Centro de Investigación en Alimentación y Desarrollo, A.C. Coordinación de Nutrición, Carretera Gustavo Enrique Astiazarán Rosas #46, Col. La Victoria, C.P. 83304, Hermosillo, Sonora, México.
Universidad Autónoma de Ciudad Juárez, Instituto de Ciencias Biomédicas, Departamento de Ciencias de la Salud. Ave. Plutarco Elías Calles #1210, Col. Fovissste Chamizal, C.P. 32310, Ciudad Juárez, Chihuahua, México.
Clin Nutr. 2021 May;40(5):3592-3600. doi: 10.1016/j.clnu.2020.12.020. Epub 2020 Dec 29.
BACKGROUND/OBJECTIVES: Densitometry (Siri's and Brožek's equations), hydrometry (by the deuterium dilution technique), and dual-energy X-ray absorptiometry (DXA) are three methods for estimating body composition. However, because they are all based on certain assumptions, they may not be applicable to aged and obese subjects due to changes in their body composition. Hence, the validity of these "laboratory methods" could be affected in obese older people. The main aim was to assess the agreement between densitometry, hydrometry, and DXA with the 4-compartment (4C) model to estimate fat mass (FM) in obese older Hispanic-American adults. As secondary goals, we explored whether the bias in densitometry and hydrometry results could be improved by modifying the assumptions regarding fat-free mass (FFM) density and hydration factor (HF) values, respectively. In the case of DXA, we explored the factors that contribute to bias.
SUBJECTS/METHODS: This is a cross-sectional study based on a sample of 171 obese subjects aged ≥60 years from 3 regions of northern Mexico. Body composition was assessed by the 4C model as the reference method and by all three laboratory methods. Agreement of the latter with the 4C model was probed by Bland and Altman analysis, a paired sample t-test, and simple linear regression analyses. In addition, the mean FFM density estimated in this sample, and HF values (published previously) of 0.737 and 0.753 for obese older Hispanic-American men and women, respectively, were considered as ethnic- and gender-specific values. These values were used to modify the densitometric and hydrometric equations in order to improve their bias. Finally, we tested whether the hydration status and indirect markers of adiposity are contributing factors to the bias of DXA using multiple linear regression analysis.
Siri's equation overestimated FM by 0.57 kg (p < 0.01), while Brožek's equation, hydrometry, and DXA underestimated it by 1.24 kg, 0.89 kg, and 0.79 kg (p < 0.01), respectively, compared to the 4C model. The bias in the densitometry and hydrometry results was eliminated by substituting the ethnic- and gender-specific values into the equations. Finally, we found that hip circumference contributes to the bias in DXA.
The densitometry, hydrometry, and DXA methods are not interchangeable with the 4C model for assessing fat mass in obese, older Hispanic-American adults. The lack of agreement could indicate that the assumptions of each method do not apply to this population.
背景/目的：体成分评估的三种方法分别是：密度测定法（Siri 方程和 Brožek 方程）、容量测定法（利用氘稀释技术）和双能 X 射线吸收法（DXA）。然而，由于这些方法都是基于一定的假设，因此对于肥胖和老年人，其体成分可能会发生变化，所以这些“实验室方法”可能不适用。因此，肥胖老年人的这些“实验室方法”的有效性可能会受到影响。本研究的主要目的是评估密度测定法、容量测定法和 DXA 与 4 compartment（4C）模型之间的一致性，以评估肥胖的老年西班牙裔美国人的脂肪量（FM）。作为次要目标，我们探讨了通过分别修改关于去脂体重（FFM）密度和水合因子（HF）值的假设，是否可以改善密度测定法和容量测定法结果的偏差。对于 DXA，我们探讨了导致偏差的因素。
受试者/方法：这是一项基于来自墨西哥北部 3 个地区的 171 名年龄≥60 岁肥胖受试者的横断面研究。以 4C 模型作为参考方法和所有三种实验室方法来评估体成分。通过 Bland 和 Altman 分析、配对样本 t 检验和简单线性回归分析来探讨后者与 4C 模型的一致性。此外，还考虑了在本研究样本中估计的平均 FFM 密度和 HF 值（先前已发表），分别为 0.737 和 0.753，分别适用于肥胖的老年西班牙裔美国男性和女性。这些值被用来修改密度测定法和容量测定法方程，以改善其偏差。最后，我们使用多元线性回归分析来测试水合状态和间接肥胖指标是否是 DXA 偏差的影响因素。
与 4C 模型相比，Siri 方程高估 FM 0.57kg（p<0.01），而 Brožek 方程、容量测定法和 DXA 分别低估 FM 1.24kg、0.89kg 和 0.79kg（p<0.01）。通过将种族和性别特异性值代入方程，可以消除密度测定法和容量测定法结果的偏差。最后，我们发现臀围会导致 DXA 的偏差。
在评估肥胖的老年西班牙裔美国人的脂肪量时，密度测定法、容量测定法和 DXA 方法与 4C 模型不能互换。缺乏一致性表明，每种方法的假设都不适用于该人群。
