Introduction:

Body Mass Index (BMI) is a widely used but imprecise measure of obesity. Bioelectric impedance analysis (BIA) offers a more accurate body composition assessment, including fat mass and percentage adiposity. This study aimed to compare obesity classification using BMI versus BIA-derived % adiposity in a Obesity diagnosis setting.

Methods:

1. Setting: Weight management clinic
2. BMI Classification:
   1. Obese: ≥30 kg/m²
   2. Overweight: 25–29.9 kg/m²
   3. Normal: 18.6–24.9 kg/m²
3. BIA Classification of Obesity:
   1. Women: % adiposity ≥33%
   2. Men: % adiposity >25%
4. Body Composition Tool: TANITA BIA scale (MC-780U)
5. Body composition measures: total body water, fat, muscle and bone mass, and % adiposity
6. Comparison: Concordance between BMI- and BIA-based obesity diagnosis

Results: Among the 112 patients:

1. Demographics: 87% female
   1. 49% non-Hispanic white
   2. 43% Black
   3. Mean age: 49 ± 13 years
2. Anthropometrics:
   1. Mean BMI: 36.4 ± 7.7 kg/m²
   2. Mean % adiposity: 40.3 ± 8.2%
3. Obesity Classification:
   1. By BMI: 81.2% obese (n=91), 12.5% overweight (n=14), 6.2% normal weight (n=7)
   2. By BIA: 83.9% obese (n=94)
4. Concordance: 87.5% agreement (n=98) between BMI and BIA
5. Discordant Cases: Total: 14
   1. 86% female (n=12), 64% aged 39–59 years
   2. 8 patients: Obese by BIA but not BMI
   3. 6 patients: Obese by BMI but not BIA

Conclusion:

BIA-based assessment provides a more accurate evaluation of body fat and improves obesity classification over BMI alone. The 12.5% discordance between the two methods suggests potential misclassification of obesity status, which could lead to over- or underestimation of associated health risks.

ADA 2025, 20-23 June, Chicago