Improving Compliance with Very Low Energy Diets (VLEDs) Prior to Bariatric Surgery—a Randomised Controlled Trial of Two Formulations

Lucy Davenport, Yazmin Johari, Alexandria Klejn, Cheryl Laurie, Andrew Smith, Geraldine J. Ooi, Paul R. Burton, Wendy A. Brown

Research output: Contribution to journalArticleResearchpeer-review

1 Citation (Scopus)


Introduction: Preoperative very low energy diets (VLEDs) improve access during bariatric surgery. Compliance with traditional VLED is variable, mainly due to gastrointestinal side effects. Formulite™ is a new formulation of VLED, with higher protein, soluble fibre and probiotics. Aims: To compare traditional VLED (Optifast™) with the new VLED (Formulite™) and assess compliance, weight loss, satisfaction, side effects and surgical access. Methods: This was a randomised double-blinded study involving patients scheduled for bariatric surgery. The primary outcome was compliance, assessed by urinary ketone concentration and proportion of patients in ketosis at 2 weeks. Secondary outcomes were weight loss, satisfaction and patient reported outcomes, gastrointestinal side effects and operative conditions. Results: There were 69 participants: 35 in the Formulite™ group and 34 in the Optifast™ group. Ketosis at 2 weeks was achieved in both groups (88.5% vs 83.3%, Formulite™ vs. Optifast™, p = 0.602). Urinary ketones were higher with Formulite™ (1.5 vs 15 mmol/L, p = 0.030). Total body weight loss percentage, hunger and operative conditions were similar in both groups. Formulite™ produced less flatulence (score 3 vs 2, p = 0.010) and emotional eating (score 2 vs 1, p = 0.037); however, Optifast™ ranked higher in terms of taste (score 4 vs 3, p = 0.001) and overall satisfaction (score 5 vs 7, p = 0.011). Conclusions: Compliance over 2 weeks was high in both VLEDs with most subjects achieving ketosis. Overall satisfaction was moderately high, although variable. Whilst Formulite™ is a viable alternative to Optifast™, better formulations of VLED that addresses key adverse effects, whilst achieving ketosis, would be of significant value.

Original languageEnglish
Pages (from-to)2750-2757
Number of pages8
JournalObesity Surgery
Issue number9
Publication statusPublished - 15 Sep 2019


  • Bariatric surgery
  • Compliance
  • Very low energy diet

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