Body composition and energy metabolism following Roux-en-Y gastric bypass surgery

Abstract

Roux-en-Y gastric bypass (RYGB) surgery has become an accepted treatment for excessive obesity. We conducted a longitudinal study to assess regional body composition, muscle proteolysis, and energy expenditure before RYGB, and 6 and 12 months after RYGB. Whole-body and regional fat mass (FM) and lean mass (LM) were assessed via dual energy X-ray absorptiometry (DXA), and myofibrillar protein degradation was estimated by urinary 3-methylhistidine (3-MeH) in 29 subjects. Energy expenditure and substrate oxidation were also determined using a whole-room, indirect calorimeter in 12 of these subjects. LM loss constituted 27.8 +/- 10.2% of total weight loss achieved 12 months postoperatively, with the majority of LM loss (18 +/- 6% of initial LM) occurring in the first 6 months following RYGB. During this period, the trunk region contributed 66% of whole-body LM loss. LM loss occurred in the first 6 months after RYGB despite decreased muscle protein breakdown, as indicated by a decrease in 3-MeH concentrations and muscle fractional breakdown rates. Sleep energy expenditure (SEE) decreased from 2,092 +/- 342 kcal/d at baseline to 1,495 +/- 190 kcal/day at 6 months after RYGB (P < 0.0001). Changes in both LM and FM had an effect on the reduction in SEE (P < 0.001 and P = 0.005, respectively). These studies suggest that loss of LM after RYGB is significant and strategies to maintain LM after surgery should be explored.

Figure 1

Whole-body fat and lean tissue before and after gastric bypass surgery. (a) Percent body fat (closed circles) and lean (open squares) tissue and (b) fat (closed circles) and lean (open squares) tissue mass at baseline (time 0 months), and at 6 and 12 months after surgery. Values are mean ± s.d. *P < 0.0001, baseline vs. 6 months and 6 months vs. 12 months.

Figure 2

Changes in regional fat and lean tissue mass after gastric bypass surgery. Data are expressed as mean ± s.d. for fat (closed circles) and lean (open squares) tissue mass in the (a) extremities, (b) trunk, (c) abdomen, and (d) nonabdominal trunk at baseline (time 0 months), and at 6 and 12 months after surgery. ^*P < 0.0001 and ^#P = 0.006, baseline vs. 6 months and 6 months vs. 12 months.

Figure 3

Estimates of muscle tissue breakdown with Roux-en-Y gastric bypass surgery. (a) 24-h 3-methylhistidine (3-MeH) levels, (b) amount of 3-MeH per kg of lean mass, and (c) fractional breakdown rate of muscle at baseline (time 0 months), and at 6 and 12 months after surgery. Data are expressed as mean ± s.d. ^*P < 0.005, ^**P < 0.0001, and ^#P < 0.05, baseline vs. 6 months and 6 months vs. 12 months.