Effects of a 'physiological' dose of triiodothyronine on obese subjects during a protein-sparing diet.

Twenty obese euthyroidian women followed an exclusively proteic diet for 18 days (74 g/day). Half received placebo, and half received 10 micrograms L-triiodothyronine. In the control group, as expected, mean weight loss was 7 percent of initial body weight; serum T3 and TSH decreased; rT3 increased; basal oxygen consumption diminished by 11 percent; nitrogen balance reached equilibrium at day 11. As compared to this group, the T3-treated group lost significantly more weight; serum T3 and TSH increased; rT3 decreased; oxygen consumption remained stable and nitrogen balance did not deteriorate. Thus, the physiological decrease in thyroid hormones provoked by a restricted diet is linked to energy expenditure but not to nitrogen balance equilibrium.