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

To take part in this study, you need to be specifically invited. You must be an adult between 18 and 60 years old. You also need to have severe obesity, specifically a high body mass index (BMI over 35), or a slightly lower BMI (over 32.5) if you have South Asian, Chinese, other Asian, Middle Eastern, Black African, or African-Caribbean family backgrounds and have other health conditions linked to weight, such as heart disease, type 2 diabetes, high blood pressure, certain liver conditions, or sleep apnoea.

There are also reasons why you might not be able to join. For example, if you plan to get pregnant, are pregnant, or breastfeeding within the next two years. You also can't have used weight-loss medicines, including certain types of diabetes medication (GLP-1s), in the last three months. If you've had certain types of weight-loss surgery in the past (like gastric bypass), or are currently being treated for most cancers, you wouldn't be able to participate.

Other reasons for not being able to join include having a severe eating disorder recently, or if other health conditions would make it difficult for you to follow the study's plan or if weight loss wouldn't significantly improve your health or life expectancy. Also, if you have certain medical conditions that make special diets or specific weight-loss medications unsuitable, or if another member of your household is already in the study, you wouldn't be eligible.

If you are invited and decide to take part in this study, it will last for two years. You'll either be assigned to the intensive weight loss programme or to receive usual care.

If you're in the intensive weight loss group, you'll start with a 'dietary replacement' phase for about 12 weeks, meaning you'll mainly have special meal replacements. During this time, you'll also get support to help change your eating habits, and you might receive weight-loss medication if needed. After this, you'll gradually reintroduce healthy foods and begin physical activity, with continued support and medication if required. The final phase, lasting until the end of the two years, focuses on maintaining a healthy diet and active lifestyle, with ongoing support and medication as needed. If you regain weight, you might revisit earlier phases.

Both groups will have regular check-ups to monitor your health and progress throughout the two years. The exact number of visits will be explained by the study team, but they are important for tracking how well the different approaches work and to keep you safe.