National guidelines recommend 15-20% weight loss for severe and complicated obesity. Weight loss maintenance can be achieved in around 33% of patients at 12 months.

The BEYOND study will administer Counterweight Plus; a nutritionally replete Total Diet Replacement Plan (TDR) of 800+ Calories followed by structured Food Reintroduction, and Weight Loss Maintenance programmes.

The study will incorporate three work packages with the aim of:

1. examining changes in body composition with substantial (target >15kg) non-surgical weight loss (work package 1, WP1)
2. characterizing the metabolic adaptations during weight loss and maintenance (work package 2, WP2)
3. examining Rescue Packages as a method of weight re-gain prevention (work package 3, WP3).

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.

Inclusion Criteria:

• confirmation from general practitioner (GP) of suitability for intervention
• written informed consent
• female
• BMI ≥30 kg/m2 and < 45kg/m2, weight<200 kg and <60 cm bore size

Exclusion Criteria:

• known illness such as heart disease, cancer, or any disability that would affect weight loss (diabetes not an exclusion) or prevent completion of the intervention
• implanted electronic devices that are MRI incompatible or MRI unsafe, ferromagnetic foreign bodies
• substance abuse
• myocardial infarction within previous 6 months
• learning difficulties and subjects having difficulty in understanding verbal or written English
• pregnant/ considering pregnancy
• patients who have required hospitalisation for depression or are on antipsychotic drugs
• people currently participating in another clinical research trial
• recent weight loss >5kg within the last 6 months
• current treatment with anti-obesity drugs
• diagnosed eating disorder