Low serum free T3 concentrations in postobese patients previously treated with very-low-calorie diet

Thirteen postobese patients with stable body weights were studied and compared with obese patients and normal subjects. Six had previously been treated with a very-low-calorie diet (VLCD) whereas seven had been treated with gastroplasty (GP). The median observation time of post-obesity was 20 months for GP patients, but significantly (P less than 0.001) shorter by 2 months in VLCD patients. The median serum concentration of free triiodothyronine (T3) was significantly (P less than 0.005) reduced in the postobese VLCD patients (3.4 pmol/l) but normal in postobese GP patients (4.2 pmol/l) and obese patients (4.5 pmol/l). The serum level of total T3 was correspondingly lowered in the postobese VLCD patients. Also the postobese GP patients had a small, but significant (P less than 0.01) reduction in the median serum concentration of total T3 suggesting a slight decrease in the binding capacity. The serum levels of thyroxine-binding globulin and thyroxine-binding prealbumin were normal in both postobese and obese patients. Furthermore, the serum levels of thyroxine were normal showing that the postobese patients were euthyroid. The study shows that serum concentrations of T3 are not associated with body weights and low serum concentration may be seen in postobese patients after VLCD.