This study was in healthy young men (e.g., bodybuilders). Essentially, for every 2 pounds of fat loss, there is 1 pound of muscle loss. And the length of the study, 9 weeks, is slightly less than a typical AAS cycle leading to more muscle loss.
T3 treatment began following the 3-week run-in period and continued for 63 days (9 weeks). All subjects initially received 75μ g/day T3 (liothyronine sodium, Cytomel, Smith-Kline-Beecham, Philadelphia, PA) in five doses every 4 h during waking hours beginning at 0600 h.
This dose was chosen based on a previously described paradigm suggesting that this dose produced serum levels of approximately 4.6–5.4 nmol/L. The dose was reduced if a subject became symptomatic or if serum T3 levels exceeded 2 SD above the mean for the T3 assay in our laboratory (∼4.6 nmol/L).
All subjects but two received dose reduction to either 62.5 or 50 μg/day T3, in most cases due to higher than desirable levels of serum T3. The timing of dose reduction differed among subjects, with most subjects being reduced to 62.5 μg/day after approximately 2 weeks of treatment.
Lovejoy JC, Smith SR, Bray GA, et al. A Paradigm of Experimentally Induced Mild Hyperthyroidism: Effects on Nitrogen Balance, Body Composition, and Energy Expenditure in Healthy Young Men. J Clin Endocrinol Metab 1997;82(3):765-70. http://jcem.endojournals.org/content/82/3/765.long
Although T3 exerts major regulatory actions in both animals and humans, most clinical studies of T3 administration have been relatively short term. The present study examined the effects of more than 2 months (63 days) of low dose T3 treatment on nitrogen balance, body composition, 24-h energy expenditure (EE), and protein turnover in seven healthy men studied at an in-patient metabolic unit. Subjects were also randomly assigned to either high or low fat diets to determine the effects of diet composition.
T3 treatment produced significant losses in both lean mass (1.5 {+/-} 0.3 kg) and fat mass (2.7 {+/-} 0.4 kg) by 6 weeks, with similar reductions in both at 9 weeks. The high fat diet somewhat attenuated the loss of body fat. Nitrogen balance was significantly negative for the first 3 weeks of T3 treatment, but tended to return to baseline thereafter. There were no significant effects of treatment on protein turnover at 9 weeks, although there was a slight increase in leucine oxidation (P = 0.07). Despite the apparent adaptation in nitrogen balance, total 24-h EE and sleeping EE were significantly increased at 9 weeks.
We conclude that although healthy men are able to adapt to mild hyperthyroidism in terms of nitrogen balance, they exhibit significant and persistent changes in fat and fat-free mass as well as energy balance.
