Currently, a ketosis-inducing programme, usually a liquid meal replacement, is the standard of care for pre-operative dietary management. However, compliance with liduiqd meal replacement is challenging primarily due to individual taste preferences, limited variety, having to take a liquid diet, lifestyle factors, and other obstacles. Therefore, there is a need for RTE meals to enhance patient satisfaction and compliance, ultimately resulting in improved pre-operative weight loss outcomes. Hence, this RCT study aims to determine whether Very Low Calorie Diet Ready-to-eat (VLCD RTE) meals would lead to greater compliance as measured by blood ketones and meal logging via Nutritionist Buddy app (nBuddy App) compared to standard care liquid meal replacement (Optifast) prior to bariatric surgery.

The obesity rate in Singapore is rising, mirroring a similar worrying global trend. Bariatric surgery has been the only long-term method proven to overcome severe obesity and it has become an increasingly common and effective treatment option. Preoperative weight loss is required to reduce cardiovascular risk, liver volume and decrease intra-abdominal fat. This leads to enhanced surgical visibility and surgical access resulting in reduced intra- and postoperative complications.

Currently, a ketosis-inducing programme, usually a liquid meal replacement, is the standard of care for pre-operative dietary management. However, compliance with liquid meal replacement is challenging primarily due to individual taste preferences, limited variety, having to take a liquid diet, lifestyle factors, and other obstacles. It was found for taste and gastrointestinal side effects to be the main issues.

Therefore, RTE meals are carefully formulated to provide the calculated calorie, controlled net carbohydrate content, and are low in saturated and trans fat. By incorporating these meals as a VLCD diet regime, it would allow patients to still enjoy the chewing sensation and local favourites and flavours, while enjoying mealtime with their friends and families.

In this randomised controlled trial, patients listed for bariatric surgery from the NUH Weight Management Clinic in Singapore will undergo randomization into either the Standard Care or Intervention group during the baseline visit.

• Standard Care Group (n=70): Participants will be provided with liquid meal replacements for breakfast, lunch, and dinner for 4 weeks. Additionally, patients are to prepare 1 serving of non-starchy vegetables are to be included for lunch and dinner.
• Intervention Group (n=70): Participants will be provided with the VLCD RTE meals for lunch and dinner for 4 weeks and advised on a healthy keto breakfast.

All eligible participants (n=140) will be advised to keep within the 800 calorie limit and 50g net carbohydrate limit per day. They will receive guidance from a dietitian on lifestyle changes and pre-bariatric surgery VLCD diets. Participants in both groups will also be advised to download the nutritionist Buddy Keto app for monitoring of compliance, food intake, steps count, weight progress and in app virtual reminders (automated and by dietitians via the chat function).

Inclusion Criteria:

• Adults aged 21 to 65 years old
• Scheduled for bariatric surgery at least 1 month prior
• BMI ≥ 27.5 kg/m2 (with type 2 diabetes mellitus or metabolic syndrome)
• Owns a smart phone with data plan
• English speaking

Exclusion Criteria:

• Cognitive impairment.
• Hypothyroidism
• Chronic kidney disease
• Hypothyroidism
• Depression with ongoing psychology follow up
• Type 1 diabetes
• Liver Cirrhosis
• Pregnancy
• Heart Failure
• Active cancer or in remission for less than 5 years
• Vegetarian
• Observing the fast during the month of Ramadan
• Undergoing treatment with anti obesity medications (eg: Phentermine/Orlistat/Contrave/GLP-1 analogues etc)

Individual participant data will remain confidential and only accessible via lock and keys by the researchers.

It is not feasible to apply blinding to the study design due to the nature of the intervention.