Effects of diet, exercise and anorexigenic drugs on serum thyroid hormones

The serum levels of T4, T3 and rT3 were estimated in moderately obese women treated with diet (900-1000 kcal) and 4 h of exercise, supplemented with placebo or anorexigenic drugs (phenmetrazine, phentermine and mazindol). After 12 days of treatment, no change in serum T4 occurred in the placebo group (-4%), while in the groups with anorexigenic drugs a significant rise of T4 was observed (phenmetrazine +33%, phentermine +14% and mazindol +20%). Serum T3 decreased significantly in the placebo and the anorexigenic groups to a similar extent (from -21% to -27%) with the exception of mazindol. We did not notice any decrease of T3 in this group (-3%). A rising trend of serum rT3 was observed in all 4 groups, with a statistical significance for mazindol only. It is suggested that 1) a combined energy deficit produced by diet and exercise leads to a pattern of serum thyroid hormones similar to that observed in resting patients on a total fast; 2) the rise of serum T4 after the administration of anorexigenic drugs is due to their sympathomimetic effects; 3) the largest weight decrease observed in the mazindol group (6.7 kg) may be due to the unchanged serum T3 level, while in the other groups a decrease of serum T3 was observed. The lowest weight loss was observed in the placebo group (4.9 kg) with a pronounced decrease of T3 (-24%).