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Body Composition Changes Following Sleeve Gastrectomy Vs. One-Anastomosis Gastric Bypass: Tehran Obesity Treatment Study (TOTS)



This study aimed to evaluate body composition changes and the determinants of fat-free mass loss (FFML) up to 3 years after sleeve gastrectomy (SG) and one-anastomosis gastric bypass (OAGB).

Materials and Methods

A prospective study was conducted on 3864 patients with severe obesity who underwent either SG (2746, 76.1% women, mean age: 39.2 ± 11.6 years, and BMI: 44.3 ± 5.6 kg/m2) or OAGB (1118, 82.2% women, age: 39.9 ± 10.7 years, BMI: 45.6 ± 6.3 kg/m2). Body composition parameters were measured by bioelectrical impedance analysis preoperatively and 1, 3, 6, 9, 12, 18, 24, and 36 months after surgery. Changes in body composition were assessed using the propensity matched generalized estimated equation (GEE) method. The determinants of fat-free mass loss/weight loss (FFML/WL%) were defined using a mixed-model GEE analysis.


Means of FM, FFM, and FFML/WL% decreased significantly in both study groups (Ptrend < 0.001). Changes in BMI, EWL%, FM, and FFML/WL% were different between the two groups (Pbetween < 0.05). The results showed a better FFM preservation and a greater FM loss over time in the OAGB group compared to the SG group (Pinteraction < 0.05). FFML during the first 3 months was greater in the SG compared to the OAGB group (P < 0.001). SG surgery, higher preoperative BMI, and female gender were associated with greater FFML/WL%.


In the SG compared to the OAGB group, FFML was greater, especially early after the surgery, emphasizing the need for therapeutic interventions such as regular exercise programs and dietary intake modifications.

Graphical abstract

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The authors would like to thank the hospital staff, study assistants, and coordinators that took part in this research. Also, special thanks for Mohammadreza Golsibi for his assistance and support of the electronic data collection system. This article was derived from the disease registry entitled “Registration of patient in Tehran Obesity Treatment Center” and approved under the ethical code of “IR.SBMU.ENDOCRINE.REC1397.059” (date: 2018-05-08) by the local ethic committee.


The study was supported by the deputy of research and technology of Shahid Beheshti University of Medical Sciences (

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Corresponding author

Correspondence to Farhad Hosseinpanah.

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Ethical Approval

This study was approved by the institutional review board (no. IR.SBMU. ENDOCRINE.REC 1397.0592018–05-08). Informed consent was obtained from all the participants included in the study. All procedures were performed in accordance with the ethical standards of the institutional and national research committees and the 1964 Helsinki declaration and its later amendments.

Informed Consent

Informed consent was obtained from the participant included in the study.

Conflict of Interest

The authors declare no competing interests.

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Cite this article

Barzin, M., Heidari Almasi, M., Mahdavi, M. et al. Body Composition Changes Following Sleeve Gastrectomy Vs. One-Anastomosis Gastric Bypass: Tehran Obesity Treatment Study (TOTS). OBES SURG 31, 5286–5294 (2021).

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  • Body composition
  • Sleeve gastrectomy
  • One-anastomosis gastric bypass
  • Fat mass
  • Fat-free mass