Following experts' consensus, waist circumference (WC) is the best anthropometric obesity index. However, different anatomic sites are used, and currently there is no universally accepted protocol for measurement of WC. In this study, we compare the associations between WC measured at different sites with total visceral adipose tissue (VAT) volume and cardiometabolic risk. Cross-sectional data were obtained from 294 adults and 234 children and adolescents. In addition, longitudinal data were provided in 75 overweight adults before and after dietary-induced weight loss. WC was measured below the lowest rib (WC(rib)), above the iliac crest (WC(iliac crest)), and midway between both sites (WC(middle)). Volumes of VAT and abdominal subcutaneous adipose tissue (SAT) were obtained using MRI. Cardiometabolic risk included blood pressure, plasma lipids, glucose, and homeostasis model (HOMA index). WC differed according to measurement site as WC(rib) < WC(middle) < WC(iliac crest) (P < 0.001) in children and women, and WC(rib) < WC(middle), WC(iliac crest) (P < 0.001) in men. Elevated WC differed by 10-20% in females and 6-10% in males, dependent on measurement site. In men and children, all WC had similar relations with VAT, SAT, and cardiometabolic risk factors. In women, WC(rib) correlated with weight loss-induced decreases in VAT (r = 0.35; P < 0.05). By contrast, WC(iliac crest) had the lowest associations with VAT and cardiometabolic risk factors in women. Each WC had a stronger correlation with SAT than with VAT, suggesting that WC is predominantly an index of abdominal subcutaneous fat. There is need for a unified measurement protocol.

Background: Weight loss leads to reduced resting energy expenditure (REE) independent of fat-free mass (FFM) and fat mass (FM) loss, but the effect of changes in FFM composition is unclear. Objective: We hypothesized that a decrease in REE adjusted for FFM with weight loss would be partly explained by a disproportionate loss in the high metabolic activity component of FFM. Design: Forty-five overweight and obese women [body mass index (in kg/m 2 ): 28.7-46.8] aged 22-46 y followed a low-calorie diet for 12.7 6 2.2 wk. Body composition was measured by magnetic resonance imaging, dual-energy X-ray absorptiometry, and a 4-compartment model. REE measured by indirect calorimetry (REEm) was compared with REE calculated from detailed body-composition analysis (REEc) by using specific organ metabolic rates (ie, organ REE/mass). Results: Weight loss was 9.5 6 3.4 kg (8.0 6 2.9 kg FM and 1.5 6 3.1 kg FFM). Decreases in REE (28%), free triiodothyronine concentrations (28%), muscle (23%), heart (25%), liver (24%), and kidney mass (26%) were observed (all P , 0.05). Relative loss in organ mass was significantly higher (P , 0.01) than was the change in low metabolically active FFM components (muscle, bone, and residual mass). After weight loss, REEm 2 REEc decreased from 0.24 6 0.58 to 0.01 6 0.44 MJ/d (P = 0.01) and correlated with the decrease in free triiodothyronine concentrations (r = 0.33, P , 0.05). Women with high adaptive thermogenesis (defined as REEm 2 REEc , 20.17 MJ/d) had less weight loss and conserved FFM, liver, and kidney mass. Conclusions: After weight loss, almost 50% of the decrease in REEm was explained by losses in FFM and FM. The variability in REEm explained by body composition increased to 60% by also considering the weight of individual organs.Am J Clin Nutr 2009;90:993-1001.

Objective: To compare body composition determined by bioelectrical impedance (BIA) consumer devices against criterion estimates determined by whole body magnetic resonance imaging (MRI) and dual energy X-ray absorptiometry (DXA) in healthy normal weight, overweight and obese adults. Methods: In 106 adults (54 females, 52 males, age 54.2 ± 16.1 years, BMI 25.8 ± 4.4 kg/m²) fat mass (FM), skeletal muscle mass (SM), total body bone-free lean mass (TBBLM), and level of visceral fat mass (VF) were estimated by 3 single-frequency bipedal (foot-to-foot) and one tretrapolar BIA device, and compared to body composition measured by MRI and DXA. Bland-Altman and simple linear regression analyses were used to determine agreement between methods. Results: %FMDXA, SMMRI or TBBLMDXA showed good relative and absolute agreement with two bipolar and one tetrapolar instrument (r² = 0.92–0.96; all p < 0.001; mean bias <1.5 %FM and <1 kg SM or TBBLM) and less relative and absolute agreement for another bipolar device (r² = 0.82 and 0.84, mean bias ∼3 %FM and ∼3 kg SM). The 95% limits of agreement (bias ± 2 SD) were narrowest for the tetrapolar device (–6.59 to 4.61 %FM and –4.62 to 4.74 kg SM) and widest for bipolar instruments (up to –14.54 to 8.58 %FM and –9.52 to 3.92 kg SM). Systematic biases for %FM were found for all bipedal devices, but not for the tetrapolar instrument. Conclusion: Because of the lower agreement between foot-to-foot BIA and DXA or MRI for the assessment of body composition in individuals, tetrapolar electrode arrangement should be preferred for individual or public use. Bipolar devices provide accurate results for field studies with group estimation.