Effects of total fasting in obese women. I. Response of the thyroid.

The values of serum T4, T3, T4/T3, RT3U, FT4I, PBI, ATR, TSH, 132I uptake and antibodies against thyreoglobulin were estimated in non-obese, healthy women and in obese women with a stabile body weight on total fasting of 14 days. Obesity with no dietary restriction compared with normal controls was accompanied by a tendency to higher serum levels of T4 and T3 and prolonged ATR. Other indicators of thyroid function remained unchanged. Total fasting led to a decrease of serum T3 and to an increase of FT4I and RT3U. The remaining tests were unchanged. These results are conform with a decreased transformation of T4 into T3 in the periphery. The participation of the hypothalamus and hypophysis to adaptation of the thyroid to fasting was discussed.