Intensive Weight Loss Intervention Versus Usual Care for Adults With Severe and Complex Obesity

In the LightWAY trial, an intensive weight loss (IWL) intervention will be compared with with usual care. The IWL lasts two years, and includes total dietary replacements, behavioural support, and weight loss medication in three phases: * Induction' phase (week 0-12 after randomisation): total dietary replacement (TDR) programme and behavioural support with weight loss medication (WLM) if rate of weight loss is insufficient. * Weight loss continuation' phase (week 13-32 after randomisation): progression of dietary programme including reduction in use of TDR products, reintroduction of healthy foods, with behavioural support, introduction of physical activity, WLM (as required). * Maintenance' phase (week 33-104 after randomisation): Continued healthy diet and physical activity with WLM (if required), with return to induction phase if weight regain occurs induction, weight loss continuation, maintenance. Usual care will differ between the two countries (Denmark and the United Kingdom). In Denmark, participants will receive a pamphlet on current obesity management guidelines from the Danish National Board of Health, and will be advised to contact their GP for potential referral to local municipality-based obesity management programmes. Furthermore, a notification will be sent to the participant's GP, informing that the participant has been enrolled in the trial and is randomised to usual care. The availability and structure of current obesity programmes varies between municipalities. In the United Kingdom, participants are eligible for referral into an NHS Tier 3 weight management service. These services are commissioned by integrated care boards, and can therefore differ slightly across the 42 regions within the UK. These are specialist weight management clinics that provide non-surgical, intensive medical management with a multidisciplinary approach to care. These clinics often consist of specialist doctors, nurses, dieticians and physiotherapists/exercise therapists, and include psychological support.