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Decreased physical activity contributes to weight gain during treatment of hyperthyroidism
The
background of the study. Patients with hyperthyroidism often
lose weight. With treatment, they not only regain the lost weight but
also gain more weight. In this study, changes in energy expenditure and
the role of physical activity in determining energy expenditure were measured
in patients with hyperthyroidism before and after treatment.
How the study was done. The study included 8 patients with hyperthyroidism and 8 normal subjects. The patients were evaluated before treatment and then again when euthyroid approximately 12 months after treatment with an antithyroid drug or radioiodine. Each study consisted of measurements of 24-hour energy expenditure, energy expenditure during sleep, basal metabolic rate, foodstuff oxidation in a respiratory chamber, and fat mass and fat-free mass. Physical activity was monitored by motion detectors in the chamber.
The results of the study. The patients with hyperthyroidism gained weight after treatment, due to an increase in fat mass. Their 24-hour energy expenditure, 24-hour energy expenditure adjusted for fat mass, energy expenditure during sleep, basal metabolic rate, and 24-hour spontaneous physical activity all decreased after treatment.
As compared with the normal subjects, energy expenditure adjusted for fat-free mass and energy expenditure during sleep were higher, and energy balance was more negative, in the patients, but 24-hour physical activity was not different. After treatment, energy expenditure and spontaneous activity were lower than in the normal subjects, and the decreases correlated with the decrease in serum thyroid hormone concentrations.
The conclusions of the study. Energy expenditure, but not physical activity, is increased in patients with hyperthyroidism. With treatment, both decrease in proportion to the fall in serum thyroid hormone concentrations, suggesting that the excess weight gain sometimes associated with treatment of hyperthyroidism is caused by overly aggressive antithyroid therapy.
The original article. Jacobsen R, Lundsgaard C, Lorenzen
J, Toubro S, Perrild H, Krog-Mikkelsen I, Astrup A. Subnormal energy expenditure:
a putative causal factor in the weight gain induced by treatment of hyperthyroidism.
Diabetes Obes Metab 2006;8:220-7.
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