Adiposity rebound is misclassified by BMI rebound

Area of Science:

• Pediatric endocrinology
• Childhood obesity research
• Body composition analysis

Background:

• Adiposity rebound (AR) is the nadir of body mass index (BMI) percentiles between ages 3-7.
• Early AR is a risk factor for childhood obesity, making it a target for prevention.
• BMI does not fully represent body composition, necessitating investigation of fat mass index (FMI) and fat-free mass index (FFMI).

Purpose of the Study:

• To investigate the rebound patterns of FMI and FFMI alongside BMI in children.
• To determine if AR, as defined by BMI, accurately reflects changes in body fat.

Main Methods:

• Pooled cross-sectional data from 19,264 children aged 3-11 years from three German studies.
• Height and weight measurements were taken.
• Fat mass (FM) and fat-free mass (FFM) were determined using bioelectrical impedance analysis and analyzed with a population-specific algorithm. BMI, FMI, and FFMI percentiles were constructed using the LMS method.

Main Results:

• Both BMI and FMI percentiles exhibited a rebound, while FFMI percentiles showed a consistent increase with age.
• FMI rebound occurred approximately 1.6-1.8 years later than BMI rebound on the 90th percentile (P90) in both boys and girls.
• At AR, the increase in BMI-P90 slope was primarily driven by FFMI, not FMI. Conversely, at FMI rebound, the BMI slope was strongly correlated with FMI.

Conclusions:

• BMI rebound does not equate to fat mass rebound.
• The increase in BMI during AR is influenced by fat-free mass, not fat mass.
• Adiposity rebound should be redefined based on fat mass index rebound rather than BMI rebound for more accurate obesity risk assessment and prevention.