Causes of significant and early loss of FFM after bariatric surgery

There is a significant and early loss of fat-free mass (FFM) in patients with severe obesity who undergo bariatric surgery, which is not related to the parameters of protein metabolism or the surgical technique used, suggesting the existence of an independent mechanism, according to researchers from Vall d’Hebron Institut de Recerca (VHIR), Universitat Autònoma de Barcelona, Barcelona, Spain. The outcomes were reported in the paper, ‘The Impact of Bariatric Surgery on the Muscle Mass in Patients with Obesity: 2-Year Follow-up’, published in Obesity Surgery.

Although bariatric surgery can result significant and sustained weight loss, it can also contribute to the loss of FFM. However, according to the study’s authors, there is a paucity of data in the literature regarding the impact of surgery on FFM. Therefore, they set out to evaluate the impact of surgery on the FFM and assessed body composition by bioimpedance (BIA). This study was part of the larger PREDIBAR trial.

In their prospective, observational study, 85 consecutive patients with severe obesity who had surgery underwent complete medical history, physical and anthropometric evaluation, and body composition assessment by means of BIA (using Bodystat QuadScan4000) at baseline, one, six, 12, and 24 months.


The majority of patients were female (72.9%), average age was 45.54±9.98 years and pre-surgery BMI was 43.87±6.52 kg/m2. Patients with T2D were treated with diet (100%), metformin (90%), aGLP-1 (62.4%), iSGLT-2 (13.2%), iDPP4 (45.1%) and insulin (2.3%). For the calculation of HOMA-IR, the patients treated with insulin were excluded. All the patients presented remission of T2D, according to ADA guidelines after the surgery and was maintained at 24 months.

The researchers reported that FFM significantly decreased one month after surgery and this continued out to 24 months. Fat mass also significantly decreased from month one out to month 12. Between months 12 and 24 after the BS, FM stabilised and presented a slight tendency to increase, although without reaching statistical significance.

Basal metabolism rate (BMR), measured by BIA, significantly decreased one month after surgery and continued to decrease during the follow-up. The researchers reported a positive correlation between FFM and the BMR at all timepoints, respectively. However, FM showed no relation with the BMR.

Of the two procedures, RYGB was associated with greater global EWL and TWL than SG, although no significant differences were seen between the two techniques in terms of body composition and biochemical analysis (HOMA-IR and transthyretin), except for the phase angle (PA, an interpretation of the muscle cell’s capacity to transmit the electrical current produced by the BIA device according to the cell’s quality) that was significantly lower after the RYGB. They also identified significantly lower levels of PA after surgery in all patients, compared to data in the literature from subjects with normal weight, of similar age and gender.

The multiple regression analysis revealed that HOMA-IR and baseline FFM were the only independent predictors of FFM at 24 months surgery. The logistic regression analysis showed the important loss of FFM after surgery was independent of the age, gender, protein metabolism or surgical technique. Indeed, only pre-surgical FFM and pre-BS HOMA-IR were associated with the FFM at 24 months after surgery. This, the authors suggest, indicates that pre-surgical conditions have an important influence on the evolution post-surgery.

“These findings point to the urgent need to take into consideration changing the actual clinical guidelines for the management of patients with obesity, especially those that are candidate for bariatric surgery, by incorporating body composition studies (both quantitative and qualitative) in the routinary preoperatory and follow-up evaluations,” they stressed. “BIA is a rapid, reliable, repeatable, and non-expensive test that can be easily implemented in the daily clinical practice, as part of the evaluation of patients with obesity. This action will allow to implement more personalized approach, and design-specific physical exercises, diet, and pharmacological therapy aimed at improving the pre-bariatric surgery muscle mass and insulin resistance.”

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