Deurenberg P, Leenen R, Van der Kooy K, Hautvast J G
Department of Human Nutrition, Agricultural University, Wageningen, The Netherlands.
Eur J Clin Nutr. 1989 Aug;43(8):569-75.
By means of theoretical calculations it is shown that the chemical composition of the fat-free mass is affected by the amount of fat in the body. With increasing fatness the relative amounts of minerals and protein in the fat-free mass will decrease and the relative amount of water will increase. These changes in the chemical composition of the fat-free mass are confirmed by data from the literature. Because minerals and protein are the most dense components in the fat-free mass, and water is the less dense component, the density of the fat-free mass will decrease with increasing body fatness. As a consequence, the normally used computation formula for the calculation of the body fat percentage from whole-body density (Siri's equation) will systematically overestimate the real body fat percentage by as much as 2-4 per cent in severely obese subjects. This overestimation is large enough to correct for in studies on energy metabolism and body composition.
通过理论计算表明，去脂体重的化学成分受体内脂肪量的影响。随着肥胖程度增加，去脂体重中矿物质和蛋白质的相对含量会降低，而水的相对含量会增加。去脂体重化学成分的这些变化得到了文献数据的证实。由于矿物质和蛋白质是去脂体重中密度最大的成分，而水是密度较小的成分，去脂体重的密度会随着身体肥胖程度的增加而降低。因此，通常用于根据全身密度计算体脂百分比的计算公式（西里方程）在严重肥胖受试者中会系统性地高估实际体脂百分比达2% - 4%。这种高估在能量代谢和身体成分研究中足以进行校正。
