Associations between indices of body composition and metabolic status in normal-weight adults: a cross-sectional study of the Tehran Lipid and Glucose Study.

The prevalence of metabolically unhealthy normal weight (MUHNW) was 19.4% among normal-weight adults, with higher prevalence in men than women.

• Study included 1298 adults (40.5% men, 59.5% women) aged 18-80 years with BMI 18.5-24.9 kg/m²
• MUHNW prevalence was 19.4% overall, with sex difference significant at p<0.001
• Data were drawn from phase VII (2019-2021) of the Tehran Lipid and Glucose Study
• Participants were classified as metabolically healthy normal weight (MHNW) or metabolically unhealthy normal weight (MUHNW)

MUHNW participants were significantly older than MHNW participants.

• Mean age of MUHNW participants was 44.5 ± 13.2 years versus 35.8 ± 12.1 years for MHNW participants
• Difference was statistically significant (p<0.001)
• Overall mean age of the study population was 37.5 ± 12.8 years

WHR was the strongest predictor of MUHNW status in both men and women.

• In men, WHR was associated with MUHNW with OR 1.52 (95% CI 1.20 to 1.93)
• In women, WHR was associated with MUHNW with OR 1.31 (95% CI 1.07 to 1.61)
• Logistic regression models were adjusted for age, smoking, and physical activity
• WHR was highlighted as particularly valuable for identifying at-risk individuals where advanced body composition tools are unavailable

Skeletal muscle mass percentage (SMM%) was a protective factor against MUHNW status in men but not reported as significant in women.

• In men, higher SMM% was associated with lower odds of MUHNW: OR 0.90 (95% CI 0.84 to 0.96)
• The protective association of SMM% was specific to men
• SMM% was assessed using bioelectrical impedance analysis

Adjusted mean values of BMI, waist circumference, WHR, fat mass, body fat percentage, fat-to-muscle mass ratio, and fat mass index were all higher in MUHNW compared to MHNW participants in both sexes.

• Differences were observed in both men and women after adjustment for age, smoking, and physical activity
• Body composition was assessed by bioelectrical impedance analysis
• Anthropometric measures included waist circumference (WC) and waist-to-hip ratio (WHR)
• Body composition indices included fat mass (FM), body fat percentage (BFP), fat mass index (FMI), fat-free mass index, skeletal muscle indices, and fat-to-muscle mass ratio (FMR)

BMI, waist circumference, WHR, and body fat indices were all positively associated with metabolically unhealthy status among normal-weight adults of both sexes.

• Associations were examined using logistic regression adjusted for age, smoking, and physical activity
• Both anthropometric and bioelectrical impedance-derived body composition indices showed positive associations with MUHNW
• The study design was cross-sectional, limiting causal inference