Longitudinal Changes in Various BMI Metrics and Adiposity in 3- to 7-Year-Olds

Area of Science:

• Pediatrics
• Childhood Obesity
• Growth Monitoring

Background:

• Body Mass Index z-score (BMIz) is commonly used to track weight changes in children.
• However, BMIz may not accurately reflect changes in body fatness (adiposity).
• Accurate assessment of adiposity is crucial for effective weight management in pediatric populations.

Purpose of the Study:

• To compare the effectiveness of three Body Mass Index (BMI) metrics in assessing changes in adiposity among young children.
• To determine if BMI percentiles are superior to BMI z-score for monitoring body fatness changes.
• To identify the optimal BMI metric for pediatricians to use in assessing a child's body fatness trajectory.

Main Methods:

• A longitudinal study involving 343 children aged 3 years, with serial measurements every 4 months for 4 years.
• Body fatness was measured using dual-energy-x-ray absorptiometry (DXA).
• Changes in body fatness were correlated with changes in three BMI metrics: BMI z-score (BMIz), percentage of the 50th percentile (%50th), and percentage of the 95th percentile (%95th) from CDC growth charts.

Main Results:

• Changes in body fatness showed a stronger association with %50th and %95th compared to BMIz.
• Correlations with %body fat were r = 0.64 for BMIz versus r = 0.77–0.78 for %50th and %95th (P < .001).
• These findings were consistent across different sexes, ethnicities (Black and white children), and weight status (obese and non-obese).

Conclusions:

• Expressing BMI changes as a percentage of the 50th or 95th percentile is a more effective method for capturing adiposity changes in young children than using BMI z-score.
• This improved metric can assist pediatricians in more accurately assessing a child's body fatness progression over time.
• Utilizing the optimal BMI metric enhances clinical decision-making in pediatric weight management programs.