Alterations in Thyroid Hormones in Obese Patients Are Associated With Body Composition Changes After Bariatric Surgery

CONTEXT: This article mainly explored the relationship between body composition and thyroid function in euthyroid obesity through correlation analysis, which showed the significant changes of thyroid function after bariatric surgery notably correlated with changes in body composition. OBJECTIVE: This study investigates how metabolic/bariatric surgery (MBS) affects thyroid hormone (TH) levels and TH resistance in obese euthyroid individuals, focusing on their correlation with changes in body composition. METHODS: We included 470 obese individuals and 118 controls for baseline assessment, and 125 obese patients receiving MBS for longitudinal study. Data on body composition and thyroid function were collected. Correlations between baseline and changes in thyroid function and body composition were assessed. RESULTS: In the obese group, thyrotropin (TSH), free triiodothyronine (fT3) levels, and thyroid feedback quantile-based index (TFQI) were elevated and significantly decreased post MBS, along with visceral fat area (VFA) and body fat percentages, whereas skeletal muscle mass (SMM) percentage increased. Preoperative partial correlation analysis adjusted for age and sex revealed that TSH positively correlated with VFA (r = 0.109; P = .019), body fat percentage (r = 0.114; P = .013), and negatively correlated with SMM percentage (r = -0.104; P = .024). Similar correlations were observed between central TH resistance indices and body composition, but no statistically significant correlations were found in the control group. Post MBS, decreased TSH positively correlated with decreased VFA (r = 0.251; P = .006) and increased SMM percentage (r = 0.233; P = .011). While reductions in VFA and body fat percentage were linked to improved central TH resistance, a decrease in peripheral TH conversion was noted. CONCLUSION: MBS significantly affects thyroid function and TH resistance, with notable correlations to changes in body composition.