a Chairman of Scientific Advisory Board, Mannatech, Inc. , Coppell , Texas.
b Biomedical Informatics, Integrative Health Technologies, Inc. , San Antonio , Texas.
J Am Coll Nutr. 2018 May-Jun;37(4):302-307. doi: 10.1080/07315724.2017.1397566. Epub 2018 Feb 9.
A general assumption is that the body mass index (BMI) reflects changes in fat mass (FM). However, it fails to distinguish the type of weight that is lost or gained-fat mass (FM) or fat-free mass (FFM). The BMI treats both changes the same although they have opposite health consequences. The objective of this study was to propose a more precise measure, a body composition change index (BCCI), which distinguishes between changes in FM and FFM, and this study compares it with using the BMI as an outcome measure.
Data were obtained from 3,870 subjects who had completed dual-energy x-ray absorptiometry (DEXA) total body scans at baseline and end-of-study when participating in a variety of weight-loss interventions. Since height remained constant in this adult cohort, changes in the BMI corresponded with scale weight changes (r = 0.994), allowing BMI changes to be converted to "lbs." to match the statistic used for calculation of the BCCI. The BCCI is calculated by scoring increases in FFM (lbs.) and decreases in FM (lbs.) as positive outcomes and scoring decreases in FFM and increases in FM as negative outcomes. The BCCI is the net sum of these calculations. Differences between scale weight changes and BCCI values were subsequently compared to obtain "discordance scores."
Discordance scores ranged from 0.0 lbs. to >30.0 lbs. with a mean absolute value of between the two measures of 7.79 lbs. (99% confidence interval: 7.49-8.10, p <0.00001), SD = 7.4 lbs. Similar discordance scores were also found in subgroups of self-reported gender, ethnicity, and age.
A significant difference of 7.79 lbs. was found between the BCCI and the BMI to evaluate the efficacy of weight loss interventions. If assessing changes in body composition is a treatment goal, use of the BMI could result in significantly erroneous conclusions.
人们普遍认为体重指数（BMI）反映了体脂肪量（FM）的变化。然而，它无法区分所减少或增加的体重类型——体脂肪量（FM）或去脂体重（FFM）。BMI 对待这两种变化是一样的，尽管它们有相反的健康后果。本研究的目的是提出一种更精确的衡量标准，即身体成分变化指数（BCCI），它可以区分 FM 和 FFM 的变化，本研究将其与使用 BMI 作为结果衡量标准进行比较。
从 3870 名在参加各种减肥干预措施时完成基线和研究结束时的双能 X 射线吸收法（DEXA）全身扫描的受试者中获得数据。由于该成年队列的身高保持不变，BMI 的变化与体重秤的变化相对应（r=0.994），允许将 BMI 的变化转换为“磅”，以匹配用于计算 BCCI 的统计数据。BCCI 通过将 FFM（磅）的增加和 FM（磅）的减少评分作为阳性结果，将 FFM 的减少和 FM 的增加评分作为阴性结果进行计算。BCCI 是这些计算的净总和。随后将体重秤的变化与 BCCI 值之间的差异进行比较，以获得“不一致评分”。
不一致评分范围从 0.0 磅到>30.0 磅，两种测量方法之间的平均值绝对值为 7.79 磅（99%置信区间：7.49-8.10，p<0.00001），标准差为 7.4 磅。在自我报告的性别、种族和年龄亚组中也发现了类似的不一致评分。
BCCI 和 BMI 之间发现了 7.79 磅的显著差异，用于评估减肥干预的效果。如果评估身体成分的变化是治疗目标，使用 BMI 可能会导致严重错误的结论。
