Deurenberg P, Weststrate J A, van der Kooy K
Department of Human Nutrition, Agricultural University, Wageningen, The Netherlands.
Eur J Clin Nutr. 1989 Aug;43(8):559-67.
Using data from the literature on changes in the mineral content, muscle mass and the amount of water in the body during aging, the age-related changes in the chemical composition of the fat-free mass have been calculated. In men the decrease in minerals (bone loss) during aging equals the decrease in protein and water (muscle) in the fat-free mass. As a consequence the chemical composition of the fat-free mass is hardly affected by aging in men. In women, however, the loss of minerals during aging is considerably higher than the decrease in protein and water in the fat-free mass. As a consequence the change in the chemical composition of the fat-free mass in females is remarkable, and therefore in females, the density (kg/l) of the fat-free mass decreases with age. Consequently the body fat percentage calculated from body density with Siri's equation overestimates the real body fat percentage by 2-3 per cent, depending on age. Based on the calculated chemical composition of the fat-free mass at several ages, and its calculated theoretical density, Siri's equation has been adapted. In females but not in men the adapted formulas give a more valid estimate of the body fat percentage calculated from body density compared to Siri's formula.
利用文献中关于衰老过程中矿物质含量、肌肉质量和体内水分含量变化的数据，计算了无脂肪体重化学成分的年龄相关变化。在男性中，衰老过程中矿物质的减少（骨质流失）与无脂肪体重中蛋白质和水分（肌肉）的减少相当。因此，男性无脂肪体重的化学成分几乎不受衰老影响。然而，在女性中，衰老过程中矿物质的流失远高于无脂肪体重中蛋白质和水分的减少。因此，女性无脂肪体重的化学成分变化显著，因此在女性中，无脂肪体重的密度（千克/升）随年龄增长而降低。因此，根据西里公式由身体密度计算出的体脂百分比会高估实际体脂百分比2 - 3个百分点，具体取决于年龄。基于计算出的不同年龄无脂肪体重的化学成分及其计算出的理论密度，对西里公式进行了调整。与西里公式相比，调整后的公式在女性而非男性中能更有效地根据身体密度估算体脂百分比。
