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

Sani M Roy¹, David A Fields², Jonathan A Mitchell³

¹Division of Endocrinology and Diabetes, Cook Children's Medical Center, Fort Worth, TX; Division of Endocrinology and Diabetes, The Children's Hospital of Philadelphia, Philadelphia, PA.

The Journal of Pediatrics

|October 1, 2018

Insights

Body mass index (BMI) is a superior measure of infant adiposity at one month compared to weight-for-length (WFL). This study highlights BMI

Area of Science:

Pediatric Nutrition
Infant Growth Assessment
Body Composition Analysis

Background:

Accurate assessment of infant adiposity is crucial for monitoring growth and nutritional status.
Traditional metrics like weight-for-length (WFL) may not fully capture body composition in early infancy.
Emerging research explores the utility of body mass index (BMI) in this age group.

Purpose of the Study:

To compare the effectiveness of body mass index (BMI) versus weight-for-length (WFL) in assessing measured adiposity in one-month-old infants.
To determine which anthropometric measure, BMI or WFL, better correlates with detailed body composition parameters.

Main Methods:

Utilized data from two infant cohorts (n=146 and n=147) with measured length, weight, and body composition via air displacement plethysmography at one month.
Calculated World Health Organization-based BMI and WFL z-scores.
Employed correlation and multiple linear regression analyses, adjusted for birth weight, to assess associations between BMI-Z, WFL-Z, and various body composition z-scores (e.g., fat mass-Z, fat-free mass-Z).

Main Results:

Both BMI-Z and WFL-Z were significantly associated with fat mass and related body composition outcomes.
BMI-Z demonstrated stronger associations with fat mass-Z, fat mass/length^2-Z, and fat mass/length^3-Z compared to WFL-Z (P < .05).
These stronger associations for BMI-Z persisted across the distribution of body composition outcomes, even after adjusting for birth weight.

Conclusions:

Body mass index (BMI) serves as a more accurate indicator of adiposity in early infancy than weight-for-length (WFL).
The findings support the preferential use of BMI for assessing growth and nutritional status in infants.
This evidence aids in refining infant growth monitoring guidelines.

Read full analysis

Abstract

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/length²-Z, fat mass/length³-Z, fat-free mass-Z, and fat-free mass/length²-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/L²-Z (0.73 and 0.51), and FM/L³-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.

Keywords:

adiposity air displacement plethysmography infancy infant obesity

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