Thyroid function changes after bariatric surgery in untreated euthyroid patients: a comparative study of sleeve gastrectomy and Roux-en-Y gastric bypass

Objective: Obesity is associated with functional alterations in the hypothalamic–pituitary–thyroid (HPT) axis. Although bariatricsurgery induces substantial weight loss and metabolic improvement, postoperative thyroid hormone changes and potential differencesbetween surgical procedures remain unclear.Patients and Methods: This retrospective cohort study included 165 patients with obesity who underwent sleeve gastrectomy (SG,n=133) or Roux-en-Y gastric bypass (RYGB, n=32) between 2016 and 2020. Patients receiving thyroid-related treatment were excluded.Anthropometric, metabolic, and thyroid function parameters were assessed at baseline and 12 months postoperatively. Within-groupand between-procedure changes were analyzed using nonparametric tests. Associations between hormonal and metabolic changeswere evaluated using Spearman’s rank analysis.Results: At baseline, 99.4% were euthyroid. At 12 months, significant reductions occurred in body weight, body mass index (BMI), fastingglucose, glycated hemoglobin (HbA1c), insulin, thyroid-stimulating hormone (TSH), free thyroxine (fT4), and free triiodothyronine(fT3) (all p