Patterns of Early Weight Loss after Bariatric Surgery: Fat Free Mass Loss versus Fat Mass Loss

• Published in: Obesity (Silver Spring, Md.) Md.), 2023-11, Vol.31, p.243-243
• Main Authors: Standish, Julia, Carlton, Carrie, Mikhailova, Tatiana, Jones, Andrulisa, Rabach, Lauren, Shope, Timothy
• Format: Article
• Language: English
• Subjects: Body composition; Gastrointestinal surgery
• ISSN: 1930-7381; 1930-739X

Background: Bariatric surgery remains the most effective method for weight loss and mitigation of comorbid conditions for obese patients. Early post-operative weight loss is rapid and slowly levels off, creating characteristic asymptotic weight loss curves. Little is known with regard tto the relative degrees of fat free mass (FFM) loss versus fat mass (FM) loss in this early period. Ideally, weight loss methods including bariatric surgery will provide FM loss that is much greater than FFM loss, thus preserving lean body mass. We sought to better characterize the patterns of early weight loss after bariatric surgery. Methods: Retrospective chart review of patients who had bariatric surgery at our institution between March 2019 and November 2022 was performed. A total of 184 patients underwent sleeve gastrectomy (SG), Roux-en-Y gastric bypass (RYGB) or Biliopancreatic Diversion with Duodenal Switch (BPD/DS). Body composition analysis was performed using bioimpedance methods with a medical body composition analyzer. The following values were obtained for each patient: fat free mass (FFM), fat mass (FM) and total weight (WT). Data was collected pre-surgery and in post-surgery follow up at 2 weeks-1 month, 2-4 months and 5-7 months. Results: The highest rates of FFM loss were found in the first 2 weeks post-bariatric surgery (p < 10e-7, 95%CI [10.5-17.9]). FFM and FM loss showed no significant difference within the initial 2 weeks postsurgery (p = 0.74). Following the initial 2 months post-surgery, FFM rates slowed down significantly. FM loss rates continued to progress after the initial 2 weeks compared to FFM loss. Significant differences between FFM and FM loss were seen at 2-4 months (p = 1.0e-09, 95% Cl[5.8-9.1]) and 5-7 months post-surgery (p = 5.1e-08, 95% Cl [1.6-5.5]). The RYGB procedure showed significantly more mean FFM loss within the first 2 weeks compared to patients who underwent SG (RYGB = 7.54, SG = 5.82, p = 0.04678, 95%CI [0.03-3.4]). No difference was seen after this. No other significant differences were seen based on surgical procedure. Long term weight loss is not impacted by early excessive FFM. Conclusions: FFM loss is highest in the first 2 weeks post-surgery. FM loss predominated subsequently. Overall weight loss is not significantly impacted by excessive FFM loss. FFM loss is short-term. Type of procedure only affects early FFM loss.