Primary weight loss failure after Roux-en-Y gastric bypass is characterized by impaired gut-hormone mediated regulation of food intake.

"Competing interests CM has received support from Novo Nordisk A/S for organizing/attending meetings. JEBJ and SST have received research grants and lecture fees from Novo Nordisk A/S. CD has served as advisor for Novo Nordisk A/S and AstraZeneca and received lecture fees from Novo Nordisk A/S. NBJ has served on advisory panels and in educational programs from Novo Nordisk A/S, has received research support from Boehringer Ingelheim Denmark. In addition, NBJ reports having taken a position with Novo Nordisk A/S as of March 2023. The remaining authors have no competing interests related to this study."

"Funding Open access funding provided by Royal Library, Copenhagen University Library."

"Eligible patients were identified using a database of > 600 patients operated with RYGB at Copenhagen University Hospital Hvidovre, Denmark in 2012–2015. Patients with primary WL failure (LowEBMIL, n = 20) were defined by postoperative EBMIL < 50% at all visits including 1 and 2 years postoperatively after uncomplicated RYGB. Each patient in the primary WL failure group was matched individually with one patient with successful WL (postoperative EBMIL > 60%, HighEBMIL, n = 20) with respect to age, preoperative BMI and time from RYGB. Only women without a history of diabetes (Hba1c < 48 mmol/mol without glucose-lowering medication) were included. Exclusion criteria were unstable weight (self-reported > ±3 kg in 3 months), inadequately treated hypothyroidism, use of antithyroid medication or medication affecting appetite, hemoglobin < 6.5 mmol/L, pregnancy/breastfeeding or unwillingness/allergies toward the test meals. The study was approved by the Regional Ethical Committee of the Capital Region (H-4–2014–007), by the Danish Data Protection Agency and was performed in accordance with the Helsinki declaration and registered at ClinicalTrials.gov (NCT02344632). Written informed consent was obtained from all participants before inclusion."