Background: Thyroid function within the normal range has been shown to influence body weight in a population. Even slightly elevated serum TSH levels are associated with an increase in the occurrence of obesity. It is unclear whether significant weight loss has the reverse effect on thyroid function, and studies to date have yielded inconsistent results.
Aims: Our aim was to describe changes in TSH and fT4 in relation to durable and significant weight loss in obese people with normal thyroid function before and after Roux-en-Y gastric bypass (RYGB) surgery.
Methods: We conducted a retrospective cohort study in 55 patients (13 men) who had undergone RYGB. Data recorded included TSH, fT4 and excess weight loss at baseline and median 4.5, 15 and 24 months after RYGB. Means were compared by t-test.
Results: Patients had a mean (S.E.M.) preoperative BMI of 48.1 (1.58) and achieved significant weight loss over time. Mean (S.E.M.) baseline serum TSH levels was 2.00 (0.14) mU/l with no significant change over time (2.02 mU/l at 24 months). Mean (S.E.M.) baseline fT4 concentrations were 13.02 (0.42) pmol/l, and increased significantly following bariatric surgery to 15.20 (0.57) pmol/l at 24 months (P<0.0001).
Conclusion: Weight loss after RYGB is accompanied by significant increase in fT4 but no change in TSH. Further work is required to address the mechanism of alteration in the pituitarythyroid axis after weight loss.