BACKGROUND: Insulin resistance is associated with the higher content of intermuscular adipose tissue (IMAT) and the saturation of intramyocellular lipid (IMCL), but a paucity of data exist in humans. This study examined associations among IMAT content, IMCL saturation, and fasting glucose concentration in middle-aged and older adults with overweight or obesity. METHODS: Seventy-five subjects (26 males, 49 females) were recruited and thigh muscle and IMAT were assessed using magnetic resonance imaging. Vastus lateralis tissue was acquired from a subset of nine subjects and IMCL content and saturation were assessed using nonlinear dual complex microscopy. RESULTS: The characteristics of the 75 subjects were as follows: age 59±11 years, body mass index 30±5 kg/m², fasting glucose concentration 5.2±0.5 mmol/L, fasting insulin concentration 12.2±7.3 µU/mL, fasting homeostatic model assessment of insulin resistance (HOMA-IR) 2.9±2.0 (mean±SD). IMAT to muscle tissue (MT) volume ratio was positively associated with the saturated fatty acid to unsaturated fatty acid ratio in IMCL. IMAT:MT was positively associated with fasting glucose concentration and HOMA-IR. IMCL saturation was positively associated with fasting glucose concentration while muscle cell area, IMCL area, and % IMCL in muscle cell were not associated with fasting glucose concentration. CONCLUSION: These results indicate that higher intermuscular fat content and IMCL saturation may impact fasting glucose concentration in middle-aged and older adults with overweight or obesity. The centralization of adipose tissue in the appendicular region of the body may promote insulin resistance.
Adipose Tissue* ; Adult* ; Body Mass Index ; Fasting ; Glucose* ; Homeostasis* ; Humans ; Insulin ; Insulin Resistance ; Magnetic Resonance Imaging ; Male ; Microscopy ; Muscle Cells ; Obesity ; Overweight ; Quadriceps Muscle ; Thigh