BEYOND Weight Loss Study

All participants will receive the Counterweight Plus dietary intervention. This consists of: * 12-20 weeks 800+ calories/day Total Diet Replacement Plan, followed by * 6-8 weeks Food Reintroduction, followed by * up to 104 weeks Weight Loss Maintenance, based on maintaining daily calorie restriction. All participants will undergo the following investigations at baseline and at regular intervals throughout the study period: * height (baseline only) * whole body MRI scans: total-body skeletal muscle volume and fat mass will be measured using whole-body multi-slice MRI (baseline and 12 weeks only) * functional assessment: completion of the Western Ontario and McMaster Universities Arthritis Index (WOMAC) (baseline and 12 weeks only) * gait and muscle strength assessment: biomechanical gait analysis will be carried out using an 8 camera VICON system during flat walking to determine maximum flexion and extension moments for both limbs and maximum adduction and abduction moments. Muscle strength will also be directly measured of both the upper (grip strength) and lower (quadriceps and hamstrings) limb using a dynamometer and myometer (baseline and 12 weeks only) * anthropometric measurement: body weight; waist, hip, thigh, arm and calf circumferences * indirect calorimetry: resting metabolic rate will be measured by a computerised open-circuit ventilated hood system * fasting blood sampling: for measurement of HbA1C, lipid profile, leptin, thyroid hormones * gut microbiota analysis from faecal samples * Binge Eating Disorder and Quality of Life (EQ-5D) questionnaires Participants will receive regular support/advice from a research dietician/ nutritionist during the two year study period.