Body mass index (BMI) — calculated as weight (kg) / height² (m²) — is the most widely used clinical screening measure for overweight and obesity but is a notoriously poor measure of metabolic health or disease risk at the individual level. BMI is a population-level screening tool that misclassifies approximately 30% of individuals as healthy based on BMI when they have metabolically unhealthy body composition (high visceral fat, low muscle mass — "normal weight obesity" or "metabolically obese normal weight"). Conversely, muscular individuals are frequently misclassified as overweight or obese by BMI. Evidence-based body composition assessment provides the clinically meaningful information that BMI cannot. Our diagnostic equipment section includes body composition assessment tools for clinical use.
DEXA: The Clinical Gold Standard
Dual-energy X-ray absorptiometry (DEXA) body composition scanning is the clinical gold standard for: total lean mass and fat mass quantification by body region; appendicular skeletal muscle mass index (ASMI) — the primary diagnostic criterion for sarcopenia (European Working Group on Sarcopenia in Older People, 2019); visceral adipose tissue (VAT) quantification — the metabolically active fat depot most strongly associated with insulin resistance and cardiovascular risk; and bone mineral density (BMD) for osteoporosis assessment. DEXA exposure is minimal (equivalent to a few hours of background radiation) and clinically appropriate for sarcopenia screening (over 60), obesity management programs (tracking lean preservation during weight loss), and post-bariatric surgery monitoring. Precision: coefficient of variation 1–2% for lean mass, making it sensitive enough to detect clinically meaningful changes.
Bioelectrical Impedance Analysis (BIA)
BIA measures body composition by passing a weak electrical current through the body — fat tissue has higher electrical resistance than lean tissue, allowing fat/lean estimation from resistance and reactance measurements. BIA devices range from consumer hand-held units (accuracy: moderate, affected by hydration status) to clinical multi-frequency BIA systems (Tanita, InBody, Seca) with substantially higher accuracy approaching DEXA agreement in controlled conditions. Clinical BIA in standardized conditions (48-hour alcohol avoidance, 4-hour fasting, standard hydration protocol) achieves acceptable precision for serial measurement — monitoring body composition changes over time in weight management programs, oncology nutritional monitoring, and sarcopenia tracking. Segmental BIA (measuring each body segment separately) provides the most detailed information and reduces error compared to whole-body single-site measurement. Clinical-grade BIA scales from Tanita and InBody are available through our diagnostic equipment section.
