An observational cohort study of weight- and length-derived anthropometric indicators with body composition at birth and 5 mo: the Healthy Start study

Am J Clin Nutr. 2017 Aug;106(2):559-567. doi: 10.3945/ajcn.116.149617. Epub 2017 Jun 28.


Background: Despite widespread use of weight- and length-based anthropometric indexes as proxies for adiposity, little is known regarding the extent to which they correspond with fat mass (FM) or fat-free mass (FFM) during infancy.Objective: This study aimed to examine associations of 3 derived indicators-weight-for-age z score (WFAZ), weight-for-length score (WFLZ), and body mass index z score (BMIZ)-with FM, percentage of FM, and FFM measured by air-displacement plethysmography during the first 5 mo of life.Design: Applying prospectively collected data from 1027 infants in a Colorado prebirth cohort, we used multivariate regression to evaluate associations between the derived indicators and body composition at birth and at 5 mo, and with change (Δ) during follow-up.Results: At birth, all 3 derived indicators were more strongly associated with FFM than with FM. Each unit of WFAZ corresponded with 0.342 kg FFM (95% CI: 0.331, 0.351 kg FFM), compared with 0.121 kg FM (95% CI: 0.114, 0.128 kg FM) (P < 0.0001); similar trends were observed for WFLZ and BMIZ. By 5 mo, WFLZ and BMIZ were more strongly associated with FM than with FFM, whereas WFAZ correlated similarly with the 2 components of body composition. ΔWFLZ and ΔBMIZ were both more strongly related to ΔFM than to ΔFFM; however, a direct comparison of the 2 indexes with respect to change in the percentage of FM indicated that ΔBMIZ was the optimal proxy of adiposity gain (P < 0.0001, pairwise difference).Conclusions: Weight- and length-based indexes are poor surrogates for newborn adiposity. However, at 5 mo, WFLZ and BMIZ are suitable proxies of FM. When assessing adiposity gain, ΔBMIZ is the best indicator of fat accrual during the first 5 postnatal months. This trial was registered at as NCT02273297.

Keywords: air-displacement plethysmography; body composition; fat mass; fat-free mass; lean mass; neonatal adiposity.

Publication types

  • Observational Study

MeSH terms

  • Adipose Tissue / metabolism*
  • Adiposity*
  • Adult
  • Anthropometry
  • Biomarkers
  • Birth Weight
  • Body Composition*
  • Body Fluid Compartments / metabolism*
  • Body Height
  • Body Mass Index*
  • Body Weight*
  • Cohort Studies
  • Colorado
  • Female
  • Humans
  • Infant
  • Infant, Newborn
  • Male
  • Nutritional Status
  • Obesity / etiology
  • Obesity / metabolism*
  • Plethysmography
  • Pregnancy
  • Weight Gain
  • Young Adult


  • Biomarkers

Associated data