The effect of tri-iodothyronine (T3) on protein turnover and metabolic rate

Obese patients who had an unusually slow weight loss on a restricted energy intake (2 MJ/d) were treated for approximately two weeks with small doses of T3 (20 micrograms three times daily). At the beginning and end of treatment whole body protein turnover was measured with a single dose of 15N-glycine and both ammonia and urea as end-products. T3 increased the rate of weight loss, with a significant increase in urinary nitrogen excretion. There were small increases in basal metabolic rate and protein turnover, which were not significant. It is concluded that the extra weight loss produced by T3 was at the expense of lean body mass and not of fat.