Age-related changes in basal substrate oxidation and visceral adiposity and their association with metabolic syndrome

Purpose: Ageing is directly associated with visceral fat (VAT) deposition and decline of metabolically active cellular mass, which may determine age-related shifts in substrate oxidation and increased cardiometabolic risk. We tested whether VAT and fasting respiratory quotient (RQ, an index of macronutrient oxidation) changed with age and if they were associated with increased risk of metabolic syndrome (MetSyn). Methods: A total of 2819 adult participants (age range: 18–81 years; men/women: 894/1925) were included; we collected history, anthropometric measures, biochemistry, smoking habits, and physical activity. The body mass index range was 18.5–60.2 kg/m2. Gas exchanges (VO2 and VCO2) were measured by indirect calorimetry in fasting conditions, and RQ was calculated. Body composition was measured by bioelectrical impedance. Abdominal subcutaneous fat and VAT were measured by ultrasonography. MetSyn was diagnosed using harmonised international criteria. Multivariate linear and logistic regression models were utilised. Results: VAT increased with age in both men (r = 0.31, p < 0.001) and women (r = 0.37, p < 0.001). Basal RQ was not significantly associated with age (p = 0.49) and VAT (p = 0.20); in addition, basal RQ was not a significant predictor of MetSyn (OR 3.31, 0.57–19.08, p = 0.27). VAT was the primary predictor of MetSyn risk in a fully adjusted logistic model (OR 4.25, 3.01–5.99, p < 0.001). Conclusions: Visceral adiposity remains one of the most important risk factors for cardiometabolic risk and is a significant predictor of MetSyn. Post-absorptive substrate oxidation does not appear to play a significant role in age-related changes in body composition and cardiometabolic risk, except for a correlation with triglyceride concentration.