Visceral Adipose Tissue
Fat stored around internal abdominal organs, metabolically active and strongly associated with type 2 diabetes, cardiovascular disease, and metabolic syndrome. GLP-1 receptor agonists and tirzepatide produce preferential visceral fat loss. Tesamorelin specifically targets visceral fat in HIV lipodystrophy.
Technical Context
VAT is measured by: CT scan at L4-L5 level (gold standard — quantitative measurement of VAT area in cm²), MRI (similar accuracy without radiation), DEXA (whole-body composition with regional fat estimates), and waist circumference (clinical proxy — threshold values: >102cm/40in men, >88cm/35in women for elevated risk). VAT is metabolically active: it secretes pro-inflammatory adipokines (TNF-α, IL-6, MCP-1), contributes to hepatic insulin resistance through portal delivery of free fatty acids, and produces less adiponectin (an insulin-sensitising adipokine) than subcutaneous fat. GLP-1 RAs produce preferential VAT reduction relative to lean mass — body composition studies (DEXA and MRI) in semaglutide and tirzepatide trials show that approximately 30-40% of weight lost is lean mass and 60-70% is fat mass, with disproportionate VAT reduction.