Weight-related changes in MRI-derived measures of body composition and liver steatosis: a large-scale analysis for obesity trial design.

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 = 3070) 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), total skeletal muscle volume (SM, or indexed SM), muscle 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 = 3070, age 63 years, male 49%, 13% with obesity, 43% with overweight). Moderate or large weight gain increased LFC, VAT, SAT, MFISM, and SM (all p < 0.001). Weight loss also occurred in 28%. Decreases were observed with moderate or large weight loss in LFC, VAT, SAT, SM, SMI, and psoas CSA (all p < 0.001). MFISM was reduced with large weight loss. For VAT and liver fat, prevalent type 2 diabetes exacerbated weight gain-related increases, and blood pressure medication attenuated the impact of weight change. For individuals with overweight or obesity, for every 5% drop in weight, there was 16% reduction in VAT, 11% in SAT, 24% in liver fat, 2.3% in MFISM, 1.5% in SM (or 1.4% in SMI) and 2.1% in psoas CSA. 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. Weight changes affect body composition and liver fat and can inform obesity trial design.