Defining BMI cutoff points for detecting excess body fat in young adults

Area of Science:

• Human Physiology
• Anthropometry
• Public Health

Background:

• Traditional body mass index (BMI) cutoffs for overweight and obesity may not accurately identify excess body fat in young adults.
• Accurate assessment of body fat is crucial for early detection of health risks associated with adiposity.

Purpose of the Study:

• To establish new BMI cutoff points for detecting excess body fat in 18-year-old males and females.
• To compare the accuracy of proposed BMI cutoffs with traditional thresholds using air displacement plethysmography (ADP) as a reference.

Main Methods:

• Cross-sectional analysis of the 2004 Pelotas Birth Cohort (Brazil) with 3052 participants at age 18.
• Body composition measured by ADP; excess adiposity defined as ≥20% fat mass in males and ≥33% in females.
• Receiver operating characteristic (ROC) curve analysis and Youden index used to determine optimal BMI cutoffs.

Main Results:

• Optimal BMI cutoffs were ≥24.0 kg/m² for males and ≥23.5 kg/m² for females.
• New cutoffs demonstrated significantly higher sensitivity in detecting excess body fat compared to the traditional obesity cutoff (≥30.0 kg/m²).
• The ≥30.0 kg/m² cutoff identified less than one-third of individuals with excess body fat.

Conclusions:

• Newly proposed BMI cutoffs (≥24.0 kg/m² males, ≥23.5 kg/m² females) are more effective for detecting excess body fat in young adults.
• These optimized cutoffs can facilitate earlier identification of adiposity.
• Findings support the implementation of targeted public health interventions for obesity prevention.