Obesity Surgery

, Volume 28, Issue 8, pp 2473–2480 | Cite as

Linear Mixed Effects Analysis Reveals the Significant Impact of Preoperative Diet Success on Postoperative Weight Loss in Gastric Bypass Surgery

  • Rebecca Kraus
  • Daniel J. Stekhoven
  • Ulrich Leupold
  • Walter R. Marti
Original Contributions



Several studies investigated the impact of preoperative weight loss on bariatric surgery outcome. However, they mostly focus on small groups of patients or lack updated statistical support.


Two hundred and thirty-nine consecutive patients undergoing laparoscopic, proximal Roux-en-Y gastric bypass at our institution between September 2009 and November 2015 were studied. Patients were operated by the same surgeon, applying a standardized technique and followed a 500-kcal/day preoperative diet, starting 14 days before surgery. Body weight was measured before diet, at surgery, and at least three times postoperatively. A linear mixed effects (LME) model and Benedict and Harris formula were used to assess association of pre- and postoperative weight loss up to 2 years postoperatively.


Patients’ (184 females) initial weight was 121.7 kg (females 117.2 kg; males 136.6 kg). They lost on average 5.3 kg (females 4.7 kg; males 7.0 kg) pre- and 36.8 kg (females 36.7 kg; males 37.0 kg) postoperatively, within 2 years. Average excess weight loss (EWL) was 67.2% (females 66.6%; males 67.4%). In 205 patients (154 females), EWL exceeded 50%. Longitudinal data analysis according to LME showed a significant impact of pre- on postoperative weight loss (p < 0.001, likelihood-ratio test, LRT). These effects were undetectable if patients were evaluated by non-parametric analysis based on application of the Benedict and Harris formula.


Preoperative dietary success is associated with postoperative weight loss. Effects predicted by the LME model are most pronounced in the first 4–6 months after surgery and are fading away within 24 months postoperatively. External factors not considered in this study might dominate in later phases.


Gastric bypass surgery Preoperative weight loss Linear mixed effects model 


Compliance with Ethical Standards

The study was approved by the Internal Review Board of the Kantonsspital Aarau (no. …., 200…).

Conflict of Interest

The authors declare that they have no conflict of interest.

Ethical Approval Statement

For this type of study, formal consent is not required.

Informed Consent Statement

Does not apply.

Supplementary material

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ESM 1 (JPEG 219 kb)
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ESM 2 (JPEG 437 kb)


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Copyright information

© Springer Science+Business Media, LLC, part of Springer Nature 2018

Authors and Affiliations

  1. 1.Department of SurgeryKantonsspital AarauAarauSwitzerland
  2. 2.Quantik AGBerikonSwitzerland

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