| Description | Background/Objectives: Amid rising global obesity rates and advances in weight-loss therapies, monitoring body composition and ectopic fat could refine trial design. We quantified weight-related changes in body composition and liver steatosis prior to widespread adoption of incretin treatments. Subjects/Methods: Adults (N=3,071) from the UK Biobank with repeat abdominal MRI scans were included. Percent weight change from baseline was categorised: stable (0±2%), mild change (2-5% weight gain/loss), moderate change (5-10% weight gain/loss), or large change (10-15% weight gain/loss). Intervention/Methods: MRI data were processed automatically from two visits, spaced 2.7 years apart, to derive volumetric visceral (VAT), subcutaneous adipose tissue (SAT), skeletal muscle volume (SM, or indexed SM), fat infiltration (MFISM), and psoas muscle cross-sectional area (CSA) in the abdominal region. Liver fat content (LFC) was assessed using LiverMultiScan. Dual-energy x-ray absorptiometry (DXA) measurements were compared. Results: Weight gain occurred in 28% of all subjects (N=3071, age 63 years, male 49%, 13% with obesity, 43% with overweight). Moderate or large weight gain increased LFC, VAT, SAT, MFISM and psoas CSA (all p<.001). Weight loss also occurred in 28%. Decreases were observed with moderate or large weight loss: LFC -20% or -33%, VAT -22 or -38%, SAT -17 or -30%, SM -3 or -5%, SMI -3 or -4%, psoas CSA -4 or -5%, respectively (all p<.001). MFISM reduced with large weight loss, by -4%. For every 5% drop in weight, there was -16% reduction in VAT, -11% in SAT, -24% in liver fat, -1.5% in SM (or -1.4% in SMI) and -2.1% in psoas muscle, in those with obesity or overweight. DXA changes in lean mass correlated weakly with changes in SM volume (rho 0.28-0.47). Conclusions: Using MRI, relative changes in body composition and liver steatosis resulting from weight loss can inform clinical trials, including placebo arm design and power estimations. |
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