L-thyroxine in the treatment of obesity without increase in loss of lean body mass

The present study compares the loss of body weight and lean body mass observed in obese patients while receiving a restricted (600 cal) diet with that obtained in the same individuals while receiving a more satisfying (1200 cal) diet plus a large dose of L-thyroxine (T₄). Four massively obese male patients were studied. Two patients had one period of 600-cal diet plus T₄ 0.3 mg/day interposed between two periods of 1200-cal diet plus T₄ 0.9 mg/day. The other two patients had one period of 1200-cal diet plus T₄ 0.9 mg/day interposed between two periods of 600-cal diet plus T₄ 0.3 mg/day. Both diets were constant and relatively high in protein. Their activity program did not change when they changed diet and T₄ dose. None of the patients had any serious side effects. There was no significant difference in the amount of weight lost on the two protocols. Each patient lost more body water at the beginning of the study than at the end regardless of the protocol. The average negative nitrogen balance during the two treatments was approximately equal. It appears from the present study that under appropriate circumstances, moderately large doses of T₄ do not necessarily cause erosion of lean body mass. The role of T₄ in the treatment of special cases of obesity is worthy of further trial.