Supplementary information for The proportion of weight gain due to change in fat mass in infants with vs without rapid growth

Article abstractBackground: There is extensive evidence that rapid infant weight gain increases the risk of childhood obesity, but this is normally based on childhood body mass index (BMI) only and whether or not this is because infants with rapid weight gain accrue greater fat mass is unknown.Objective: The primary objective of our study was to test whether the proportion of infant weight gain due to concurrent increases in fat mass is greater in infants with rapid weight gain as compared to those with normal growth.Methods: Body composition was assessed by 1) air-displacement plethysmography (ADP) at 0 & 6 months in 342 infants from Australia, India, and South Africa and 2) deuterium dilution (DD) at 3 & 24 months in 555 infants from Brazil, Pakistan, South Africa, and Sri Lanka. Weight gain and length growth were each categorized as slow, normal, or rapid using cut-offs of < -0.67 or >+0.67 Z-scores. Regression was used to estimate and contrast the percentages of weight change due to fat mass change.Results: Approximately 40% of the average weight gain between 0-6 months and 20% of the average weight gain between 3-24 months was due to increase in fat mass. In both samples, compared to the normal group, the proportion of weight gain due to fat mass was higher on average among infants with rapid weight gain and lower among infants with slow weight gain, with considerable individual variability. Conversely, slow and rapid length growth was not associated with differential gains in fat mass.Conclusions: Pediatricians should monitor infant growth with the understanding that, while crossing upward through the weight centiles generally is accompanied by greater adiposity gains (not just higher BMI), upward crossing through the length centiles is not.

文章摘要
研究背景：现有大量证据表明，婴儿期体重快速增长会升高儿童期肥胖风险，但此类结论通常仅以儿童体质指数（Body Mass Index, BMI）为评估依据，目前尚不明确该关联是否源于体重快速增长的婴儿其脂肪量积累更多。
研究目的：本研究的主要目标为验证，与正常生长的婴儿相比，体重快速增长的婴儿其体重增长中由脂肪量同步增长所贡献的比例是否更高。
研究方法：一是对来自澳大利亚、印度及南非的342名婴儿，于出生后0月龄和6月龄时采用空气置换体积描记法（air-displacement plethysmography, ADP）评估身体成分；二是对来自巴西、巴基斯坦、南非及斯里兰卡的555名婴儿，于3月龄和24月龄时采用氘稀释法（deuterium dilution, DD）评估身体成分。以＜-0.67或＞+0.67的Z评分（Z-score）临界值为标准，将体重增长与身长增长分别归类为缓慢、正常或快速。通过回归分析估算并对比由脂肪量变化所导致的体重变化百分比。
研究结果：0~6月龄期间的平均体重增长中，约40%源于脂肪量增加；3~24月龄期间的平均体重增长中，约20%源于脂肪量增加。在两个研究队列中，与正常生长组相比，体重快速增长的婴儿其体重增长中由脂肪量贡献的比例平均更高，而体重缓慢增长的婴儿该比例则更低，且存在较大的个体差异。与之相反，身长增长缓慢或快速均与脂肪量的差异化增长无关联。
研究结论：儿科医师在监测婴儿生长情况时应明确，尽管体重百分位向上跨越通常伴随更多的脂肪量积累（而非仅体质指数升高），但身长百分位向上跨越则无此关联。