Does preoperative dietitian-led Very Low Calorie Diet (VLCD)-based intervention reduce unfavourable elective surgery outcomes for patients with obesity?

The intervention is a Very Low Calorie Diet (VLCD) which utilises meal replacement products (Optifast or Optislim) providing ~800kcal/day and will be individualised through dietitian-led treatment. The VLCD will include the oral consumption of 1-4 meal replacement products, with an additional 2 cups of non-starchy vegetables and at least 2 litres of non-caffeinated, calorie-free fluids. Dependent on lifestyle factors, age, and ability to adhere to the diet, participants will be recommended to consume variations of the described VLCD, utilising 1-4 meal replacement products, and specific portions of allowed foods. The diet will be prescribed by the dietitian at the participants' first dietitian appointment, which will be 4-12 weeks away from surgery, depending on surgery type and category (waiting times) for surgery. The participants will be asked to start the diet as soon as they can following the first dietitian appointment (where education regarding the diet will be given). Participants will attend from 2-6 dietitian appointments where they will be weighed and adherence to the diet will be monitored. The dietitian appointments will be administered via an outpatient (clinic) hospital setting, and the participants will be asked to follow the diet at home while undertaking their usual life. They will not be admitted to hospital for administration of the intervention. To monitor adherence, a dietary adherence tool will be used to measure self-reported prescription to the diet. This diet measures how many days within the last 14 days where the diet was adhered to according to specific measures of adherence (i.e. number of products, times 'non-allowed foods' were eaten) to create an overall % adherence measure.