# Long-term body composition changes after bariatric surgery and their association with fat- and bone-derived hormones

## TL;DR

This study shows that bariatric surgery leads to significant fat and lean mass loss over 36 months, with greater lean mass loss in women and older adults, and links these changes to fat- and bone-derived hormones.

## Contribution

The study provides a 36-month longitudinal analysis of body composition changes and their hormonal associations after different bariatric procedures.

## Key findings

- RYGB resulted in the highest fat mass loss (46.6%) and significant lean mass loss (14.2%).
- Lean mass loss was significantly greater in surgical groups compared to the diet group, especially after RYGB and LAGB.
- Higher adiponectin and ucOC levels were associated with greater lean mass reduction after adjusting for treatment, age, and sex.

## Abstract

Bariatric surgery effectively reduces obesity-related comorbidities, however fat mass loss is often accompanied by lean mass reduction. This 36-month prospective study (N=55) examined body composition changes following three bariatric procedures compared with a diet-controlled group (Diet).

Random intercept mixed-effects models assessed 36-month trajectories of fat and lean mass, comparing surgical groups with Diet, adjusting for age and sex. Associations between body composition changes, measured by dual-energy X-ray absorptiometry and adiponectin (fat-derived) and undercarboxylated osteocalcin (ucOC; bone-derived) hormones were evaluated at 0, 1, 3, 6, 12, 24, and 36 months.

Roux-en-Y gastric bypass produced the greatest fat mass loss (46.6%), followed by sleeve gastrectomy (30.1%) and laparoscopic adjustable gastric banding (20.5%). Corresponding lean mass losses were 14.2%, 11.7%, and 5.2%. In Diet changes in fat mass (−2.1%) and lean mass (+3.6%) were non-significant. Over 36 months, all surgical groups lost significantly more lean mass than Diet, with the greatest losses after RYGB (15.1%) and LAGB (14.8%). Women experienced 30% greater lean mass loss than men (95% CI: -34%, -26%). Each additional year of age was associated with a 0.2% lean mass decline (95% CI: -0.5%, 0%). After controlling for treatment procedure, age and sex, each twofold increase in adiponectin and ucOC was associated with 5.0% (95% CI: -9.4%, -2.4%) and 3.7% (95% CI: -5.0%, -1.3%) reductions in lean mass, respectively.

These findings underscore the lean mass loss risk after bariatric surgery, particularly in women and older adults, and highlight the importance of long-term monitoring of body composition, nutrition and bone health.

The study was registered as ANZCTR: 12613000188730.

The online version contains supplementary material available at 10.1007/s12020-026-04564-0.