Body Mass Index Is a Better Indicator of Body Composition than Weight-for-Length at Age 1 Month

Sani M. Roy, David A. Fields, Jonathan A. Mitchell, Colin P. Hawkes, Andrea Kelly, Gary D. Wu, Patricia A. DeRusso, Michal A. Elovitz, Eileen Ford, Danielle Drigo, Babette S. Zemel, Shana E. McCormack

Research output: Contribution to journalArticlepeer-review

27 Scopus citations


Objective: To assess whether body mass index (BMI) provides a better assessment of measured adiposity at age 1 month compared with weight-for-length (WFL). Study design: Participants were healthy term-born infants in the Infant Growth and Microbiome (n = 146) and the Baby Peas (n = 147) studies. Length, weight, and body composition by air displacement plethysmography were measured at 1 month. World Health Organization-based WFL and BMI z-scores were calculated. Within-cohort z-scores of percent fat-Z, fat mass-Z, fat mass/length 2 -Z, fat mass/length 3 -Z, fat-free mass-Z, and fat-free mass/length 2 -Z were calculated. Correlation and multiple linear regression (adjusted for birth weight) analyses tested the associations between body composition outcomes and BMI-Z vs WFL-Z. Quantile regression was used to test the stability of these associations across the distribution of body compositions. Results: The sample was 52% female and 56% African American. Accounting for birth weight, both BMI-Z and WFL-Z were strongly associated with fat mass-Z (coefficients 0.56 and 0.35, respectively), FM/L 2 -Z (0.73 and 0.51), and FM/L 3 -Z (0.79 and 0.58), with stronger associations for BMI-Z compared with WFL-Z (P <.05). Even after accounting statistically for birth weight, BMI-Z was persistently more strongly associated than WFL-Z with body composition outcomes across the distribution of body composition outcomes. Conclusions: We demonstrate in 2 distinct cohorts that BMI is a better indicator of adiposity in early infancy compared with WFL. Our findings support the preferred use of BMI for growth and nutritional status assessment in infancy.

Original languageEnglish
Pages (from-to)77-83.e1
JournalJournal of Pediatrics
StatePublished - Jan 2019
Externally publishedYes


  • adiposity
  • air displacement plethysmography
  • infancy
  • infant
  • obesity


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