged 48-68 years of predominately white ethnicity had intra-abdominal fat and subcutaneous fat areas measured as part of the Atherosclerosis Risk in Communities (ARIC) Study. Weight, body mass index, waist circumference, waist : hip ratio, and subscapular skinfold thickness were measured or calculated by a standardized protocol. On average, women had a lower intra-abdominal fat area than men (109.5 cm2 vs. 152.9 cm2) but a higher mean subcutaneous fat area (287.8 cm2 vs. 214.6 cm2). After adjustment for age, intra-abdominal fat area was quadratically associated with body mass index, waist circumference, weight, and subscapular skinfold thickness in men; in women, these associations were best modeled by a positive linear equation. Waist : hip ratio was linearly related to intra-abdominal fat area in both sexes. In general, anthropometric measures predicted lower percentages of the total variance in intra-abdominal fat area for men than for women. For subcutaneous fat area, all anthropometric indices were linearly associated and predicted more of the variance in subcutaneous fat area than in intra-abdominal fat area. These results indicate that among men, greater intra-abdominal fat deposition rates occur at relatively low body weights and fat is more uniformly deposited at higher weights. Women appear to deposit intra-abdominal fat at a constant rate as they gain weight, even after menopause. The authors conclude that when waist circumference or body mass index is used as a surrogate for intra-abdominal fat area in men, a quadratic term should be included in the analysis as a predictor variable. Subcutaneous fat area can be estimated well by linear measures commonly employed in epidemiologic studies.
We evaluated two magnetic resonance imaging (MRI) methods, spin echo and inversion recovery (IR), for quantification of intraabdominal fat in a subgroup of participants from the Atherosclerosis Risk in Communities (ARIC) Study. Both methods were used previously to quantify visceral fat, and the IR but not the spin echo method has been validated by comparison with computed tomography in human beings. In the present study, the reliability of both methods was excellent: reliability coefficients comparing two readers on the same scan were 0.9574 for IR (n = 158) and 0.9254 for spin echo (n = 47) when random effects models with log-transformed data were used. A comparison of visceral fat areas in 47 subjects with both IR and spin echo indicated that IR gave a slightly higher mean area than did spin echo: 134.9 compared with 129.8 cm2. However, a mixed-model analysis of variance (ANOVA) of the log-transformed data showed no statistical difference between either method or readers in the comparison of IR and spin echo. These data suggest that the IR and spin echo protocols evaluated in this communication are comparable with one another and reliable for estimation of intraabdominal fat.
In a case-control study involving 268 cases of endometrial cancer and an equal number of population controls, we assessed the relationship of risk to body weight and fat distribution, examining weight at various ages and current anthropometric measurements. Weight gain during later adulthood and resultant high body masses were important risk predictors, indicating that obesity is an important risk factor, even in an area where the prevalence of obesity and incidence of endometrial cancer are low. Certain fat distribution patterns were related to risk of endometrial cancer independent of general obesity. In particular, fat deposits on the trunk were associated with elevated risks, with the odds ratio for the highest versus lowest quartile of subscapular skinfolds remaining significant even after adjustment for body mass index (odds ratio = 2.9; 95% confidence interval, 1.1-7.3). Central versus peripheral obesity, as measured by the subscapular:triceps ratio, also was related to increased risk, although the association failed to remain significant after adjustment for body mass (highest to lowest quartile, odds ratio = 1.7). In contrast, upper body obesity, as assessed by the waist:thigh ratio, was unrelated to risk. These results support the need for future studies assessing the relationship of hormonal and other biological parameters of fat distribution to assist in identifying causal mechanisms for this tumor.