RESUMEN
OBJECTIVE: Obesity and weight loss influence thyroid hormone physiology. The effects of weight loss by calorie restriction vs Roux-en-Y gastric bypass (RYGB) in obese subjects have not been studied in parallel. We hypothesized that differences in transient systemic inflammation and catabolic state between the intervention types could lead to differential effects on thyroid hormone physiology. DESIGN AND METHODS: We recruited 12 lean and 27 obese females with normal fasting glucose (normal glucose tolerant (NGT)) and 27 obese females with type 2 diabetes mellitus (T2DM) for this study. Weight loss was achieved by restrictive treatment (gastric banding or high-protein-low-calorie diet) or by RYGB. Fasting serum leptin, TSH, triiodothyronine (T3), reverse T3 (rT3), and free thyroxine (fT4) concentrations were measured at baseline and 3 weeks and 3 months after the start of the interventions. RESULTS: Obesity was associated with higher TSH, T3, and rT3 levels and normal fT4 levels in all the subjects when compared with the controls. After 3 weeks, calorie restriction and RYGB induced a decline in TSH levels and a rise in rT3 and fT4 levels. The increase in rT3 levels correlated with serum interleukin 8 (IL8) and IL6 levels. After 3 months, fT4 and rT3 levels returned to baseline levels, whereas TSH and T3 levels were persistently decreased when compared with baseline levels. No differences in the effects on thyroid hormone parameters between the interventions or between NGT and T2DM subjects were observed at any time point. CONCLUSIONS: In summary, weight loss directly influences thyroid hormone regulation, independently of the weight loss strategy used. The effects may be explained by a combination of decreased leptin levels and transient changes in peripheral thyroid hormone metabolism.