Statisticians and investigators drawing conclusions will be fully blinded. We will conduct the statistical analyses with the intervention groups coded as e.g., 'A' and 'B'. We will write two abstracts while the blinding is intact; one assuming the experimental intervention group is 'A' and the control intervention group is 'B', and one assuming the opposite. After these two abstracts have both obtained consensus, the code will be broken by the data manager. whoMasked: INVESTIGATOR whoMasked: OUTCOMES_ASSESSOR count: 500 type: ESTIMATED name: Intensive weight loss intervention name: Bariatric surgery measure: MetS-Z measure: Weight measure: Gait speed measure: Short-Form-36, mental component score measure: SAE measure: Proportion of participants with at least one adverse events (AE) of special interest. Each of the AE will also be assessed individually exploratorily. measure: Cardiometabolic health - metabolic syndrome measure: Cardiometabolic health - blood pressure measure: Cardiometabolic health - pulse measure: Cardiometabolic health - glucose measure: Cardiometabolic health - Hb1Ac measure: Cardiometabolic health - insulin measure: Cardiometabolic health - HOMA2-IR measure: Cardiometabolic health - lipids measure: Cardiometabolic health - eGFR measure: Cardiometabolic health - hsCRP measure: Cardiometabolic health - Fib-4 measure: Cardiometabolic health - proteinuria measure: Cardiometabolic health - TSH measure: Weight and body composition - weight loss measure: Weight and body composition - waist circumference measure: Weight and body composition - body fat and lean body mass measure: Physical functioning - sedentary and active measure: Physical functioning - sit to stand test measure: Medication use measure: Micronutrient status, assessed as proportion of participants with deficiency measure: Bone mineral density (BMD) assessed by DXA measure: Sleep - ESS measure: Sleep - sleep and wake time measure: Sleep - sleep movement measure: Health-related quality of life and mental health - EQ-5D-5L, index score measure: Health-related quality of life and mental health - EQ-5D-5L, VAS measure: Health-related quality of life and mental health - SF-36 measure: Health-related quality of life and mental health - EDE-Q measure: Health-related quality of life and mental health - WBIS-M measure: Health-related quality of life and mental health - MDI measure: Labour market attachment - WPAI measure: Labour market attachment - days of sick leave measure: Continuous glucose monitoring - hypoglycaemic range measure: Continuous glucose monitoring - hypoglycaemic events measure: Continuous glucose monitoring - glucose variability measure: Continuous glucose monitoring - hypoglycaemic symptoms measure: Pending additional funding: Genetic profiles' (using comprehensive genetic mapping) association with the metabolic and/or weight loss response to IWL vs bariatric surgery measure: Health economy: Within-trial cost-effectiveness analysis - quality of life measure: Health economy: Within-trial cost-effectiveness analysis - costs measure: Health economy: Within-trial cost-effectiveness analysis - QALY measure: Health economy: Model-based cost-effectiveness analysis - QALY measure: Health economy: Model-based cost-effectiveness analysis - healthcare costs measure: Health economy: Model-based cost-effectiveness analysis - cost effectiveness ratios measure: Long-term effects - mortality and major cardiovascular disease (CVD) measure: Long-term effects - prescription patterns measure: Long-term effect - incident cancer measure: Long-term effect - surgical procedures measure: Long-term effect - fracture risk measure: Long-term effect - health economic and labour market attachment, employment status measure: Long-term effect - health economic and labour market attachment, salary measure: Long-term effect - health economic and labour market attachment, absence measure: Long-term effect - health economic and labour market attachment, sick leave measure: Long-term effect - health economic and labour market attachment, long-term sick leave sex: ALL minimumAge: 18 Years maximumAge: 60 Years stdAges: ADULT facility: Steno Diabetes Center Aarhus, Aarhus Universitets Hospital status: NOT_YET_RECRUITING city: Aarhus zip: 8200 country: Denmark name: Jens Bruun role: CONTACT lat: 56.15674 lon: 10.21076 facility: The Department of Medicine and Department of Surgery, University Hospital of South West Jutland status: NOT_YET_RECRUITING city: Esbjerg zip: 6700 country: Denmark name: Claus Borg Juhl role: CONTACT lat: 55.47028 lon: 8.45187 facility: The Department of Medicine and the Gastro Unit, Copenhagen University Hospital - Amager and Hvidovre status: RECRUITING city: Hvidovre zip: 2650 country: Denmark name: Kirstine N Bojsen-Møller role: CONTACT lat: 55.65719 lon: 12.47364 facility: The Department of Medicine and the Department of Surgery, Zealand University Hospital Køge status: NOT_YET_RECRUITING city: Køge zip: 4600 country: Denmark name: Merethe Hansen role: CONTACT lat: 55.45802 lon: 12.18214 facility: Department of Surgery, Viborg Regional Hospital status: NOT_YET_RECRUITING city: Viborg zip: 8800 country: Denmark name: Peter Rask role: CONTACT lat: 56.45319 lon: 9.40201 facility: Southmead Hospital, North Bristol NHS Trust status: NOT_YET_RECRUITING city: Bristol zip: BS10 5NB country: United Kingdom name: Dimitri Pournaras role: CONTACT lat: 51.45523 lon: -2.59665 facility: Southampton General Hospital, University Hospital Southampton NHS Foundation Trust status: NOT_YET_RECRUITING city: Southampton zip: SO16 6YD country: United Kingdom name: James Byrne role: CONTACT lat: 50.90395 lon: -1.40428 facility: Musgrove Park Hospital, Somerset Foundation NHS Trust status: NOT_YET_RECRUITING city: Taunton zip: TA1 5DA country: United Kingdom name: Richard Welbourn role: CONTACT lat: 51.01494 lon: -3.10293 hasResults: False