A Study Comparing the Health Effects of Two Diets Following UK Dietary Guidance in People Living With Overweight or Obesity

There are two parts to this study:The investigators will study if the benefit from eating a healthy, balanced diet depends on the types of food processing in the diet. The investigators will do this by providing participants with two diets that follow the Eatwell Guide (referred to in this study as Diet A and Diet B to avoid unblinding), but containing foods with different types of food processing, for 8 weeks each. The investigators will collect data on blood pressure, body composition, physical activity and fitness, questions regarding quality of life, mental health and wellbeing, and blood samples at the start of each diet and at 4 and 8 weeks into each diet.The investigators will then study whether participants are able to switch from their usual unhealthy diet to a healthy, balanced diet, and the benefits of doing so. The investigators will do this by providing participants with 6 months of personal support. The investigators will also look at what helps participants to maintain a healthy diet, and what makes it difficult. The investigators will also support participants to be more physically active.

Inclusion Criteria:Staff at University College London Hospitals (UCLH)Adults aged between [18 and 65] years old.BMI ≥25 kg/m2 (living with overweight or obesity)Weight stable for the past 3 months (≤5 % variation in body weight over preceding 3 months)Have a habitual dietary intake high in unhealthy foodAble to read and write in English.Medically safe to participate in a dietary intervention programme.Willing and able to give written informed consent.Able to attend the relevant in person and online sessions.Able to comply with the study protocol (including dietary recommendations for each intervention and reporting adherence).Females of childbearing potential and males agree to use an effective method of contraception from the time consent is signed until the end of the intervention period and final follow-up assessment. Effective methods of contraception acceptable for this trial are outlined in Appendix 2.Females of childbearing potential must be on highly effective contraception and have a negative pregnancy test within 7 days of being randomised. NOTE: Participants are considered not of childbearing potential if they have undergone a hysterectomy, bilateral tubal ligation, or bilateral oophorectomy) or they are postmenopausal.Exclusion Criteria:Contraindication for dietary interventionParticipation in another clinical intervention trialConcomitant usage of medications that cause weight gain or weight lossCardiometabolic comorbidities (e.g. diabetes, on insulin)Coeliac diseaseInflammatory bowel diseaseA diagnosed eating disorderPlanning a weight management programme in the next 3 monthsAny diagnosed food allergy, or other allergies which limit the ability to adhere to the intervention dietDietary restrictions (e.g. vegan or vegetarian) which limit the ability to adhere to the interventionsBMI >40 kg/m2 or basal metabolic rate ≥2300/kcal/day (to ensure intervention diets are at least 300kcal/day greater than maintenance energy needs).Females who are pregnant, breast-feeding, or intends to become pregnant.A history of drug or alcohol abuseAny other factor making the participant unsuitable in the view of investigator.