Evaluation of serum leptin levels and thyroid function in morbidly obese patients treated with bariatric surgery

Biliopancreatic diversion (BPD), a gastrectomy with a long ROUX en Y reconstruction, reduces intestinal absorption by delaying the mixing of food and biliopancreatic juices, and induces persistent weight loss in obese patients unresponsive to medical treatments. The levels of leptin (a plasma protein synthesised in human adipose tissue) are increased in obese subjects and significantly decrease after a major weight loss. A possible role of thyroid hormones in regulating adipose tissue metabolism in humans has been proposed, but it is not universally accepted and the relationship between thyroid function and leptin levels has not yet been clearly defined. We studied serum leptin, TSH, fT4 and fT3 levels in 38 obese patients (26 women and 12 men), before and 12 months after BPD. There was a significant post-surgical decrease in BMI and circulating leptin levels in all of the treated subjects, but thyroid function did not seem to be affected (TSH and fT4 levels were unchanged). However, fT3 levels significantly decreased after surgery. Our data suggest that BPD-induced malabsorption has no direct effect on thyroid function, but possibly reduces the peripheral conversion of thyroxine to T3. Further studies seem to be necessary to clarify the clinical relevance of these observations.