Hopkinson J M, Butte N F, Ellis K J, Wong W W, Puyau M R, Smith E O
US Department of Agriculture, Agricultural Research Service, Baylor College of Medicine, Houston, TX, USA.
Am J Clin Nutr. 1997 Feb;65(2):432-8. doi: 10.1093/ajcn/65.2.432.
Accurate methods for determining body fat mass during reproduction are necessary to evaluate energy balance. However, determination of fat mass is complicated during pregnancy by the accretion of water, which invalidates assumptions underlying standard two-compartment models. The extent to which the variability in body water during pregnancy invalidates use of pregnancy-corrected two-compartment models for determination of fat mass in individual women is unknown. Moreover, it is unclear whether body water returns to nonpregnant values by 2 wk postpartum, which is frequently used as the baseline in studies of postpartum women. The present study uses a four-component model as a criterion for evaluating two- and three-component models. Fifty-six healthy, normotensive women between the ages of 19 and 35 y were studied at 36 +/- 1 wk gestation and 15 +/- 2 d postpartum. Total body water (TBW), total body potassium (TBK), body density, and bone mineral content were measured by deuterium dilution, whole-body potassium counting, hydrodensitometry, and dual-energy X-ray absorptiometry (postpartum only), respectively. At 2 wk postpartum, hydration and density of fat-free mass (FFM) had not returned to nonpregnant values, and differed between lactating and nonlactating women (P < 0.05). Accordingly, standard TBW and body density estimates of fat mass differed from four-component estimates at both time points (P < 0.005). Moreover, our data indicate that even when pregnancy-specific values for hydration or density of FFM are used in TBW and body density models, individual fat mass estimates may differ by > 3 kg from the four-component value. Fat mass by TBK may differ by > 10 kg from fat mass by the four-component model during pregnancy, and by 6 kg postpartum. Use of standard two-compartment models to estimate fat mass results in significant error both during pregnancy and at 2 wk postpartum. Pregnancy-corrected two-compartment models produce reliable mean fat mass estimates during pregnancy, but individual fat mass estimates may vary widely from four-component values.
在生殖过程中，准确测定体脂量对于评估能量平衡十分必要。然而，孕期由于水分的蓄积，脂肪量的测定变得复杂，这使得标准双室模型的基本假设无效。孕期体内水分的变异性在多大程度上使使用孕期校正双室模型来测定个体女性的脂肪量变得无效尚不清楚。此外，尚不清楚产后2周时体内水分是否恢复到非孕期水平，而这一时期常被用作产后女性研究的基线。本研究使用四成分模型作为评估双成分和三成分模型的标准。对56名年龄在19至35岁之间的健康、血压正常的女性在妊娠36±1周和产后15±2天进行了研究。分别通过氘稀释法、全身钾计数、水下密度测定法和双能X线吸收法（仅产后）测量了总体水（TBW）、总体钾（TBK）、身体密度和骨矿物质含量。产后2周时，无脂肪组织（FFM）的水合作用和密度尚未恢复到非孕期水平，且哺乳期和非哺乳期女性之间存在差异（P<0.05）。因此，在两个时间点，标准的TBW和身体密度法估算的脂肪量均与四成分法估算的结果不同（P<0.005）。此外，我们的数据表明，即使在TBW和身体密度模型中使用FFM水合作用或密度的孕期特定值，个体脂肪量估算值与四成分值之间的差异可能仍会超过3kg。孕期通过TBK估算的脂肪量与四成分模型估算的脂肪量之间的差异可能超过10kg，产后则相差6kg。使用标准双室模型估算脂肪量在孕期和产后2周都会导致显著误差。孕期校正双室模型在孕期可产生可靠的平均脂肪量估算值，但个体脂肪量估算值可能与四成分值有很大差异。
