Sex-specific CT-derived reference cutoffs for body composition in healthy Brazilian adults: a multicenter study

Computed tomography (CT) enables accurate assessment of skeletal muscle and adipose tissue; however, population-specific reference values remain limited. This multicenter cross-sectional study established sex- and region-specific CT-derived reference cutoff values for body composition based on a young normal-BMI reference subgroup from a Brazilian multicenter cohort. A total of 1,621 adults (818 males, 803 females) were included. The cutoffs were derived from a reference subgroup of 650 individuals aged 18-39 years with a BMI of 18.5-24.9 kg/m². Noncontrast CT scans at the third lumbar vertebra were analyzed to quantify the skeletal muscle area (SMA), skeletal muscle density (SMD), and adipose compartments. Cutoffs were defined as 1 or 2 standard deviations below the mean for muscle and above the mean for adiposity, calculated by sex; additional region-specific cutoffs were provided owing to between-region differences. Muscle parameters, particularly SMD, decrease with age, whereas adiposity, especially visceral adipose tissue, increases. Males consistently presented higher muscle indices than females did. The low muscle cutoff values were as follows: SMA < 149 cm², SMI < 49 cm²/m², and SMD < 42 HU in males and SMA < 98 cm², SMI < 38 cm²/m², and SMD < 38 HU in females. High visceral adiposity was > 151 cm² in males and > 90 cm² in females. These findings provide standardized CT-based reference values to support clinical and research assessments.