Can we use the Jackson and Pollock equations to predict body density/fat of obese individuals in the 21st century?

A M Nevill, G S Metsios, A S Jackson, J Wang, J Thornton, D Gallagher
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Abstract

OBJECTIVE: Jackson and Pollock's (JP) ground-breaking research reporting generalized body density equations to estimate body fat was carried out in the late 1970s. Since then we have experienced an 'obesity epidemic'. Our aim was to examine whether the original quadratic equations established by Jackson and co-workers are valid in the 21st century. METHODS: Reanalyzing the original JP data, an alternative, more biologically sound exponential power-function model for body density is proposed that declines monotonically, and hence predicts body fat to rise monotonically, with increasing skin-fold thicknesses. The model also remains positive irrespective of the subjects' sum-of-skinfold thicknesses or age. RESULTS: Compared to the original quadratic model proposed by JP, our alternative exponential power-function model is theoretically and empirically more accurate when predicting body fat of obese subjects (sums of skinfolds >120mm). A cross-validation study on 14 obese subjects confirmed these observations, when the JP quadratic equations under estimated body fat predicted using dual energy x-ray absorptiometry (DXA) by 2.1% whereas our exponential power-function model was found to underestimate body fat by less than 1.0%. Otherwise, the agreement between the DXA fat (%) and the two models were found to be almost identical, with both coefficients of variation being 10.2%. CONCLUSIONS: Caution should be exercised when predicting body fat using the JP quadratic equations for subjects with sums of skinfolds>120 mm. For these subjects, we recommend estimating body fat using the tables reported in the present manuscript, based on the more biologically sound and empirically valid exponential power-function model.

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我们可以用Jackson和Pollock方程来预测21世纪肥胖者的体密度/脂肪吗?
目的:Jackson和Pollock (JP)在20世纪70年代末进行了开创性的研究,报告了广义体密度方程来估计体脂。从那以后,我们经历了一场“肥胖流行病”。我们的目的是检验杰克逊及其同事建立的原始二次方程在21世纪是否有效。方法:重新分析原始JP数据,提出了另一种更符合生物学原理的身体密度指数幂函数模型,该模型单调下降,从而预测身体脂肪随着皮肤褶皱厚度的增加而单调上升。无论受试者的皮肤折叠厚度和年龄如何,该模型都是积极的。结果:与JP提出的原始二次模型相比,我们的指数幂函数模型在预测肥胖受试者(皮肤皱褶总数>120mm)体脂时在理论上和经验上都更加准确。一项针对14名肥胖受试者的交叉验证研究证实了这些观察结果,使用双能x射线吸收仪(DXA)预测的JP二次方程低估了体脂2.1%,而我们的指数幂函数模型低估了体脂不到1.0%。另外,DXA脂肪(%)与两个模型之间的一致性几乎相同,变异系数均为10.2%。结论:在使用JP二次方程预测皮肤皱褶总数>120 mm受试者的体脂时应谨慎。对于这些受试者,我们建议使用本文中报告的表来估计体脂,基于更具有生物学合理性和经验有效性的指数幂函数模型。
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