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

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.