# Longitudinal analysis of body compositions following Roux-en-Y gastric bypass

## TL;DR

This study tracks changes in body composition after gastric bypass surgery, finding significant fat loss but only modest muscle loss.

## Contribution

The study uses automated CT analysis to longitudinally track skeletal muscle, visceral, and subcutaneous fat changes after Roux-en-Y gastric bypass.

## Key findings

- Visceral and subcutaneous fat volumes decreased significantly at 3 and 6 months post-surgery.
- Skeletal muscle volume declined initially but stabilized after 3 months.
- Correlations between skeletal muscle and subcutaneous fat were meaningful, while others were weak.

## Abstract

Roux-en-Y gastric bypass (RYGB) is associated with substantial weight loss and improved obesity-related comorbidities. However, outcomes on body composition, particularly skeletal muscle (SM), visceral adipose tissue (VAT), and subcutaneous adipose tissue (SAT) remain inconsistent due to limitations in measurement techniques.

Evaluate longitudinal changes in SM, VAT, and SAT volumes (cm3) following RYGB using Data Analysis Facilitation Suite (DAFS), an automated computed tomography (CT) analysis software.

In this prospective pilot study, nine female patients underwent low-dose abdominal and pelvic CT imaging at baseline, 3-, and 6-months post-RYGB. Volumetric analysis from the ninth thoracic veterbra (T9) to the sacrum was performed using DAFS. Changes in SM, VAT, and SAT were assessed using paired t-tests.

Participants (mean ± SD; age 35 ± 9 years, BMI 48 ± 10 kg/m²) experienced substantial weight loss (14 ± 5% at 3 months, 25 ± 7% at 6 months; p < 0.001). SAT and VAT volumes decreased significantly by 21% and 27% at 3 months, and by 31% and 47% at 6 months, respectively (all p < 0.001). In contrast, SM volume showed a significant decline of 14% at month 3 (p < 0.001) and then plateaued thereafter.

The changes over time differ substantially among SM, VAT and SAT after Roux-en-Y gastric bypass, reflecting the distinct physiological responses and metabolic improvement of different tissue types. Larger and longer clinical studies are needed to validate these findings.

• RYGB leads to large relative reductions in visceral and subcutaneous adipose tissue (VAT and SAT) volumes at 6 months while skeletal muscle (SM) volume shows a more modest relative decline at 3 months and then stabilizes at 6 months.

• There are meaningful correlations between SM and SAT, whereas the correlations between VAT and SAT, and between SM and VAT, appear weak or negligible.

• Findings suggest RYGB is associated with skeletal muscle preservation relative to fat loss, but larger, longer-term studies are needed to confirm these results and their clinical implications.