BMI and Bioelectrical Impedance Analysis: Body Composition Assessment Identifying Elevated Body Fat in Normal-Weight...

Area of Science:

• Nutritional Science
• Body Composition Analysis
• Public Health

Background:

• Body mass index (BMI) is a common but limited measure of nutritional status, failing to differentiate fat from lean mass.
• This limitation can obscure excess adiposity and distort diet-body composition relationships, particularly in young adults.
• Bioelectrical impedance analysis (BIA) offers detailed body composition metrics like percent body fat (PBF) and skeletal muscle mass (SMM).

Purpose of the Study:

• To investigate how integrating BMI with BIA-derived adiposity classifications impacts the assessment of diet-body composition associations in young adults.
• To determine the prevalence of individuals with normal BMI but high PBF.
• To evaluate the relationship between physical activity and body composition markers.

Main Methods:

• A cross-sectional study involving 285 young adults (median age 18 years).
• Participants were classified using both BMI and InBody BIA (measuring PBF).
• Dietary habits were assessed via food frequency questionnaires; statistical analyses included Mann-Whitney U tests and Spearman's rank correlation.

Main Results:

• 12.3% of participants had normal BMI but elevated PBF, a phenotype missed by BMI alone; overall BMI-PBF agreement was 75.4%.
• Physical activity significantly correlated with PBF and SMM, but not BMI.
• Apparent inverse associations between BMI and sweets consumption likely stemmed from reporting bias, disappearing when using PBF.

Conclusions:

• Combining BIA with BMI enhances the detection of elevated body fat, identifying individuals missed by BMI screening alone.
• BIA provides valuable complementary data to BMI for assessing body composition and physical activity relationships.
• Diet-BMI associations may be unreliable due to adiposity misclassification and reporting biases.