In sleeve gastrectomy (SG) a large part (80%) of the ventricle is removed. The greater curvature will be dissected free starting 4-5 cm from the pylorus up to the angle of Hiss. The left crus is then visualized and inspected for hiatal hernia. Small sliding hernias and wide hiatus are left in situ. The ventricle will then be lifted and any adhesions in the lesser sac divided. A 35 Fr bougie is placed down to the pylorus guiding the creation of a tubular sleeve with linear staplers. The first two loads are always green or purple, while blue or tan loads are used for the rest of the ventricle. The last stapler is placed 5 mm laterally to the angle of Hiss. The staple line will then be inspected and secured with clips for additional haemostasis, no oversewing or buttressing material is routinely used.

The SASI bypass will performed with a similar entry of the abdominal cavity. A 6-port set up and a liver retractor is utilized. The small bowel is measured 300cm from the ileocecal valve, in sequences of 10cm, with the small bowel stretched and markers placed on the graspers, and connected to the antrum of the stomach with a 45mm stapler. The anastomosis is positioned slightly ventral on the antrum. The antrum is opened ventrally 5 cm proximal to the pylorus, just below the horizontal axis of canalis pylori. A 12 mm port positioned left to the midline is used for introduction of the stapler, which is directed distally from the patient's left to right side. 2.5 cm of the 45 mm stapler device is used for firing the anastomosis, which is completed with a 2-0 PDS running suture. The fascia defect is closed for the port where the specimen is extracted. The mesenteric defect is not closed.

Need-Threat Scale: 4 sub-scales: (1) Belonging, (2) Self-Esteem, (3) Meaningful existence, (4) Control; range: 3-27 per sub-scale; higher values indicate more belonging, higher self-esteem, higher meaningful existence, and more control)

Subjective ratings on a digitally presented visual analogue scale (VAS) scale: range 0-100 (unpleasant - pleasant) after a touch stimulation to the forearm (repeated 10 times)

Subjective ratings on a digitally presented VAS scale: range 0-100 (unpleasant - pleasant), after participants made 10 back-and-forth strokes on their forearm with their hand

Subjective ratings on a digitally presented VAS scale: range 0-100 (not intense - intense), after a touch stimulation to the forearm (repeated 10 times)

Subjective ratings on a digitally presented VAS scale: range 0-100 (not intense - intense), after participants made 10 back-and-forth strokes on their forearm with their hand

Participants are instructed to stroke their own forearm with a velocity they experience as pleasant. The duration of 10 back-and-forth strokes over a 10 cm distance on the forearm will be measured with a stop watch. Velocity in cm/sec will be calculated thereafter.

Cortisol (in pg/mg)

Endocannabinoids (in pg/mg)

Ghrelin (in pg/ml)

Questionnaires: Appearance Evaluation Scale (AES) and the Body Areas Satisfaction Scale (BASS) - the AES was designed to measure overall satisfaction/dissatisfaction with one's appearance and physical attractiveness. It has 7 items (range: 5-35) with high scores indicating body satisfaction and low scores indicating body dissatisfaction. The BASS was designed to measure the degree of dissatisfaction-satisfaction with specific body areas and attributes (range: 9-45). Higher scores indicate greater body satisfaction and lower scores indicate greater body dissatisfaction.

Questionnaire: Temporal Experience of Pleasure Scale (TEPS) - the TEPS was designed to measure individual trait dispositions in both anticipatory and consummatory experiences of pleasure. It consists of 18 items, of which 10 form the (1) anticipatory pleasure scale (range: 10-60), and (2) 8 items for the consummatory pleasure scale (range: 8-48). Higher values on (1) indicate enhanced reward responsiveness and imagery, while higher values on (2) indicate higher openness to different experiences and appreciation of positive stimuli.

Questionnaire: Body Awareness Questionnaire (BAQ) - the BAQ was designed to assess self-reported attentiveness to normal nonemotive body processes, such as sensitivity to body rhythms, ability to detect small changes in normal bodily functioning, and one's ability to anticipate bodily reactions. It consists of 18 items (range: 18-126). Higher values indicate a higher sensitivity and awareness of one's bodily states.

Questionnaires: The Social Connectedness Scale Revised (SCS-R) and the Social Assurance Scale (SAS). The SCS-R was designed to measure a psychological sense of belonging, or how individuals cognitively construe interpersonal closeness with others in their social world. It consists of 20 items (range: 20-120), with higher values indicating a higher sense of belonging. The SAS was designed to measure the importance of assurance from one's social group.It consists of 8 items (range: 8-48), with higher values indicating a higher need for social assurance.

Questionnaire: The Social Network Index (SNI) - the SNI was designed to measure three aspects of one's social networks: (1) network diversity, (2) number of people in the network, and (3) number of embedded networks. Each of the three sub-scales is assessed on 12 items. (1) refers to the number of high-contact roles (range: 0-12), with higher values indicating a higher number of social roles. (2) refers to the total number of people with whom the respondent has regular contact, which will be summed for the 12 items (range: 0-70). Higher numbers indicate more people in one's network (to not inflate the number, items 4-12 will be scored with 7 in case the reported number of people in this group is equivalent or larger to 7). The embedded network scale (3) reflects the number of different network domains in which a respondent is active (range: 0-8), with higher numbers indicating activity in more network domains.

Questionnaire:The Three Factor Eating Questionnaire -R 21 (TFEQ-R21) measures eating behaviour and has been validated for use in individuals with obesity and will be used in the study. It consists of 21 items comprising three domain scores; (1) uncontrolled eating; assessing the tendency to lose control over eating when feeling hungry or when exposed to external stimuli, (2) cognitive restraint; assessing the conscious restriction of food intake to control body weight or body shape, and (3) emotional eating; assessing overeating related to negative mood states. The domain scores were transformed to 0-100 scales to facilitate comparison; a higher score indicates more uncontrolled, restraint, or emotional eating.

Questionnaire: Hospital Anxiety and Depression Scale (HADS). The validated generic HADS measures symptoms of anxiety and depression using 14 items scored from 0-3 It is decomposed into two domains measuring depression (HADS-D) and anxiety (HADS-A), both consisting of seven items yielding a score from 0-21.

Generic questionnaire: Short Form-36 Health Survey (SF-36). Each item is scored on a 0 to 100 range so that the lowest and highest possible scores are 0 and 100, respectively. Scores for each of the 8 domains and summary scores for physical and mental health will be calculated.

Questionnaire: Weight-related Symptom Measure (WRSM). The validated obesity specific WRSM measures 20 symptoms commonly related to being overweight or obese, including foot problems, joint pain, sensitivity to cold, shortness of breath, etc. using two different sets of items. The first set assesses whether or not a patient is experiencing specific symptoms, and the second set rates the level of the distress of the symptoms with values from zero ("not at all") to six ("bothers a very great deal"). The first set creates an additive scale summing symptoms from 0-20, while the second forms a symptom distress scale ranging from 0-120.

Obesity specific questionnaire: The Impact of Weight on Quality of Life-Lite (IWQOL-lite). The IWQOL-Lite is a 31-item measure of weight-related quality of life. There are five domain scores (Physical Function, Self-Esteem, Sexual Life, Public Distress and Work) and a total score. Scores for all domains and total score range from 0-100, with lower scores indicating greater impairment.

10-item checklist assessing frequency and quality of daily social interactions (preprint in August 2025: https://osf.io/preprints/psyarxiv/6psar\_v2); 2 sub-scales: (1) Being with others, (2) Being alone; the diary will be filled in 14 days in a row at the end of the day. Scale (1) was designed to measure enjoyment of being with others and the duration of social contact (6 items, range: 4 to 62.4), higher values indicate more enjoyment and a higher frequency of social contact. Scale (2) was designed to measure enjoyment of being alone (3 items, range: -5 to 20), higher values here indicate more enjoyment of being alone. An additional item at the beginning of the checklists asks how many people the respondent has had social contact with during the day (5 categories).

The above-mentioned outcomes will be tested for differences between the two surgery types.

Waist and hip circumference (cm)

Body fat (in %)

Fat-free mass (in kg)

Systolic and diastolic blood pressure (mm/Hg)

Total-cholesterol, HDL-cholesterol, LDL-cholesterol and triglycerides (all in mmol/l)

HbA1c (mmol/mol); C-peptide (nmol/l)

CRP (mg/L)

ASAT (aspartate aminotransferase), ALAT (alanine-aminotransferase), LD (lactate dehydrogenase), Gamma-GT (gamma-glutamyl transferase), ALP (alkaline phosphatase) (all in U/L)

Hemoglobin (g/100 ml)

Ferritin ((µg/L)