Thyroid function studies in fasting obese subjects

Serial measurements of thyroid function were carried out in eleven obese euthyroid patients (8 females, 3 males) during a 21–27 day fast preceded and followed by several days on a 900 calorie diet. Weight loss during the fasting period averaged 0.98 lb./day. Thyroid function studies revealed (1) no significant change in PBI or total serum thyroxine; (2) an increase in the T3 resin uptake in all patients; (3) a decrease in the thyroxine-binding globulin (TBG) and thyroxine-binding prealbumin (TBPA) in 8 11 patients; (4) a rise in the serum free thyroxine to greater than normal levels in 8 11 patients; (5) no significant changes in the 24 hr. thyroid uptake of I 131. Alterations in hepatic function during the fast were reflected in an increased BSP retention in three patients studied and decreased total serum proteins in six patients. Alterations in hepatic function during starvation probably result in a diminished hepatic synthesis of TBPA and TBG. The decreased thyroxine-binding capacity of the serum proteins contribute to the elevated free thyroxine and T3 resin uptake. The significance of the elevated free thyroxine values is discussed.