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Comparison of Preoperative Diets Before Bariatric Surgery: a Randomized, Single-Blinded, Non-inferiority Trial

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In order to increase weight loss and minimize complications, a preoperative diet before bariatric has been advocated. However, some diets are poorly tolerated by patients and this can lead to low compliance and too little weight loss. In this study, we aim to compare two preoperative diets in order to find the most suitable for this patient population.


Comparison of preoperative diets before bariatric surgery with a randomized non-inferiority trial in order to compare the standard very low calorie diet (VLCD) by protein shakes (Prodimed) with a standard diet using ordinary products. The primary outcome parameter was preoperative weight loss. Secondary outcome parameters were operation time, difficulty of surgery, short-term complications, short-term weight loss and compliance, tolerance, and acceptance of the diets.


Two hundred twelve patients suitable for gastric bypass surgery were included and randomized. The Prodimed group contained 105 patients, the standard diet group 107 patients. Preoperative weight loss and 4 weeks after the procedure were not significantly different between the two diet groups. Operation time, difficulty of surgery, short-term complications, and short-term weight loss were also comparable without significant differences between the diet groups. However, most of the parameters measuring patients’ compliance, tolerance, and acceptance of the diets were significantly better in the standard diet group as compared to the patients in the Prodimed group.


Protein shakes and standard diets are capable of achieving good and comparable results on preoperative weight loss before bariatric surgery. However, patients’ compliance, tolerance, and acceptance were all significantly better after a standard diet. We recommend giving patients a choice in preoperative diets in order to achieve the best possible weight loss and results.

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Correspondence to Ruben Schouten.

Ethics declarations

All procedures performed in studies involving human participants were in accordance with the ethical standards of the institutional and/or national research committee and with the 1964 Helsinki Declaration and its later amendments or comparable ethical standards.

Conflict of Interest

The authors declare that they have no competing interests.

Informed Consent

Informed consent was obtained from all individual participants included in the study.

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None declared.

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Schouten, R., van der Kaaden, I., van ’t Hof, G. et al. Comparison of Preoperative Diets Before Bariatric Surgery: a Randomized, Single-Blinded, Non-inferiority Trial. OBES SURG 26, 1743–1749 (2016).

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